vertical and horizontal seismic profiling investigations at olkiluoto

Vertical and horizontalseismic profiling investigations

at Olkiluoto, 2001

P O S I V A O Y

F I N - 2 7 1 6 0 O L K I L U O T O , F I N L A N D

P h o n e ( 0 2 ) 8 3 7 2 3 1 ( n a t . ) , ( + 3 5 8 - 2 - ) 8 3 7 2 3 1 ( i n t . )

F a x ( 0 2 ) 8 3 7 2 3 7 0 9 ( n a t . ) , ( + 3 5 8 - 2 - ) 8 3 7 2 3 7 0 9 ( i n t . )

March 2003

POSIVA 2003 -01

Ca l i n CosmaNico le ta Enescu

Er i ck AdamLuc ian Ba lu

POSIVA 2003 -01

March 2003

Vertical and horizontalseismic profiling investigations

at Olkiluoto, 2001

C a l i n C o s m a

N ico le ta Enescu

E r i c k A d a m

L u c i a n B a l u

V ib romet r i c Oy

P O S I V A O Y

F I N - 2 7 1 6 0 O L K I L U O T O , F I N L A N D

P h o n e ( 0 2 ) 8 3 7 2 3 1 ( n a t . ) , ( + 3 5 8 - 2 - ) 8 3 7 2 3 1 ( i n t . )

F a x ( 0 2 ) 8 3 7 2 3 7 0 9 ( n a t . ) , ( + 3 5 8 - 2 - ) 8 3 7 2 3 7 0 9 ( i n t . )

ISBN 951 -652 -115 -0ISSN 1239 -3096

T h e c o n c l u s i o n s a n d v i e w p o i n t s p r e s e n t e d i n t h e r e p o r t a r e

t h o s e o f a u t h o r ( s ) a n d d o n o t n e c e s s a r i l y c o i n c i d e

w i t h t h o s e o f P o s i v a .

EXTENDED ABSTRACT

continued

Tekijä(t) � Author(s) Calin Cosma, Nicoleta /nescu, /ric2 Adam, Lucian Balu Vibrometric Oy

Toimeksiantaja(t) � Commissioned by Posiva Oy

Nimeke � Title

V/RTICAL AND HORIBONTAL S/ISMIC PROFILINF INV/STIFATIONS AT OLKILHOTO, 2001

Tiivistelmä � Abstract

Vertical Seismic Profiling NVSPO and Horizontal Seismic Profiling NHSPO surveys were conducted during 2001 at Ol2iluoto site in /uraRo2i, Finland. The VSP investigations were carried out in four boreholes with ten shot points for each borehole. Two HSP lines were measured with receivers laid on the bottom of an artificial pond and ten source points located around the pond. Different receiver types were used for the VSP and HSPV a 3-component geophone chain for VSP and a hydrophone chain for HSP. All surveys have been carried out with a VIBSIST-1000 source - a time-distributed swept-impact source - instead of eYplosives. Zith this source, the seismic signals are produced as rapid series of impacts, the impact intervals being monotonically increased to achieve a non-repeatable sequence. The VIBSIST-1000 uses a tractor-mounted hydraulic roc2-brea2er, powered through a computer controlled servo-hydraulic flow regulator. Hsing standard construction equipment ensures that the VIBSIST sources are safe, non-destructive and environmentally friendly. This also ma2es the method reliable and cost effective. The new VIBSIST source produces signals with levels of energy comparable to eYplosives. The VIBSIST appears to be more stable, but its most significant advantages are the low cost of preparation of the shot points and the speed of the acquisition. The wide diversity of reflection angles, the local variations of reflectivity and, generally, the relatively wea2 seismic response of faults and fractured zones in crystalline roc2 demand intensive processing. The first stage of the processing sequence focuses on eliminating such wave-fields as the direct P, direct S, tube-waves and ground-roll, so that the wea2er later events, e.g. reflections, become visible. The second stage of processing consists mainly of Image Point NIPO filtering techniques, aimed at enhancing the reflected wave fields and at separating events generated by reflectors with different orientations. Imaging techniques recently developed, such as the simultaneous determination of the orientation of the structural features from VSP surveys in several boreholes and Image Point wave field migration, were used eYtensively for the first time within this proRect. The \importance] of a reflector can be reliably quantified by its consistency amongst several profiles, which can in turn be interpreted as an indication of spatial eYtent and continuity. The interpretation was made using a combination of interactive modelling and IP Migration. The modelling was used to estimate the positions and orientations of the maRor reflectors, found consistently in the maRority of the profiles. The IP Migration was used as a trial of a new methodology to allow the interpretation of less visible reflectors belonging to the same orientation classes as the maRor ones.

Posiva-raportti � Posiva Report Posiva Oy FIN-27160 OLKILUOTO, FINLAND Puh. 02-8372 (31) � Int. Tel. +358 2 8372 (31)

Raportin tunnus � Report code

POSIVA 2003-01 Julkaisuaika � Date

March 2003

EXTENDED ABSTRACT

The VSP method has been found particularly suitable for surveys in crystalline roc2s, where sources spread on the surface at diverse azimuths around the borehole provide a favourable geometry for mapping both steeply and gently dipping structural features. The quality of the VSP data was very good and in many cases the same reflectors have been interpreted in all surveys. The HSP raw data is of a more modest quality, mostly due to the higher cultural noise and to the absorbing effect of the soft deposits at the bottom of the pond. However, after processing the HSP data displays the same reflector orientations as the VSP data and a cohesive model can be constructed. For all surveys and all the 60 profiles measured, most of the reflected energy seems to arrive from 330–355 degrees cloc2wise from North Ndip directions 150–175 degreesO with dips of 18–43 degrees. Another prominent orientation is dip direction 250–270, dips 50–87 degrees. The number of shot points increased from five to ten per survey, made possible by the use of the VIBSIST 1000 source instead of eYplosives, has definitely paid bac2 in terms of improved coverage and decrease of uncertainty related to the interpretation of the reflectors. Moreover, the increased precision in orientation resulting from the larger number of offsets and azimuths lead to a combined model more cohesive than obtained with earlier surveys.

Avainsanat - Keywords Reflection seismics, VSP, HSP, borehole surveys, 3-D interpretation, Image Space filtering, IP migration, modelling, SIST-sources ISBN ISBN 951-652-115-0

ISSN ISSN 1239-3096

Sivumäärä � Number of pages 115

Kieli � Language /nglish

LAAJENNETTU TIIVISTELMÄ

jatkuu

Tekijä(t) � Author(s) Calin Cosma, Nicoleta /nescu, /ric2 Adam, Lucian Balu Vibrometric Oy

Toimeksiantaja(t) � Commissioned by Posiva Oy

Nimeke � Title

S/ISMIS/T VSP- eA HSP-THTKIMHKS/T OLKILHODOSSA 2001

Tiivistelmä � Abstract Seismisif VSP NVertical Seismic ProfilingO Ra HSP NHorizontal Seismic ProfilingO -tut2imu2sia tehtiin vuonna 2001 /uraRoen Ol2iluodon tut2imusalueella. VSP-tut2imu2set tehtiin nelRfssf 2airanreifssf 2fyt-tfen 2ymmentf lfhdepistettf 2uta2in rei2ff 2ohti. Kahden HSP-linRan vastaanottimet siRoitettiin Korven-suon te2oaltaan pohRalle Ra 2ymmenen lfhdepistettf siRoitettiin altaan ympfrille. Vastaanottimina 2fytettiin VSP-tut2imu2siin 3-2omponenttista geofoni2etRua Ra HSP-tut2imu2siin hydro-foni2etRua. Kai22i mittau2set tehtiin 2fyttfen VIBSIST-1000 -lfhdettf rfRfhteiden asemesta. Lfhteen SIST-te2nii22a NSwept Impact Seismic ToolO 2fyttff aRan suhteen haRautettua is2usarRaa Npyyh2fisyfO elastisen energian tuottamiseen. Seismiset signaalit tuotetaan nopean is2usarRan avulla. Is2uRen vfleRf muutetaan mono-tonisesti siten, ettf syntyy aRallisesti ei-toistuva pulssisarRa. Lfhteenf VIBSIST-1000 2fyttff tra2toriin asennettua hydraulista pur2uvasaraa, Ron2a energiaa Ra is2utiheyttf sffdetffn tieto2oneella, servo-ohRatun hydraulisen virtaussfftimen avulla. Standardia ra2ennuste2nistf laitetta 2fyttfmfllf on voitu varmistaa ettf VIBSIST-lfhteet ovat turvallisia, ainetta ri22omattomia Ra ympfristgystfvfllisif. Siten menetelmf on mygs luotettava Ra 2ustannusteho2as. Kfytetty uusi VIBSIST-lfhteen signaalit ovat energiatasoltaan verrattavissa rfRfhteiden tuottamiin. VIBSIST on rfRfhteitf stabiilimpi, mutta sen suurimmat edut ovat lfhdepisteiden valmistelun matalat 2ustannu2set Ra tut2imusten toteutu2sen nopeus. HeiRastus2ulmien laaRa vaihtelu, pai2alliset heiRastavuuden erot, Ra yleisesti 2iteisen 2iven siirro2sista Ra ri2-2onaisuusvyghy22eistf syntyvft suhteellisen pienet seismiset vasteet vaativat teho2asta aineiston 2fsit-telyf. Kfsittelyn ensimmfisessf vaiheessa 2fsittelyrutiinein 2es2itytffn poistamaan suorat P- Ra S-aallot, put2i-aallot Ra maa2errosten Ra2sollinen tfrinf Nground-rollO, siten ettf hei2ommat, myghemmin ilmenevft viri2-2eet NheiRastu2setO saataisiin esille. Toinen vaihe 2oostuu pffosin IP-suodatu2sesta NImage Point, ns. KuvapisteO, Rolla pyritffn 2asvattamaan heiRastuneiden aalto2enttien nf2yvyyttf Ra erottamaan eri suuntaisten heiRastaRien synnyttfmif viri22eitf toisistaan. hs2ettfin 2ehitettyRf 2fsittely- Ra 2uvantamismenetelmif, 2uten useissa rei]issf VSP-tut2imu2sin havaittu-Ren ra2ennepiirteiden samanai2aista suuntau2sen tul2intaa, se2f IP-aalto2enttfmigraatiota, on hygdynnetty laaRasti ensimmfistf 2ertaa tfssf tygssf. HeiRastaRan imer2ittfvyyttfj voidaan arvioida 2fyttfmfllf sen ominaisuu2sien pysyvyyttf eri lfhdepisteiltf mitatuissa profiileissa, mi2f voidaan tul2ita osoitu2sena heiRastaRien laaRuudesta Ra Rat2uvuudesta tilavuu-den suhteen.

Posiva-raportti � Posiva Report Posiva Oy FIN-27160 OLKILUOTO, FINLAND Puh. 02-8372 (31) � Int. Tel. +358 2 8372 (31)

Raportin tunnus � Report code

POSIVA 2003-01 Julkaisuaika � Date

Maalis2uu 2003

LAAJENNETTU TIIVISTELMÄ

Tul2innat on tehty yhdistellen intera2tiivista mallintamista Ra IP-migraatiota. Mallinnusta 2fytettiin arvioi-taessa sel2eimpien, suurimmassa osassa profiileRa 2attavasti esiintyvien heiRastaRien NjpffheiRastaRienjO si-Raintia Ra asentoa. IP-migraatiota 2fytettiin testattaessa uutta menetelmff, Rossa pyrittiin tul2itsemaan pff-heiRastaRien 2anssa samoihin suuntausluo22iin 2uuluvien, hei2ommin erottuvien heiRastaRien siRaintia. VSP-menetelmf on todettu erityisen soveltuva2si 2iteisen 2iven seismisiin tut2imu2siin, Roissa seismiset lfhteet siRoitellaan maanpinnalle 2attavasti eri suuntiin 2airanreifn ympfrille. Tfmf tuottaa 2fyttg2elpoisen tut2imusgeometrian se2f Ryr22f- ettf loiva2aateisten ra2ennepiirteiden 2artoittamiseen. VSP-aineiston laatu on ollut erinomaista, Ra useissa tapau2sissa samat heiRastaRat on voitu tul2ita 2ai22ien rei2ien mittau2sista. HSP-datan laatu on vaatimattomampaa, lfhinnf voima22aan sivilisaatiohfirign vuo2si, Ra 2os2a te2oaltaan pohRalla siRaitsevat pehmeft maa2erro2set vaimentavat aaltoenergiaa. Aineiston 2fsitte-lyn tulo2sena HSP-tulo2sista voidaan 2uiten2in todeta vastaavat heiRastaRasuuntau2set 2uin VSP-aineistosta, Ra yhtenfinen malli on mahdollista laatia tulosten perusteella. Kai22ien rei2ien Ra linRoRen tut2imu2sista, Ra Ro2aisesta 60 mitatusta profiilista, suurin osa heiRastusenergi-asta nfyttff saapuvan 330–355 asteen suunnasta pohRoisesta mygtfpfivffn 2atsottuna N2aadesuunnat 150– 175 astettaO. Kaade vaihtelee vflillf 18–43 astetta. Toinen sel2ef suuntaus ovat 2aadesuunnat 250–270 as-tetta. Kaade vaihtelee vflillf 50–87 astetta. Lfhdepisteiden mffrff on lisftty ai2aisemmista viidestf pisteestf 2ymmeneen 2uta2in rei2ff tai linRaa 2oh-ti, min2f on mahdollistanut VIBSIST 1000 -lfhteen 2fyttg rfRfhteiden asemesta. Tfmf on ehdottomasti parantanut tut2imusten 2attavuutta Ra vfhentfnyt heiRastaRien tul2innan epfvarmuutta. Lisf2si heiRastaRien suuntaustiedon 2asvanut tar22uus, Ro2a on seurausta useammista 2fytgssf olleista lfhdepisteiden etfisyy2-sistf Ra siRaintisuunnista, on mahdollistanut eri rei2ien yhdistetyn mallin laatimisen. Mallin piirteet ovat yhtenfisempif 2uin ai2aisempien tut2imusten tulo2set. Avainsanat - Keywords HeiRastusseismii22a, VSP, HSP, rei2ftut2imu2set, 3-ulotteinen tul2inta, 2uvapistesuodatus, 2uvapiste-migraatio, mallintaminen, SIST-lfhdete2nii22a

ISBN ISBN 951-652-115-0

ISSN ISSN 1239-3096

Sivumäärä � Number of pages 115

Kieli � Language /nglanti

1

TABLE OF CONTENTSpage

Extended abstractLaajennettu tiivistelmä1 Introduction ........................................................................................................................... 32 Recording the HSP and the VSP seismic data.................................................................... 5

2.1 The survey layout ............................................................................................................ 52.2 The field equipment ...................................................................................................... 11

2.2.1 Seismic Source – VIBSIST 1000 .......................................................................... 112.2.2 Seismic Receivers ................................................................................................. 122.2.3 The Recording station ........................................................................................... 14

2.3 Quality control............................................................................................................... 152.3.1 Cultural noise ........................................................................................................ 15

3 The SIST Concept - Decoding of the VIBSIST records................................................... 173.1 The SIST concept .......................................................................................................... 173.2 Decoding of the VIBSIST signals ................................................................................. 20

3.2.1 Data processing – Noise reduction........................................................................ 204 Processing of the VSP data ................................................................................................. 23

4.1 Data quality and frequency analysis ............................................................................. 234.2 Preconditioning of the data profiles .............................................................................. 244.3 Rotation of horizontal components ............................................................................... 254.4 Velocity determinations................................................................................................. 28

4.4.1 Borehole OL-KR6 ................................................................................................. 284.4.2 Boreholes OL-KR7, OL-KR11 and OL-KR12 ..................................................... 31

4.5 Tube wave suppression ................................................................................................. 314.6 Suppression of direct P-wave and S-waves .................................................................. 324.7 Amplitude compensation and equalization ................................................................... 324.8 Image Point Filtering..................................................................................................... 34

4.8.1 Reflector enhancement in the image space ........................................................... 345 Processing of the HSP data................................................................................................. 37

5.1 Preconditioning of the signal ........................................................................................ 375.1.1 Down-going wave removal ................................................................................... 385.1.2 Velocity determination and refraction statics ....................................................... 38

5.2 Image Point Filtering..................................................................................................... 395.3 IP Migration................................................................................................................... 40

6 Interpretation of the VSP measured data from boreholes OL-KR6, OL-KR7,OL-KR11 & OL-KR12 ....................................................................................................... 45

6.1 3D interpretation of reflector elements from borehole OL-KR6.................................. 476.2 3D interpretation of reflector elements from borehole OL-KR7.................................. 516.3 3D interpretation of reflector elements from borehole OL-KR11 ................................ 566.4 3D interpretation of reflector elements from borehole OL-KR12 ................................ 62

7 Interpretation of the HSP data from lines HSP7 and HSP8........................................... 677.1 3D interpretation of reflector elements from line HSP7............................................... 677.2 3D interpretation of reflector elements from line HSP8............................................... 74

8 Combined Interpretation of all VSP and HSP data ......................................................... 818.1 VSP / HSP Multi-Profile Reflector Fitting ................................................................... 818.2 Integrated Site Model Based on the VSP & HSP Seismic Data ................................... 83

9 Conclusions .......................................................................................................................... 87

2

References .................................................................................................................................... 89APPENDICES ............................................................................................................................. 91APPENDIX A. Image Space Transform .............................................................................. 93APPENDIX B. IP Migration and the 3-D CDP Transform ............................................... 95APPENDIX C. Data plots from HSP7: High & Low dip IP Migration ........................... 97APPENDIX D. Data plots from HSP8: High & Low dip IP Migration ......................... 107

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! "NT#O$%CT"ON

The Vertical Seismic Profiling NVSPO and Horizontal Seismic Profiling NHSPO surveys were parts of the detailed site investigation programme for the final disposal of spent nuclear fuel, conducted by Posiva Oy. Site investigations were conducted by Vibrometric Oy during 2001 at the Ol2iluoto site in /uraRo2i, Finland. Two HSP lines were measured during May – eune, with receivers laid on the bottom of an artificial pond NKorvensuon Te2oallasO and ten source points Nfor each of the HSP linesO located around the pond. VSP investigations were carried out during eune – euly in boreholes OL-KR6, OL-KR7, OL-KR11 and OL-KR12. Ten shot points were used for each of these boreholes. The processing and interpretation of the results were completed during February 2002. VSP has eYtensively been used, over the past 15 years, for mapping fractures and fracture zones with various hard roc2 applications, from nuclear waste disposal NCosma et al., 2001aO, to ore delineation NKes2inen et al., 1999O, and to roc2 engineering NKes2inen et al., 2000O. Fracture zones in hard roc2 display wea2 seismic contrast and reflected wavefields are easier identified by increased coherency along time-depth paths corresponding to possibly real reflection events than by amplitude standout NCosma, 1995, 1990O. The VSP method has been found particularly suitable for surveys in hard roc2s NCosma et al., 2001bO, where receiver arrays placed in boreholes and sources spread on the surface at diverse azimuths around the borehole provide a favourable geometry for mapping both steeply and gently dipping features. Receivers located in the bedroc2 minimize the loss of resolution due to near-surface signal absorption. Recent surveys Neuhlin et al., 2002, Cosma et al., 2002aO, including the one at Ol2iluoto in 2001, have been carried out with a time-distributed swept-impact source, the VIBSIST N/nescu and Cosma, 1999k Cosma and /nescu, 2001cO, instead of eYplosives. Zith this source, the seismic signals are produced as rapid series of impacts, the impact intervals being monotonically increased to achieve a non-repeatable sequence. As the energy is built up from a large number of relatively low-power impacts, the high frequency components of the seismic signal are maintained. Methods developed over past 10 years NCosma et al., 1994a, 1994bk Hei22inen et al., 1994, 1995O and recently summarized in NCosma and /nescu, 2002bO were used for the processing and interpretation, e.g. the interactive determination of the orientation of the fracture zones Nreflecting planesO using simultaneously several VSP boreholes and 3-D wavefield migration.

"#

Faults, fracture zones, dissolution features and lithological contacts may all reflect seismic waves. The fracture zones display a relatively wea2 seismic contrast and eYtensive processing is needed to retrieve the reflected wave field from the seismic profiles and the information on the position of the reflectors. The data processing focuses first on eliminating tube-waves and direct P and S onsets. Median and band-pass filters are used for this purpose. The amplitudes are then equalised. The second stage of processing consists mainly of Image Point NIPO filtering techniques, aimed at enhancing the reflected wavefields and at separating events generated by reflectors with different orientations. Zith the IP transform, introduced by NCosma, 1990, Cosma and Hei22inen 1996O, stac2ing is performed along hyperbolic paths corresponding to the time-depth functions of possible reflectors. Due to this jnaturalj choice of the stac2ing paths, the coherency can be used effectively to enhance the wea2 reflections. Polarization analyses of hard roc2 data may be unstable because of criss-crossing reflection events and non-coherent scattering noise NCosma and /nescu, 2002bO. The stability increases in the IP space because the energy reflected on interfaces with different orientations accumulates in different regions of the IP space. The orientation estimates obtained by polarization analysis are improved by concurrent processing of several profiles. Zhen all the profiles have been processed and the reflection events emphasized by IP filtering, the positions and 3-D orientations of the reflectors are determined. Automatic interpretation procedures are used in order to diminish, whenever possible, the subRectivity of the interpretation.

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&,! !"#$%&'(#)$*+),&-$$ The seismic investigations carried out during year 2001 included VSP surveys in boreholes OL-KR6, OL-KR7, OL-KR11 and OL-KR12 and HSP surveys along two lines laid on the bottom of an artificial pond, the Korvensuon Te2oallas Nsee %&'()*+#2,1 and 2,2O. The VSP boreholes had been made by the diamond NcoreO drilling. The size of all holes has been 56 mm, eYcept OL-KR6, which is 76 mm wide. Ten shot points were used for each VSP receiver borehole and each HSP profile. The recording was done from all shots before moving the receivers along the line/borehole. # The starting directions and positions of the VSP boreholes in site coordinates are given in -./0*#2,1. The VSP survey configurations are given in -./0*#2,2. The coordinates of the shot points used for each VSP borehole are given in -./0*#2,!, -./0*#2,", -./0*#2,$ and -./0*#2,1. The positions of the HSP lines are given in -./0*#2,2. The coordinates of the shot points used for the HSP lines are given in -./0*#2,3, where the zero-offset Nnearest to the borehole topO shot point for each survey is printed bold.

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OL-KR6

6793045.6

1525931.5

2.28

40.0

36.0

6793352.9

1526128.6

-467.20

OL-KR7

6792118.1

1525558.9

9.54

20.5

43.0

6792311.5

1525680.3

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6792633.8

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310.0

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1526132.9

-756.62

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SP14 6792899 1525850.7 5

SP24 6792865 1526214.2 6

SP34 6792968 1525884.1 2.8

SP35 6793056 1525935.3 2.5

SP36 6793148 1525857.3 3.9

SP37 6793076 1526014.6 3.5

SP38 6793110 1526045 4

SP39 6793216 1526052.5 4.3

SP40 6793280 1526091.4 4.8

SP41 6793065 1526180.9 7

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SP11 6792242 1525863 9.6

SP16 6792397 1525423.2 8

SP17 6792361 1525455.7 8

SP18 6792425 1525583.2 10

SP19 6792287 1525561.8 8

SP20 6792231 1525674.7 8

SP21 6791979 1525885.4 9

SP22 6792143 1525540.3 10

SP23 6792087 1525498.7 9

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SP24 6792865 1526214.2 6

SP25 6792981 1526376.3 6

SP26 6793062 1526483.9 8

SP27 6792915 1526600.3 8

SP28 6792816 1526714.4 8

SP29 6792790 1526776.1 7

SP30 6792604 1526763.6 5

SP31 6792605 1526909 6

SP32 6792559 1526652.7 5

SP33 6792272 1526425.1 9

#####

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SP2 6792588 1525911.6 9

SP3 6792573 1526092.6 7

SP4 6792490 1526247 8

SP6 6792330 1526448 10

SP10 6792424 1525841.9 8

SP11 6792242 1525863 9.6

SP12 6792572 1525831.8 6.5

SP13 6792653 1525884.5 7

SP14 6792899 1525850.7 5

SP15 6792695 1526070.7 7

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for the HSP

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Northing l NmO

/asting m NmO

/levation B NmO

Northing l NmO

/asting m NmO

/levation B NmO

HSP7 6792402.10 1526450.39 6.99 6792476.08 1526101.08 6.93

HSP8 6792462.46 1526089.74 6.37 6792197.30 1526329.20 7.00

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SP1 6792535.2 1525906 8 outcrop NgneissO

SP2 6792588 1525911.6 9 outcrop NgneissO

SP3 6792573.2 1526092.6 7 outcrop NgraniteO


SP5 6792459.6 1526388.8 10 on road NcompactO


SP7 6792231.6 1526398.1 10 outcrop NgraniteO

SP8 6792186.5 1526299.9 10 on road NcompactO

SP9 6792290 1526142.1 10 on road NlooseO

SP10 6792423.8 1525841.9 8 outcrop NgneissO # The distances from the top of the boreholes to shot points used for the VSP surveys range from 10 to 335 m for OL-KR6, 30 to 415 m for OL-KR7, 30 to 585 m for OL-KR11 and 40 to 555 m for OL-KR12. The maYimum distances from shot points to deepest receivers in the boreholes range from 710 to 1135 m. The range of distances between shots and receivers for the HSP surveys is 70 to 570 m. The perspective view of the layout of source points, receiver lines and boreholes is shown in %&'()*#2,2.

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56567$ 8#/%3/9$8,&'9#$:$;<=8<8!$7>>>$ An engineered seismic source, the VIBSIST-1000, was used for both the VSP and HSP surveys. The VIBSIST-1000 is based on the Swept Impact Seismic Technique NSISTO described in Section 3 NCosma and /nescu, 2001ck Par2 et al., 1996O. The VIBSIST-1000 source uses a tractor-mounted hydraulic roc2-brea2er, powered through a computer controlled flow regulator. The Ol2iluoto surveys were performed with a brea2er model Rammer S-22, mounted on a 15-ton eYcavator ?%&'()*#2,!I and delivering 600-1000 e/impact at 500-1000 impacts/minute. The operating pressure has been 80-130 bar. The computer-controlled flow regulator, command equipment and software were built by Vibrometric. The hydraulic control produced a sweep of about 120 impacts in a period of 18 s. A pilot signal was recorded from a geophone placed near each shot point. Hsing standard construction equipment ensures that the VIBSIST sources are safe, non-destructive and environmentally friendly. This also ma2es the method reliable and cost effective. The source coupling was influenced by the variable ground conditionsV outcrops usually provided good seismic records NeYcept for shot point SP10O while those acquired using a metal plate on a more or less compacted road bed generally produced less seismic energy. A larger number of sweeps Nup to 10O was used to compensate for the poorer ground conditionsk with this approach interpretable data was acquired at each shot location. To allow the mapping of structures dipping in various directions, the shot points were located at various azimuths around the VSP boreholes and the HSP lines NThe distances from the top of the boreholes to shot points used for the VSP surveys range from 10 to 335 m for OL-KR6, 30 to 415 m for OL-KR7, 30 to 585 m for OL-KR11 and 40 to 555 m for OL-KR12. The maYimum distances from shot point to deepest receivers in the boreholes range from 710 to 1135 m. The range of distances between shots and receivers for the HSP surveys is 709 to 570 m. The perspective view of the layout of source points, receiver lines and boreholes is shown in %&'()*#2,24#

12#

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56565$ 8#/%3/9$?#9#/(#'%$$ Two different receiver chains were used for the VSP and HSP surveys at Ol2iluotoV a 3-component geophone chain Nthe R8-lmB-CO for the VSP measurements and a hydrophone chain Nthe TC-30O for the HSP measurements. -;*#K&/)5O*:)&=#E3,UVW,Q#Z*56;5>*#=;.&>## The R8-lmB-C geophone chain is equipped with 24 28-Hz geophones placed in eight 3-component modules N%&'()*#2,"O. The z-component is directed along the hole and the Y- and y-components are perpendicular to the z-component and to each other. The distance between the modules is five meters. The geophone chain contains also a down-hole preamplifier for each channel. The gain of the amplifiers is fiYed at 34.2 dB. The frequency range is from 40 to 1000 Hz. The overall sensitivity of the geophone-amplifier combination is 133 V/cm/sec. The units are equipped with side arms for clamping, activated by DC motors. The clamping control is independent for each unit.

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-;*#K&/)5O*:)&=#-Q,!S#H<G)56;5>*#=;.&>## The TC30, seen in %&'()*#2,$., consists of 30 water-coupled piezoelectric transducers with a cylindrical sensitivity characteristic. The distance between the modules is 2m. The frequency range is from 10 to 15000 Hz. A receiver module is shown in detail in %&'()*#2,$/4# /ach module consists of two ring-shaped piezoceramic elements and a 40 dB preamplifier. A high-density gel is used as bac2fill material and a low-density epoYy compound is inRected between the piezoceramic elements and the cover. This construction provides a high transverse acoustic sensitivity, through the large active area of the crystals, while diminishing the disturbing influence of the tubewaves, when the tool is used in a borehole. The construction of a TC-30 module is shown in %&'()*#2,$=.

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5656@$ !"#$?#9,'0/4A$%-+-/,4$ A PC-based acquisition system was used N%&'()*#2,1O, consisting of an ICS 32-channels, 24-bits acquisition board, with LabView based acquisition interface.

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The PC-based solution has been chosen instead of a standard 24-bit seismograph because of the unusually long records needed N100,000 samples/channel for a 20 s sweep at 0.2 ms sampling rateO, which is unavailable with standard seismographs. The custom-written software allows concurrent signal processing, needed for on-line chec2ing of the signal quality. The decoded seismic record is built by 32-bit stac2ing of approYimately 1000 individual pulses. Details on the SIST technique are given in Section 3.1. The data is recorded on an internal hard dis2 in the ACH Vibrometric format.

&,- B&+*/-)$9,4-',*$ The required number of sweeps used at each shot point was continuously re-evaluated as the survey progressed. The standard quality control procedure consisted of evaluating the signal-to-noise ratio of the first sweep and based on this observation a choice of 5 or 10 sweeps was determined. The quality control procedure also included the inspection of the last sweep recorded to ensure that the equipment had functioned properly. The number of sweeps was also increased as a function of the shot-receiver distance.

56@67$ C&*-&'+*$4,/%#$ During the survey, annual maintenance wor2 on one of the nuclear reactors resulted in a compleY electrical noise with two out-of-phase contribution from each of the two reactors. This noise was pic2ed up by the receivers and cables and was particularly strong during the first days of the HSP survey. In the presence of strong electrical noise, 10 sweeps were recorded for each shot location, since the data quality was difficult to evaluate without the use of a time consuming filtering algorithm. /lectrical noise was also present when the acquisition system was powered from the local 220 V networ2. Zhen powered using a portable generator properly grounded to the recording cabin, the electrical noise level was reduced significantly. Diamond drilling between shot locations 1 and 10 during the HSP survey was unnoticed and does not seem to appear on the seismic records. Zind noise and rain were not a problem during the survey. Spurious mechanical noise and noise generated by vehicle traffic do not represent a problem for the quality of the seismic data, as these types of noise are cancelled out through the stac2ing procedure used for the deconvolution of the long VIBSIST sweeps.

12#

- T(E S"ST CONCE)T . $ECO$"N' OF T(E *"BS"ST #ECO#$S

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The seismic signals are produced as series of pulses, according to a specific pre-programmed sequence, which ma2es the system similar to Vibroseis. However, the use of the monotonous variation of the impact rate controls effectively the non-repeatability of the impact intervals and achieves a wide bandwidth even when the coupling to the roc2 or ground is relatively poor.

The principle of the VIBSIST sources is eYplained through the following synthetic eYample. %&'()*# !,1 depicts a 20-level portion of a synthetic VSP profile. The data contains the down-going direct wave field and three up-going reflection events. The shape of the source wavelet, the position and the relative amplitude of the reflection events have been modelled after a real VSP survey conducted with eYplosives. Hnli2e the real records, the synthetic traces contain only the four elements mentioned above Ndirect wave and three reflectionsO but no bac2ground noise, scattering or converted wave modes of any 2ind.

"#$%&'! 0)*4# RB.O60*# 59# .# +<>:;*:&=# K@A# 6)59&0*C# G58>,'5&>'# .>G# (6,'5&>'#8.7*#9&*0G+4# -;*# G.:.# =5>:.&>+# :;*# G58>,'5&>'# G&)*=:# 8.7*# 9&*0G# .>G# :;)**# (6,'5&>'#)*90*=:&5>#*7*>:+#?.:#1SSC#12$#J#11S#O+#95)#9&)+:#)*=*&7*)I4#

The time series in %&'()*#!,1 can be written symbolically asV

s1NtO n sNtO o eNtO ?#!,1#I

where +?:I is the source signature, *?:I is the earth impulse response, o is the convolution operator.

13#

A similar set of records obtained by a VIBSIST source would loo2 li2e shown in %&'()*#!,2.

"#$%&'!0)(4#M5>'#+<>:;*:&=#KXY@X@-#)*=5)G4# Compared with %&'()*#!,1, the VIBSIST records in %&'()*#!,2 are longer Nto depict this feature the horizontal aYis has been compressedO. The VIBSIST records consist of a large number Nnormally 100 to 1000O of impacts produced at monotonously varying time intervals. This can be written asV

s2NtO n !NtO o s1NtO ?#!,2#I

where +1?:I###is given by equation N3-1O and

!?:I is the VIBSIST time impact sequence. Hnli2e with synthetics, in the real case, the noise cannot be neglected. Therefore, the data from %&'()*#!,2 would loo2 more li2e shown in %&'()*#!,!.

"#$%&'!0)04#M5>'#+<>:;*:&=#)*.0,0&9*#0&F*#KXY@X@-#)*=5)G4#

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The recorded signal can be eYpressed asV

)=?:I n +2?:I p >?:I ?#!,!#I#

where +2?:I###is given by equation N3-2O and#>?:I is the added wide-band noise.

The 2ey idea of the SIST concept is to compute the time functionV

)G?:I#\#!?:I"#)=?:I#\#]Q%^!?:I_`#+1?:I#a!?:I`>?:I# # # # # # ?#!,"#I#

where

]Q%#is the autocorrelation operator, and "#is the deconvolution operator.

One should note in the eYpression above that the second term !?:I`#>?:I tends to zero, as random noise tends to get cancelled through correlation. It follows thatV

if## ]Q%?:I n 1#at#t n 0#and#ACFNtO n 0 elsewhereC### # # # ?#!,$#I#

then )G?:I n +1?:I

In other words, the VIBSIST and the single-pulse signals will become similar, with the benefit on the VIBSIST of allowing noise cancelling. The result of the operation described above is shown in %&'()*#!,", which is indeed very close to the noise-free synthetic profile of %&'()*#!,1.

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@6567$ D+-+$2',9#%%/4A$:$E,/%#$'#0&9-/,4$ The electric noise level was found to be relatively high, especially during the HSP survey, the main components being contamination with 50 Hz power frequency and harmonics and occasional spi2es and noise bursts. Q5>:.O&>.:&5>#8&:;#$S#Hb#658*)#9)*[(*>=<#.>G#;.)O5>&=+## The most li2ely reason for the high contamination is the proYimity of the power plant and lines, but alterations to the receiver chains and recording equipment to ma2e them less sensitive to electric noise may be considered in the future. The frequencies of the harmonic disturbances are within the band of the useful signal and cannot be removed by band-pass filtering. Intricate procedures were devised in order to reduce the noise effectively. A data-adaptive time-domain notch filter was used to eliminate the harmonic disturbances. The application of the notch before the auto-correlation of the sweep was found to be more effective than after the auto-correlation. c&G*,/.>G#/.=F')5(>G#>5&+*# Zith the VIBSIST sources, random noise components are effectively eliminated by auto-correlation, as eYplained in Section 3.1. The same is not possible with single impact sources and eYplosive sources rely on the high energy delivered to provide a good signal-to-noise ratio. The spectra changed somewhat, compared with their non-correlated versions, due to the suppression of the wide-band noise. Readable seismograms clearly emerge also in time domain. P5&+*#/()+:+# Noise bursts, of both acoustic and electric origins, may appear during the recording of long sweeps. The common auto-correlation performed by summing with various time lags may be offset by such events, if their amplitude is sufficiently large. In these conditions, median techniques lead to better and more stable signal estimates. An alpha-trimmed median estimator was used instead of the average NBednar and Zatt, 1984O.

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Q5))*0.:&5>#>5&+*# A condition used with the eYample given in the Section 3.1 has been that the auto-correlation function of the VIBSIST sweep is negligible for all time lags eYcept :#\#S. Consequently, the intervals between the impacts must be very well controlled to never be the same throughout the whole VIBSIST sequence. This level of control may be difficult to achieve with mechanical devices and corrective-processing schemes must be applied. %&'()*#!,$.#shows a VIBSIST signal sequence recorded by the pilot geophone adRacent to the source. The time aYis has been strongly compressedk hence, the individual impacts are not visible. Zhat is visible is that the amplitude of the impacts varies significantly along the sweep. Zere this behaviour of the source not to be corrected, the higher impact frequencies towards the end of the sweep would be overpowering the low impact frequencies from the beginning of the sweep, where the hydraulic device runs at low power. %&'()*# !,$/ displays the corrected command sequence, where a 5th order polynomial fit has been used on the raw sequence. The inverse polynomial function has been used to bring all amplitudes to roughly the same level.

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%&'()*#!,$= and %&'()*#!,$G display the autocorrelation functions NACFO of the raw and corrected sweeps, respectively. One should note that the plots are displayed within a vertical range of p/-0.1, i.e. only one tenth of the full range of the ACF is shown. The conclusion is that a cleaner ACF is obtained by balancing the energy of the impacts. The result of a clean ACF is the elimination of the correlation noise appearing as a spurious repetition of the real seismic events earlier or later in the seismograms. Such artefacts can be seen in %&'()*# !,1# ?0*9:I, obtained by straight correlation. The same profile on which the balanced energy correction has been applied is presented in %&'()*#!,1 ?)&';:I.

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/ )#OCESS"N' OF T(E *S) $ATA The reflecting interfaces in hard roc2 usually display a relatively wea2 seismic contrast. These are mostly faults, fracture zones and contacts between roc2 types. /Ytensive processing is needed to retrieve the reflected events from the seismic profiles and the information on the position of the reflectors. The processing sequence aims to improve the signal-to-noise ratio, so that the later events, e.g. reflections, become visible. As the reflection coefficients are generally low, the reflectors cannot normally be identified by an amplitude standout. Phase consistency has been found to be a more sensitive indicator NCosma and /nescu, 2002bO. The first stage of the processing sequence focuses on eliminating such wave-fields as the direct P, direct S, tube-waves and ground-roll, so that the wea2er later events, e.g. reflections, become visible. In this stage, the direct wave fields and other coherent disturbances are removed by slant median filtering and the signal levels are adRusted in such a way that the amplitudes of different traces and different parts of the same trace become comparable. The second stage of the processing sequence consists ofV

#$ Pic2ing of the first arrival times and velocity analysisk

#$ Rotation of the horizontal components to radial and transverse, where iradialj stands for the direction perpendicular to the hole and pointing towards the source and itransversej for the direction perpendicular to the radial and to the holek

#$ Image Space NIPO processing is done to enhance the reflected wave fields and

separate reflection events originating at interfaces with different orientations Na description of Image Space technique is given in AppendiY AO.

Once all the profiles have been processed and the reflection events emphasized, the positions of the reflectors are determined by interactive interpretation. However, increasingly compleY automatic interpretation procedures are developed, the intention being to diminish whenever possible the subRectivity of the interpreter.

/,! D+-+$1&+*/-)$+40$.'#1&#49)$+4+*)%/%$ The data has been inspected for possible malfunctions of the measuring system, unusually high noise levels, possible errors in coordinates, time delays and trace order. At the end of this process all errors falling in the categories listed above were corrected.

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/,& F'#9,40/-/,4/4A$,.$-"#$0+-+$2',./*#%$$ The purpose of this processing stage is to include the geometry information to the data profiles, to band-pass filter the data in the frequency band of the seismic signal and to adRust the signal levels so that the average amplitudes of different traces and different parts of the same trace become comparable. The frequency band selected for the filter is as wide as possible, the reRected spectral components corresponding to clearly identified sources of noise. The frequency band of the P-waves was estimated to be 50 – 250 Hz. A zero-phase band-pass filter q50 - 250r Hz was used for filtering all data profiles. The frequency content of the recorded data is illustrated in %&'()*#",1, which displays the spectra of the data profile shown in %&'()*#",2.

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/,- ?,-+-/,4$,.$",'/G,4-+*$9,32,4#4-%$ The orientation of the horizontal components Nl and mO is not set or determined during the measurements and, due to the free rotation of the down-hole probes while changing position, the horizontal components show a poor trace-to-trace consistency in both amplitude and phase. The rotation of the horizontal components is done computationally, assuming that the direct P wave is polarized along the source-receiver line. The l-m trace pair is rotated so that after rotation the l component acquires the most possible of the P-wave energy and becomes the sRadials component, while the m component contains the minimum possible of the P-wave energy becomes the sTransversals component. The B-component remains directed along the borehole and it becomes the sAYials component. As an eYample, aYial and rotated radial and transversal components from OL-KR11 shot point SP28 are presented in %&'()*#",2, %&'()*#"," and %&'()*#",$. The location of source point and the borehole is presented in %&'()*#",!#below.

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H6H67$ =,'#",*#$IJKL?M$ The VSP investigations performed in 1995 in borehole OL-KR6 NHei22inen et al., 1995O, revealed unusual velocity variations with the depth and the azimuth of the shots. Anisotropy has been presumed as possible cause and the transversely isotropic model adopted succeeded in restoring normal velocity vs. depth functions. The 1995 surveys in OL-KR6 were conducted to a maYimum borehole depth of less than 300 m. The surveys carried out in 2001 too2 advantage of the eYtension of OL-KR6 and were carried out to a depth of nearly 600 m. #%&'()*#",1 shows the velocity vs. depth functions for the 2001 surveys. An odd behaviour of the velocity vs. depth functions, similar to the one observed in the 1995 surveys can be seen to a depth of approYimately 300 m. The velocities below 300 m are very similar for all profiles. The abnormal velocity field is therefore confined to shallow depths and heterogeneity can be the cause as well as true anisotropy. The anisotropic model derived in 1995 remains valid at shallow depths but not at larger depths and it is difficult at this time to decide whether the odd velocity behaviour is the effect of local anisotropy or local heterogeneity. Location of borehole and the shot points are shown in %&'()*#"424

"#$%&'!1)3/#K*05=&:<# 7+4#G*6:;# 9(>=:&5>+# 95)# :;*#1S#6)59&0*+#O*.+()*G# &>#/5)*;50*#LM,DE14#-;*#5+=&00.:&5>#&>G&=.:*+#.==().=<#59#:;*#:&O*#+.O60&>'#59#:;*#)*=5)G&>'4#

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!!"#$%&'!1)4/#M5=.:&5>#59#/5)*;50*#DE1#.>G#:;*#+;5:65&>:+4##%&'()*#",3 shows the tomographic velocity distribution obtained for the ten shot points and the 119 detectors, proRected on the vertical plane containing the borehole. A velocity of 5700 m/s is typical at the site in sparsely fractured roc2, a lower velocity, near the surface at the top of OL-KR6 could thus indicate the presence of crushed roc2. A low-high-low velocity alternance with depth can be observed, including a wedge-shaped higher velocity body, which can induce on the travel times effects similar with those of genuine anisotropy. %&'()*# ",T depicts the time residuals between the travel times computed with the tomographic velocity field of %&'()*# ",1 and the travel times corresponding to a constant velocity of 5450 m/s. The dependence of the time residuals with the depth along the hole is very stable for all profiles. The best fit function, shown as a line in %&'()*#",T has been used to derive and perform model-driven static corrections for all the ten measured profiles. The static corrections computed by tomography lead to well-behaved velocity vs. depth functions, both at shallow and larger depths.

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H6H65$ =,'#",*#%$IJKL?NO$IJKL?77$+40$IJKL?75$ The velocity fields for all profiles measured in boreholes OL-KR7, OL-KR11 and OL-KR12 showed no abnormal characteristics. The signal appears with delays comprised between -3 ms and p3 ms, but the delays can be eYplained by the variable roc2 conditions in the immediate vicinity of each source location and can be removed by standard static corrections. The interval velocities Nslope of the traRectory length vs. travel timeO remain for all shot points within p/- 100 m/s Np/- 2tO of the 5750m/s average.

/,0 !&P#$Q+(#$%&22'#%%/,4$$ Tube waves are generated when the geometry and/or the mechanical properties vary suddenly along water-filled boreholes e.g. the bottom of the hole, the water surface, fractures intersecting the borehole. Tube waves travel along the hole and can become a real nuisance when attempting to identify P- and S- reflections, as the tube wave amplitude does not decay due to geometrical spreading. An efficient way to eliminate the tube waves is by means of median filters ta2en along the slope corresponding to p/- the tube wave velocity. Because tube waves are generated in and travel along the hole, their apparent and real velocities are the same Nup to the p/- signO, producing straight patterns in the profile. Hp and down going tube waves were removed as described above, using a velocity window of 1350 – 1550 m/s.

!2#

/,1 8&22'#%%/,4$,.$0/'#9-$FKQ+(#$+40$8KQ+(#%$$ Direct P-wave arrivals are removed using similar median filtering techniques as for tube waves. The only difference is that, as far as direct P- Nor S-O waves are concerned, the traRectory along which median filtering is done is not straight, but follows the true travel time curve.

/,2 R32*/-&0#$9,32#4%+-/,4$+40$#1&+*/G+-/,4$$ Amplitude compensation NAFCO is performed to cancel the effects of geometrical spreading and attenuation and to reconstruct the original amplitude variations along the trace. Zithout amplitude compensation the reflected wavelets would be much wea2er than the direct arrivals. A variable gain operator is run along the records to increase the amplitude of later events assumed to have travelled along longer paths. The average amplitudes of the traces forming the profile are also equalized, for the same reasons. The amplitude compensation for all three components was done with the same operator, so that the amplitude ratio between the components is conserved after AFC. The pre-processed profiles from borehole OL-KR11, shot point SP28 are presented in %&'()*#",1S, %&'()*#",11 and %&'()*#",12. The suppression of the direct P- and S-waves and of the tube waves is evident. It can be also noticed that coherent reflection patterns start to be visible after pre-processing. Shotpoint location is shown in %&'()*#",!4

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/,3 <3+A#$F,/4-$S/*-#'/4A$$ The Image Point transform and related filtering techniques are described in AppendiY A. One of the properties of this transform is that, if the velocity field is correctly modelled, the coherent energy adds in phase, producing well-defined maYima in the IP NImage PointO space. This opens eYtraordinary possibilities for intricate processingk including e.g. enhanced polarization analysis, azimuth and dip filtering, as well as non-linear and neural networ2 based coherency-enhancement schemes.

H6T67$ ?#.*#9-,'$#4"+49#3#4-$/4$-"#$/3+A#$%2+9#$ The data shown in %&'()*# ",1!, %&'()*# ",1" and %&'()*# ",1$ as eYamples of IP processing are derived from the pre-processed profiles from %&'()*#",1S, %&'()*#",11 and %&'()*#",12, respectively. Shot point location is shown in %&'()*#",!4

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0 )#OCESS"N' OF T(E (S) $ATA The quality of the HSP data collected at Ol2iluoto in 2001 was variable. At times, compleY electrical noise was quite strong during the data acquisition and had to be removed prior to the correlation and stac2ing of the raw field records. The data quality was also affected by the source location and the ground conditions directly below the receivers. Signal quality variations along the HSP profiles are li2ely caused by overburden thic2ness changes and more severe attenuation could be related to zones of poorly compacted fill material while high-quality data may correlate with roc2 outcrops. Changes in frequency content from one shot point to the other most li2ely originate from the local conditions at the source location Ni.e. bedroc2, roadO or from geological structures located between the shot and the receivers.

0,! F'#9,40/-/,4/4A$,.$-"#$%/A4+*$ The correlation and stac2ing of the HSP raw field gathers was in a manner similar to the one used for VSP and described in Section 3.2. However, due to the higher variability of quality of the HSP data, an additional pre-processing sequence had to be interposed between the correlation of the sweeps and the Image Point processing scheme. The additional pre-processing sequence applied to the HSP data is outlined in -./0*#$,1.

+,-.'!2)*4#H@A#G.:.#6)5=*++&>'#+*[(*>=*4#

####A)5=*++&>'#@:*6# ####A.).O*:*)+#

Apply trace energy balancing NAFCO ZindowV 0.2 s

Spectral equalization Frequency bandV 20-200 Hz Number of bandsV 4 Operator lengthV 0.1 s

Median filter Nto remove first brea2sO Operator lengthV 31 traces

Linear moveout correction VelocityV 5185.4 m/s Time shiftV 0 s

Besides the operators listed, predictive and spi2ing deconvolution were tested, as potential means of improving the signal-to-noise ratio. However, the spectral equalization proved to be more robust. The frequency content analysis was performed by creating a series of band-limited sections. A total of 9 frequency bands were generated between 10 and 430 Hz. This analysis has shown that below 50 Hz, the HSP data is dominated by S-waves and ground roll with only wea2 P-wave first brea2s. Above 200 Hz, P-wave first brea2s are generally wea2 and noise dominates. Hence, most of the useful signal is found for frequencies between 50 and 200 Hz. The high frequency content of the data has been enhanced by spectral equalization. The algorithm used here is especially effective on seismic data with poor signal to noise ratio.

!3#

Spectral balancing is performed by computing the spectra in a number of frequency windows, to which an automatic gain control operator NAFCO is applied. The individually normalized frequency limited traces are then recombined to produce the spectrally equalized seismic trace.

U6767$ D,Q4KA,/4A$Q+(#$'#3,(+*$ The down direct P-waves were removed using a 31-trace median filter. Reverberations due multiple reflections occurring between the bottom of the pond and the water surface demanded the median filter to be run for the whole length of the records. In principle, this process might also remove possible reflection events nearly parallel to the P-wave first arrivals. However, the 31-trace wide median filter ma2es the accidental removal of true reflected energy very unli2ely.

U6765$ ;#*,9/-)$0#-#'3/4+-/,4$+40$'#.'+9-/,4$%-+-/9%$ A horizontal proRection of the velocity field in the area comprising the two HSP lines has been obtained by tomographic analysis. The tomogram, with the lines and shotpoints, is shown in %&'()*#$,14#Synthetic travel times were computed for each shot-receiver pair, using the velocity model from %&'()*#$,1#and used to perform the static corrections to a flat velocity of 5185 m/s. Note that the static-corrected velocity is not the same with the average velocity in the tomogram, which is 4035 m/s. The reason is that the tomographic velocity reflects the condition of the roc2 at surface, while the static corrections have been performed to match the roc2 properties to a depth of 200-300 m. The nearly North-South velocity pattern should be noted in support of the fracture model derived in Chapter 7 below. #

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0,& <3+A#$F,/4-$S/*-#'/4A$ The Image Point transform and related filtering techniques are described in AppendiY A. The processing sequence is illustrated on the profile from HSP line 8, Shot SP1 in %&'()*#$,2 through %&'()*#$,".

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0,- <F$V/A'+-/,4$$ The VSP and HSP data are essentially single-fold and thus standard migration techniques are not applicable. The IP migration process aims at producing sections through the earth with assumptions on the stri2e and dip of the reflectors derived from the 3-D geometrical fitting eYercise conducted on a few, most resolved, features ta2en to be representative for the classes of orientations to which they belong. In %&'()*#$,$ and %&'()*#$,1, the profile from %&'()*#$," has first been filtered to contain only reflection events compatible with the respective orientation of the IP migration. In the eYample given in %&'()*# $,2, the high-dip migrated profiles corresponding to the source SP1 for profiles HSP7 and HSP8 have been plotted together in their true positions in space coordinates. The power of IP migration as an interpretive aid can be appreciated in this representation.

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1 "NTE#)#ETAT"ON OF T(E *S) +EAS%#E$ $ATA F#O+ BO#E(OLES OL.4#15 OL.4#25 OL.4#!! 6 OL.4#!&

Due to the wide diversity of reflection angles, to the local variations of reflectivity and, generally, to the relatively wea2 seismic response of faults and fractured zones, which demands intensive processing, the \importance] of a reflector can not be reliably quantified based on the amplitude of the corresponding event in a time-depth profile. Consequently, the VSP profiles measured in crystalline roc2, tend to display a relatively numerous collection of reflection events with similar amplitudes. The proof of \importance\ of a reflector actually becomes a proof of its consistency amongst several profiles, which can in turn be interpreted as an indication of spatial eYtent and continuity. One should though note that each depth-time profile is a two dimensional representation and does not contain sufficient information for the complete determination of the 3-D orientation and position of a reflector. Several profiles need to concur to resolve the orientation problem. The reflector fitting procedure is interactive and consists of superposing travel time functions on the reflection events. The travel time curves are displayed as coloured lines in Image Point processed sections. The depth of intersection in the receiver borehole and a dip-stri2e function best fitting the chosen traRectory are calculated. The dip and stri2e are varied according to the relation given by the fit and displayed as a stereographic proRection. The dip and dip-direction are determined by fitting amongst at least three different profiles. In each profile, reflectors are classified in three categories. MaRor events, appearing as well defined Nstanding out by means of coherency and amplitudeO and continuous, belong to the first category Nmar2 n 2O. The wea2er reflectors, visible but overridden by stronger events of other orientations belong to the second category Nmar2 n 1O. If the position and orientation of an event are determined from other profiles but the event does not appear as visible in the current profile, it is categorised as a third class Nmar2 n 0O. The mean of the mar2s obtained in all profiles is then computed for each reflector. Reflectors obtaining mean mar2 larger than 1.0 Nthe absolute maYimum being 2.0O are classified as certain Nclass IO. Reflectors with mean mar2s between 0.5 and 1.0 are classified as probable Nclass IIO. The wea2 seismic structures with mean mar2s lower than 0.5 are classified as possible Nclass IIIO. The first column in -./0*+#141#,#14" is the event number, which is the same as the label of the reflector curves shown in %&'()*+# 141# ,# 142S and in the teYt. The event number is unique throughout the site model compiled from the VSP data and consistent with the one shown in -./0*#3414 The width of the reflective elements in 3D figures is 100 m, which corresponds to p/- two mean wavelengths. The second column is the depth of the reflector in the hole Nor the eYtension of the holeO. This parameter is relevant for interpretation for the reflectors actually intersecting the hole. For the others, it is only a reference depth, describing the position of the reflector

"1#

along the line of the borehole aYis. A reference depth iabove the groundj indicates reflector dipping outwards of the borehole aYis. The dip directions of the reflectors given in the third column and dips in the fourth column were determined interactively. This is done in several steps. Firstly, a reflector is identified in one profile by its outstanding amplitude/ coherency/ continuity. The corresponding hyperbolic travel time function is computed by clic2ing two points along the event. Secondly, the locus of the cruY points Nfoot of perpendicular to the plane going through a given originO is computed. As the profiles are 2-D, the 3-D positions of the cruY points still have one degree of freedom and the loci are closed curves in space and in fact they are circles. The point of minimum tension Nminimum mean distanceO amongst groups of cruY circles is then computed and ta2en as the cruY point, now fully determined, of the given reflector. The computations are then performed in an inverse order, to determine in each profile the travel time function for the reflection plane corresponding to the Rust determined cruY point. The neYt stage is to allow a variability in the fit, e.g. p/- half wavelength on each side of the predicted travel time function. The path of maYimum signal energy/coherency is determined automatically within the interval allowed. The fifth column presents the confidence class, as defined earlier in this chapter. The last column in the tables lists the boreholes in which the respective reflector has been identified. For all surveys and all the 60 profiles measured, most of the reflected energy seems to arrive from 330-355 degrees cloc2wise from North Ndip directions 150-175 degreesO with dips of 18-43 degrees. Another prominent orientation is dip direction 250 - 270, dips 50 -87 degrees.

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11 635 160 25 II KR11

15 749 224 65 I KR11

1 765 200 20 II KR11

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7 220 250 75 II KR12

18 223 170 8 III KR12

4 345 175 12 II KR12

24 398 255 78 II KR12

5 440 175 15 I KR12

11 628 160 25 II KR12

17 650 225 57 I KR12

25 700 180 5 II KR12

26 780 180 0 I KR12

9 790 260 70 I KR12

10 816 255 70 I KR12

1 856.5 200 20 II KR12

14 1005.5 175 20 II KR12

8 1038 226 52.5 III KR12

13 1071 225 62 II KR12

2 1180 220 55 III KR12

21 1347 245 53.5 III KR12

15 1504 224 65 I KR12

22 1526 225 55 II KR12

23 1898 261 67 II KR12

1!#

"igure 6-17. VSP KR12. Reflectors interpreted from SP02, located near the borehole top. Labels refer to Table 6-4 and Table 8-1. Shotpoint locations are presented in Figure 2-1, 2-2 and 6-22, and their coordinates are listed in Table 2-6.

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2 "NTE#)#ETAT"ON OF T(E (S) $ATA F#O+ L"NES (S)2 AN$ (S)3

The interpretation was made using a combination of the interactive modelling presented in Chapter 6 above and IP Migration. The modelling was used to estimate the positions and orientations of the maRor reflectors, found consistently in the maRority of the profiles. The IP Migration was used as a trial of a new methodology to allow the interpretation of less visible reflectors belonging to the same orientation classes as the maRor ones. The results are displayed on -./0*# 2,1 and 2,2C# and# %&'()*+# 2,2# through 2,11 below. The reflector numbers do not refer to the VSP reflector numbers shown in Chapter 6 and Chapter 8.

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M*>':;#.05>'#:;*#0&>*#?OI#

N&6#N&)*=:&5>#?G*'I#

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18 -4085 148 15 I 1,2,3,4,5,6,7,8 15 -3103 165 16.5 I 1,2,3,4,7,8,9,10 4 -6135 170 17 I 1,2,3,4,5,6,7,8,9,10

13 -1507 146 18 I 1,2,3,4,5,6,7,8,9 8 -5110 152 18 I 1,2,3,4,5,6,7,8,9,10

11 -2390 170 18 I 1,2,4,5,6,7,9,10 20 -4587 151 18.5 I 2,3,4,5,6,7,8,9,10 5 -3783 160 20 I 1,2,3,4,5,6,7,8,9

17 -4902 170 20 I 1,2,3,4,5,6,7,9,10 14 -1875 159 22 I 1,2,3,4,5,6,8,9,10 19 -5446 170 24 I 1,2,4,5,7,10 3 -3213 170 25 I 1,2,3,4,5,6,7,8,9,10

24 -1900 170 25.5 I 1,2,3,4,5,6,7,9 25 -2007 177 25.5 I 1,3,4,6,8,9,10 21 -50 127 29 I 4,5,6,7,8,9 2 -2512 170 30 I 1,2,3,4,5,6,7,8,9 9 -7600 173 30 I 1,2,3,4,5,6,7,8,9,10

16 -4140 176 30 I 1,2,3,4,5,6,7,8,9,10 7 -6607 180 30 I 1,2,3,5,7,8,9,10

22 -273 153 30.5 I 4,5,6,7,8,9 1 -2285 170 31 I 1,2,3,4,5,6,7,8,9,10

10 -7660 171 31 I 1,2,3,4,5,6,8,9,10 41 189 278 43.5 I 1,2,3,9,10 34 725 269 54 I 1,3,4,5,6,7,8,9 28 297.5 260 60 I 1,2,3,4,8,9 32 535 263.5 61 I 1,2,3,4,5,6,7,8,9,10

Table 7-1. Continued.

13#

Reflector No.

M*>':;#.05>'#:;*#0&>*#?OI#

N&6#N&)*=:&5>#?G*'I#

N&6#?G*'I# E*90*=:5)#=0.++ K&+&/0*#9)5O#+;5:+#

29 350 261 66 I 1,2,3,4,8,9,10 30 420 263 70 I 1,2,3,4,5,9,10 39 47 261 71 I 1,2,3,6,7,10 37 930 253 73.5 I 1,2,3,4,5,6,7,8,9,10 38 775 250.5 77.5 I 1,2,3,4,5,6,7,8,9,10 36 795 260 77.5 I 1,2,3,4,5,6,7,10 42 186 252 78 I 1,2,3,4,6,7,10 35 717 256 78 I 3,4,5,6,7,9,10 31 390 249 80.5 I 1,2,3,4,5,9,10 33 480 249 81 I 1,3,5,6,7,8,9,10 6 -20760 180 10 II 1,2,3,6,7

12 -3138 175 20 II 1,3,7,8 23 -1415 173 22 II 3,5,7,9,10 44 300 251 41 II 3,4,9 43 -32.5 255 53 II 6,7,8 40 46.5 245 55 II 1,6,7,8,10 26 85 261 73 II 1,2,3,9,10 27 137 260 77 II 1,2,3

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2S#

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1 -5300 155 16 I 1,2,3,4,5,6,7,9,10 2 -3620 167 23 I 1,2,3,7,8,9,10 5 -3368 152 18 I 1,2,3,4,5,6,7,8,9 9 -2865 148 15 I 1,2,5,6,7,8,10 3 -2694 170 17 I 1,2,3,5,7,8,9,10 4 -2395 170 24 I 1,2,3,4,5,6,7,8,9,10

22 -2165 155 21.5 I 1,2,3,4,7,8,10 10 -2155 160 20 I 1,2,4,5,6,7,8,9,10 6 -2155 170 20 I 1,2,3,5,6,7,8,9,10

11 -1750 173 21 I 1,2,3,4,5,7,8,9,10 13 -1595 163 19.5 I 1,2,3,4,5,6,8,10 12 -1572 165 16.5 I 1,2,3,5,6,8,10 8 -1442 176 30 I 1,2,3,4,6,9,10

15 -1221 159 23 I 1,3,4,5,6,7,8,10 19 -1090 146 18 I 1,2,3,4,5,6,7,8,9,10 18 -1090 159 22 I 1,2,3,4,7,8,9,10 14 -1050 170 18 I 1,3,4,5,6,7,8,9,10 16 -665 177 25.5 I 1,2,3,4,6,7,8,9,10 23 -395 155 23.5 I 3,4,5,6,7,8,9 21 -46 127 29 I 4,5,6,7,8,9 24 105 134.5 40.5 I 1,2,5,6,8,9 43 145 255 73 I 1,2,3,6,7,9,10 33 240 260 77 I 1,2,3,9,10 25 510 261 60 I 1,2,3,4,9,10 29 555 265 76 I 1,2,3,4,5,7,8,9,10 34 710 263 68 I 1,2,3,4,5,6,7,8,9 42 800 258 67 I 2,3,4,5,7,8,9,10 35 830 250 82 I 5,6,7,8,9,10 27 980 255 85 I 1,2,3,4,5,6,7,8,9 41 1120 249 81 I 1,2,3,4,7,9,10 28 1120 259 86 I 1,2,3,4,5,10 38 1370 256 78 I 1,2,3,4,6,7,8,9,10 39 1455 259 77 I 1,2,3,4,5,6,7,8,9,10 40 1600 258 77 I 1,2,3,4,5,6,7,8,9,10 30 1720 250.5 77.5 I 3,4,5,7,8,9


2$#

Reflector No.

M*>':;#.05>'#:;*#0&>*#?OI#

N&6#N&)*=:&5>#?G*'I#

N&6#?G*'I# E*90*=:5)#=0.++# K&+&/0*#9)5O#+;5:+#

7 -3073 151 18.5 II 1,2,3,5,6,10 17 -625 132 26 II 5,6,8,9,10 20 -313 157 23 II 1,2,4,6,7,8 44 80 261 71 II 1,6,10 26 330 260 82 II 1,2,3,4,9,10 32 352.5 250 81 II 2,7,9,10

"#$%&'! 4)4/# E*90*=:5)# *0*O*>:+# &>9*))*G# 9)5O# 0&>*# H@A3C# .00# +;5:# 65&>:+C# .00#5)&*>:.:&5>+C# .00# =0.++*+4#K&*8# 9)5O#@,@RC# /*058# :;*#;5)&b5>4#-;*#/0(*# 0&>*# &+# :;*#;<G)56;5>*#0&>*C#:;*#)*G#G5:+#.)*#:;*#+;5:#65&>:+C#.0+5#+;58>#&>#%&'()*+#2,1#.>G#2,1C#.>G#0&+:*G#&>#-./0*#2,34

21#

#

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22#

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23#

!!!"#$%&'! 4)*74#H@A# 34# E*90*=:5)# *0*O*>:+C# 058# G&6C#Q0.++# X4# K&*8# 9)5O# @,@cC# /*058# :;*#;5)&b5>4#-;*#/0(*#0&>*#&+#:;*#;<G)56;5>*#0&>*C#:;*#)*G#G5:+#.)*#:;*#+;5:#65&>:+C#.0+5#+;58>#&>#%&'()*#2,1#.>G#2,1C#.>G#0&+:*G#&>#-./0*#2,34

2T#

"#$%&'!4)**4#H@A#34#E*90*=:5)#*0*O*>:+C#058#G&6C#Q0.++#XX4#K&*8#9)5O#@,@cC#/*058#:;*#;5)&b5>4 -;*#/0(*#0&>*#&+#:;*#;<G)56;5>*#0&>*C#:;*#)*G#G5:+#.)*#:;*#+;5:#65&>:+C#.0+5#+;58>#&>#%&'()*+#2,1#.>G#2,1C#.>G#0&+:*G#&>#-./0*#2,34#

31#

3 CO+B"NE$ "NTE#)#ETAT"ON OF ALL *S) AN$ (S) $ATA

3,! ;8F$X$W8F$V&*-/KF',./*#$?#.*#9-,'$S/--/4A$ The azimuth estimates obtained by single-hole / single line analysis are improved by the concurrent processing of all profiles. To facilitate the consistent interpretation of the considerable number of reflection events, an attempt is made to lin2 the ones li2ely to represent the same feature in different profiles. However, this reduction procedure cannot easily be done interactively, as the gap between layouts Nboth between the boreholes, and the shot pointsO is often large and the site features are not necessarily planar. Solving the problem requires the use of statistical methods, e.g. clustering analysis. If the profiles are measured in the same borehole Nor along the same surface layoutO, the mean orientation of a reflector can be found in a stereographic representation NZulff diagramO at the intersection of the dip-azimuth curves computed for each profile, as shown in %&'()*# 3,1.. /ach dip-azimuth curve describes the possible orientations associated with the same time-depth function in a given profile. As fracture zones develop more or less along planes, their images in profiles measured with the same receiver layout are assumed to have the same intersection position along the layout and the stereographic proRection is computed at this specific position. The intersection, the dip and the azimuth determine completely the position and orientation of a reflector. The stereographic representation method is not applicable to profiles measured in different boreholes because the intersection positions vary widely due to lateral eYtrapolation. The 3D fitting procedure eYemplified in %&'()*#3,1#/#and %&'()*#3,2#is applied instead. /ach curve is the locus of a \CruY Point], defined as the foot of the perpendicular descended on a given reflection plane from an origin common for all profiles. The CruY Points from %&'()*# 3,2# have been computed for profiles measured in four different boreholes, the curves described by their loci being more compleY than the ones from %&'()*#3,1#/.

!

!

!

!

!

!

!

!

"#$%&'!5)*4#?.I#c(099#G&.').O4######## # # ?/I#Q)(B#65&>:#G&.').O4#

32#

%&'()*#3,2#displays also the segments of the reflecting interface actually covered by the four profiles. The results obtained are presented in Chapter 8.2 below.

"#$%&'! 5)(/# Q)(B# 65&>:# G&.').O# 95)# )*90*=:5)# 9&::&>'# .O5>'# K@A# 6)59&0*+# O*.+()*G# &>#G&99*)*>:#/5)*;50*+4##

4#1

4#2

4#!& 4#!!

3!#

3,& <4-#A'+-#0$8/-#$V,0#*$=+%#0$,4$-"#$;8F$Y$W8F$8#/%3/9$D+-+$#The interpretations of the site reflectors Npresented in Chapter 6 for each boreholeO are summarised in -./0*# 3,1 below. The reflector numbers are the same as in -./0*+# 1,1 through 1," and corresponding %&'()*+# 1,1 through 1,1T. The CruY Point for each reflector Na reflector origin, proRected to the plane defined by the reflectorO is defined as presented in Chapter 8.1 above. Of the 27 site reflectors, the nos. 3, 6 and 20 are not seen from boreholes KR11 and KR12, nos. 7, 9, 10, 19 and 24 from KR11, and no. 16 from KR12. Reflector 17 is not observed from KR7 and KR11. Reflectors 12 and 27 are only seen from KR7, and nos. 25 and 26 only from KR12. Others are observed from all 4 boreholes. #+,-.'!5)*/ K@A#)*90*=:5)+#&>:*)6)*:*G#9)5O#.00#K@A#/5)*;50*+4#

E*90*=:5)#G.:.# Q)(B#A5&>:#

E*90*=:5)#P54#

N*6:;#?OI#&>#

/5)*;50*#

N&6#N&)*=:&5>#?G*'I#

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Y5)*;50*P5):;&>'##?OI#

R.+:&>'#?OI#

R0*7.:&5>#?OI

1 694.6 200.0 20.0 I 6 92833.3 26045.0 -756.0

1 1008.7 200.0 20.0 III 7 92833.3 26045.0 -756.0

1 765.0 200.0 20.0 II 11 92833.3 26045.0 -756.0

1 856.5 200.0 20.0 II 12 92833.3 26045.0 -756.0

2 560.0 220.0 55.0 II 6 93089.0 26383.9 -464.0

2 1615.4 220.0 55.0 III 7 93089.0 26383.9 -464.0

2 635.0 220.0 55.0 I 11 93091.1 26385.6 -465.9

2 1180.1 220.0 55.0 III 12 93089.0 26383.9 -464.0

3 30.8 180.0 10.0 III 6 92591.8 25949.8 -104.9

3 200.2 180.0 10.0 I 7 92591.8 25949.8 -104.9

4 254.1 175.0 12.0 II 6 92639.3 25943.9 -310.6

4 424.3 175.0 12.0 II 7 92639.3 25943.9 -310.6

4 342.8 175.0 12.0 II 11 92639.3 25943.9 -310.6

4 345.0 175.0 12.0 II 12 92639.3 25943.9 -310.6

5 319.2 175.0 15.0 I 6 92678.0 25940.5 -389.5

5 532.7 175.0 15.0 II 7 92678.0 25940.5 -389.5

5 430.5 175.0 15.0 I 11 92678.0 25940.5 -389.5

5 440.0 175.0 15.0 I 12 92678.0 25940.5 -389.5

6 -1046.4 232.0 79.1 II 6 92282.6 25580.4 99.5

6 200.0 232.0 79.1 III 7 92282.6 25580.4 99.5

3"#


E*90*=:5)#G.:.# Q)(B#A5&>:#

E*90*=:5)#P54#

N*6:;#?OIN&6#

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R.+:&>'#?OI#

R0*7.:&5>#?OI

7 -52.2 250.0 75.0 III 6 92606.9 26046.5 -18.8

7 1220.9 250.0 75.0 I 7 92606.9 26046.5 -18.8

7 220.2 250.0 75.0 II 12 92606.9 26046.5 -18.8

8 537.8 226.0 52.5 I 6 92995.0 26388.1 -458.8

8 1490.1 226.0 52.5 II 7 92995.0 26388.1 -458.8

8 485.0 226.0 52.5 I 11 92995.0 26388.1 -458.8

8 1037.6 226.0 52.5 III 12 92995.0 26388.1 -458.8

9 565.0 260.0 70.0 I 6 92642.9 26353.4 -140.4

9 1634.6 260.0 70.0 II 7 92642.9 26353.4 -140.4

9 789.6 260.0 70.0 I 12 92642.9 26353.4 -140.4

10 500.1 255.0 70.0 I 6 92680.9 26357.5 -144.8

10 1652.4 255.0 70.0 II 7 92680.9 26357.5 -144.8

10 816.0 255.0 70.0 I 12 92680.9 26357.5 -144.8

11 391.9 160.0 25.0 I 6 92785.7 25871.9 -479.5

11 705.0 160.0 25.0 I 7 92785.7 25871.9 -479.5

11 635.2 160.0 25.0 II 11 92785.7 25871.9 -479.5

11 627.9 160.0 25.0 II 12 92785.7 25871.9 -479.5

12 350.0 240.0 60.0 III 7 92470.4 25774.3 125.8

13 417.2 225.0 62.0 I 6 92985.7 26363.8 -302.5

13 1625.0 225.0 62.0 I 7 92985.7 26363.8 -302.5

13 270.0 225.0 62.0 II 11 92985.7 26363.8 -302.5

13 1070.7 225.0 62.0 II 12 92985.7 26363.8 -302.5

14 830.0 175.0 20.0 I 6 92885.8 25922.3 -857.4

14 1090.8 175.0 20.0 I 7 92885.8 25922.3 -857.4

14 950.0 175.0 20.0 III 11 92883.1 25922.6 -850.0

14 1005.5 175.0 20.0 II 12 92885.8 25922.3 -857.4

15 638.0 224.2 65.4 I 6 93130.9 26494.1 -349.3

15 2023.7 224.2 65.4 II 7 93130.9 26494.1 -349.3

15 748.8 224.2 65.4 I 11 93130.9 26494.1 -349.3

15 1503.7 224.2 65.4 I 12 93130.9 26494.1 -349.3

16 418.3 177.5 20.0 I 6 92759.8 25941.6 -508.4

16 715.0 177.5 20.0 I 7 92759.8 25941.6 -508.4

16 561.3 177.5 20.0 II 11 92759.8 25941.6 -508.4

3$#


E*90*=:5)#G.:.# Q)(B#A5&>:#

E*90*=:5)#P54#

N*6:;#?OIN&6#

N&)*=:&5>#?G*'I#

N&6#?G*'IE*90*=:5)#Q0.++#

Y5)*;50*P5):;&>'##?OI#

R.+:&>'#?OI#

R0*7.:&5>#?OI

17 183.9 225.0 57.0 II 6 92835.8 26213.9 -233.8

17 650.0 225.0 57.0 I 12 92835.8 26213.9 -233.8

18 167.5 169.9 8.0 II 6 92600.9 25944.6 -202.3

18 276.0 169.9 8.0 I 7 92600.9 25944.6 -202.3

18 235.2 169.9 8.0 I 11 92600.9 25944.6 -202.3

18 223.2 169.9 8.0 III 12 92600.9 25944.6 -202.3

19 -647.2 252.4 82.3 II 6 92498.1 25718.2 41.7

19 680.1 252.4 82.3 II 7 92498.1 25718.2 41.7

19 -685.3 252.4 82.3 III 12 92498.1 25718.2 41.7

20 -410.0 247.2 71.6 III 6 92520.9 25828.7 52.4

20 662.1 247.2 71.6 I 7 92520.9 25828.7 52.4

21 978.3 245.0 53.5 II 6 92917.8 26692.0 -597.2

21 1852.4 245.0 53.5 III 7 92917.8 26692.0 -597.2

21 959.9 245.0 53.5 I 11 92917.8 26692.0 -597.2

21 1347.0 245.0 53.5 III 12 92917.8 26692.0 -597.2

22 861.5 225.0 55.0 II 6 93197.8 26575.9 -611.2

22 1939.8 225.0 55.0 I 7 93197.8 26575.9 -611.2

22 1070.1 225.0 55.0 I 11 93197.8 26575.9 -611.2

22 1525.8 225.0 55.0 II 12 93197.8 26575.9 -611.2

23 1562.4 260.9 67.0 II 6 92735.4 26971.9 -430.0

23 2709.9 260.9 67.0 II 7 92735.4 26971.9 -430.0

23 3170.0 263.0 67.5 II 11 92691.3 26923.4 -397.5

23 1898.1 260.9 67.0 II 12 92735.4 26971.9 -430.0

24 110.2 255.0 78.0 I 6 92615.0 26111.5 -26.8

24 1500.5 255.0 78.0 I 7 92615.0 26111.5 -26.8

24 398.1 255.0 78.0 II 12 92615.0 26111.5 -26.8

25 700.0 180.0 5.0 II 12 92571.7 25949.8 -671.6

26 780.0 180.0 0.0 I 12 92571.7 25949.8 -748.9

27 875.0 175.0 30.0 II 7 92881.4 25922.7 -529.7

31#

"#$%&'!5)0/#Q5O/&>*G#&>:*)6)*:.:&5>#59#.00#K@A#.>G#H@A#G.:.4#K&*8#9)5O#@,@cC#/*058#:;*# ;5)&b5>4# Y5)*;50*+# .)*# &>G&=.:*G#8&:;# /0(*# 0&>*+C# .>G# +;5:# 65&>:+#8&:;# /0(*# ?DE2IC#6&>F#?DE1IC#')**>#?DE11I#.>G#)*G#?DE12#.>G#H@AI#G5:+C#)*+6*=:&7*0<4#

32#

7 CONCL%S"ONS

The quality of data measured in OL-KR6, OL-KR7, OL-KR11 and OL-KR12 was very good and in many cases the same reflectors have been interpreted in all surveys. The HSP data has been of a more modest quality, mostly due to the higher cultural noise and to the absorbing effect of the soft deposits at the bottom of the pond, and possibly more fractured near-surface roc2 mass. However, after processing the HSP data displays the same reflector orientations as the VSP data and a cohesive model can be constructed. Based on ample direct and indirect verifications of results, the multi-azimuth, multi-offset VSP can be considered an effective method for mapping fracture zones in hard roc2. The new VIBSIST source produces signals with levels of energy comparable to eYplosives. The VIBSIST appears to be more stable, but its most significant advantages are the low cost of preparation of the shot points and the speed of the acquisition. A topic that demanded a level of effort higher than eYpected was the elimination of disturbing multiples NringingO from the records. The correlation procedure has been improved and the multiples were finally eliminated. Depending on the direction of incidence of the incoming wave and the reflecting boundary, PP and/or PS reflections can be generated. Ambiguities may appear e.g. due to the erroneous interpretation of PS reflected conversions as PP reflections. The result is that the reflector may be interpreted as having a different dip than its real one. The strategy used for avoiding such errors has been based on a \voting scheme] applied to trial fits with both PP and PS time functions. The interpretations that fitted most consistently amongst all the profiles were retained. Fenuine PP reflectors seem to have been identified in all cases. The increase of the number of shot points to ten per survey, made possible by the use of the VIBSIST 1000 source, has definitely paid bac2 in terms of improved coverage and decrease of uncertainty related to the interpretation of the reflectors. The same reflectors could now be unambiguously identified in a sufficient number of profiles to ma2e them certain. Moreover, the increased precision in orientation resulting from the larger number of offsets and azimuths allowed the interpretation to be transported from one survey to another, the combined model being much more cohesive than with earlier surveys. A further increase of the resolution and reliability of the results may involve clusters of shots disposed as cross-shaped arrays with transverse directions of the order of one wavelength, i.e. app. 30 m, at 5 m intervals. These arrays would have a stronger directional filtering effect on steeply inclined reflectors than on the sub-horizontal ones, as the wave front reflected on the latter would be nearly synchronous for all the shots in the array. This is eYactly where the added information would mostly be needed.

3T#

#898:8;<8= Bednar, e.B. and Zatt, T.L., 1984. Alpha-trimmed means and their relationship to the median filters, I/// Transactions on Acoustics, Speech and Signal Processing, vol. ASSP-32, no. 1, pp. 145-153. Cosma, C. 1990. Seismic Imaging Techniques Applied to Roc2 /ngineering. Invited paper. Proceedings of The 1st S/Fe International Symposium on Feotomography, To2yo, eapan. Cosma, C., Hei22inen, P.e. and Kes2inen, e., 1994a. Development of seismic investigation techniques, Part IV Coverage analysis of VSP surveys. TVO, Helsin2i. Zor2 report PATH-94-02e. Cosma, C., Hei22inen, P.e. and Kes2inen, e., 1994b. Development of seismic investigation techniques, Part IIV Site coverage of VSP surveys in Romuvaara, borehole KR2. TVO, Helsin2i. Zor2 report PATH -94-03e. Cosma, C., 1995. Characterisation of subsurface structures by remote sensing. Keynote address. Proceedings of the 1st International Congress on Roc2 Mechanics NISRMO, To2yo, eapan. Cosma, C. and Hei22inen, P. 1996. Seismic Investigations for the Final Disposal of Spent Nuclear Fuel in Finland. eournal of Applied Feophysics vol. 35, pp. 151–157. Cosma, C., Hei22inen, P.e., Kes2inen, e. and /nescu, N., 2001a. VSP in Crystalline Roc2s – from Downhole Velocity Profiling to 3-D Fracture Mapping. International eournal of Roc2 Mechanics and Mining Sciences, vol. 38, no. 6, pp. 843 - 850. Cosma, C., Olsson, O., Kes2inen, e. and Hei22inen, P.e., 2001b. Seismic characterisation of fracturing at the hspg Hard Roc2 Laboratory, from the 2ilometre scale to the meter scale. International eournal of Roc2 Mechanics and Mining Sciences, vol. 38, 6, pp. 859 -865. Cosma, C. and /nescu, N., 2001c. Characterization of Fractured Roc2 in the Vicinity of Tunnels by the Swept Impact Seismic Technique. International eournal of Roc2 Mechanics and Mining Sciences, vol. 38, no. 6, pp. 815 – 821. Cosma, C., /nescu, N. and Kes2inen, e. 2002a. Vertical Seismic Profiling from KLl-02, LaYemar, 2000. SKB Technical Document, TD-02-02. Cosma, C. and /nescu, N., 2002b. Multi-Azimuth VSP Methods for Fractured Roc2 Characterization, the 5th ISRM Conference, Toronto. /nescu, N. and Cosma, C., 1999. VSP Investigations for the Malmg City Tunnel proRect.Zor2 report, DFI, Denmar2.

TS#

Hei22inen, P.e. and Cosma, C., 1994. Development of seismic investigation techniques. Part IIIV Fast 3D-modeling of VSP surveys. TVO site investigations, Zor2 report PATH-94-04e. Hei22inen, P.e., Cosma, C. and Kes2inen, e., 1995. Development of Seismic Investigation TechniquesV Anisotropy in VSP Measurements. Zor2 Report PATH-95-58e. euhlin, C., Bergman B., Cosma C., Kes2inen e. and /nescu N. 2002. Vertical Seismic Profiling and Integration with Reflection Seismic Studies at LaYemar, 2000. SKB Technical Report, TR-02-04. Kes2inen, e., Cosma, C. and /nescu, N., 1999. Seismic Investigations at the Fletchel Mine, Zinnemucca, Nevada. Zor2 report, PlacerDome, HSA. Kes2inen, e., Cosma, C. and /nescu, N., 2000. VSP Structural Survey at the Onaping Depths in Sudbury4#Zor2 report, Falconbridge Limited, Canada. Par2, C.B., Miller, R.D., Steeples, D.Z. and Blac2, R.A. 1996. Swept Impact Seismic Technique NSISTO. Feophysics, vol. 61, no. 6, pp.1789 – 1803.

T1#

A))EN$"CES AppendiY A. Image Space Transform page 93 AppendiY B. IP Migration and the 3-D CDP Transform page 95 AppendiY C. Data plots from HSP7V High & Low dip IP Migration page 97 AppendiY D. Data plots from HSP8V High & Low dip IP Migration page 107

T!#

A))EN$"> A, "?@A8 SB@<8 T:@;=9C:?

The reflecting interfaces in the roc2 mass are generally from lithological contacts but can also be from faults, fracture zones and dissolution features. Those reflections from faults and fracture zones usually display relatively wea2 seismic characters and eYtensive processing is needed to obtain information on the position of the reflectors from the seismic profiles. It is necessary to improve the signal-to-noise ratio, so that the later events Ne.g. reflectionsO become visible. As the reflection coefficients are eYpected to be low, the reflectors cannot usually be identified by amplitude contrast. Phase consistency is a more sensitive indicator. The Image Point transform is a technique developed for both filtering and interpretation of VSP profiles. Li2e the &,6#method, it is based on the Radon-transform, but while in the &,6#transform the traces are stac2ed along straight paths across the section, in the Image Point transform the stac2ing is done along paths lining up with travel times corresponding to possible real reflectors. This gives to the Image Point transform two advantagesV the signal coherence can be used as effectively as possible to enhance the wea2 reflections and the transformed section in Image Point Space can be directly used as an interpretation tool, to estimate the strength and position of the reflectors. The approach permits the determination of both the 3-D position and local orientation of the observed reflectors. The physical meaning of the procedure is that each reflection event can be considered as being produced by an iimage sourcej from which the signal propagate to each receiver on a direct path, much li2e the mirror effect in optics. The mirror on which the image source is formed is a reflecting roc2 feature, e.g. a fracture zone, as shown in %&'()*#],1. The Image Point transform of a depth-time profile gNz,tO is obtained by stac2ing along paths, all possible values of ' and (, i.e. to all possible orientations of the reflecting planes. The direct transform is eYpressed asV

bIIGb4gC?:\:'?bC\IC? )

b

b

('(' )*maY

min

The function trN',(kzO gives the travel times corresponding to the planar reflector specified by ( and ' , to the detector at the depth zV h=2b,ba\: 22

) '( where +'( 22a\

T"#

"#$%&'!8)*4# #@=;*O.:&=#6)*+*>:.:&5>#59#:;*#XO.'*#A5&>:#-).>+95)O4##

The inverse transform has the following eYpressionV

''((''

'

IIGg:C?b\C?HG:G\I:C'?b ) ,,*,

,, )2

1

where '( 2bab,:=\ 222

) The derivation and the Hilbert transform H restore the original signal shape. In the Image Point transform, coherent reflection events collapse to points. Therefore, the signal coherence can be used as effectively as possible to enhance the wea2 reflections. Zithin a certain range for the propagation velocity c, only real reflectors produce coherent patterns along their integration paths. Therefore, the inverse transform from the Image Point space to the depth-time space always leads to a filtered version of the reflection profile. Zith the Image Point method, two of the three parameters defining the 3-D position of a reflector can be determined. The reflectors with image points located on a circle perpendicular to the borehole generate equal travel times to all detectors. In order to determine uniquely the 3D position and orientation of a reflector, means should be found to estimate the dip direction. An effective method is to use polarisation analysis. The reflected signals do not stac2 constructively along the image point integration path if the reflector is not a plane. This problem is solved by dividing the time-depth section into several overlapping panels, each containing a subset of the traces. For each panel, the Image Point transform is computed independently.

T$#

A))EN$"> B, ") +"'#AT"ON AN$ T(E -.$ C$) T#ANSFO#+ By comparison, to 2-D and 3-D seismic, the offset vertical seismic profiles NOVSPO are more difficult to interpret because they are not usually displayed as a zero-offset sections or volumes. The approach followed so far has been to compute reflector positions and orientations from the travel time functions in depth-time representations and to display them in 3-D as reflection elements. A possible difficulty that this approach may run into is that the decision on what is a true reflector and what it isn]t is made before the 3-D display and the interpretive advantage of the perspective view is thus lost. The IP migration attempts to compute 3-D coordinates of the reflection points corresponding to a class of reflectors defined e.g. by the same stri2e and dip. The main difference between the IP migration and the VSP-CDP transform eYplained by NZyatt and Zyatt, 1984O lays in the fact that with the IP migration the reflection points are computed directly in 3-D, by firstly constructing a 1-dimensional variety to represent the locus of a class of image sources. The locus of the reflection points associated with the set of images and the linear array of detectors forms a 2-dimensional variety, which may, but does not necessarily, follow a plane. If a proRection plane is chosen, it can in particular be the one containing the CDP Ncommon depth pointsO, in which case the proRection of the IP migration becomes identical with the VSP-CDP transform. The CDP Transform has been eYtensively used in petroleum eYploration as one of the few imaging methods for OVSP data sets NFras and Craven, 1998O. Similar applications in the hardroc2 environment are rare. One eYample is the imaging of steeply dipping volcanic stratigraphy in the vicinity of the Kidd Cree2 deposit in North – /astern Ontario by N/aton et al., 1996O. Hnli2e with the VSP-CDP transform, with the IP migration the traRectory reconstruction is done directly in 3-D and a constant velocity is not required, the travel time functions being computable, in principle, for any velocity model. Another serious limitation with CDP, namely that the transform does not handle properly data corresponding to other dips and stri2es than the value assumed, is elegantly solved by the IP migration, because other orientations than the ones permitted are suppressed by IP filtering. The same applies to diffractors. Li2e the general IP transform, the IP Migration is essentially 2-Dimensional and the 3-D geometry of the reflectors cannot be resolved with data from a single profile. The maRor utility of IP migration lies in the possibility that it opens for interpreting reflectors of a lesser character, belonging to the same orientation classes as a maRor event used to define the respective class. #898:8;<8=

/aton et al., 1996. Seismic Imaging of massive sulfide deposits, Part III, Borehole seismic imaging of near-vertical structures, /conomic Feology, Vol 91, p.835-840

Zyatt, K.D., and Zyatt, S.B. 1984. Determining subsurface structure using the vertical seismic profile. X> Vertical Seismic Profiling, Part BV Advanced Concepts, *G&:*G#/< M.N. To2soz and R. Stewart. Feophysical Press, London, 419 p.

T1#

Fras, R. and Craven, M. /., 1998, Interpreterus Corner - Integrated wor2station interpretation of multi-azimuth offset VSP data - west TeYas case studyV The Leading /dge, 17, no. 03, 306-310.

T2#

A))EN$"> C, $ATA )LOTS F#O+ (S)2D ("'( 6 LOE $") ") +"'#AT"ON

1S2#

A))EN$"> $, $ATA )LOTS F#O+ (S)3D ("'( 6 LOE $") ") +"'#AT"ON

LIST OF R/PORTS 1 N1O POSIVA-reports 2003, situation 4#2003 POSIVA 2003-01 Vertical and horizontal seismic profiling investigations at Ol2iluoto,

2001 Q.0&>#Q5+O.C#P&=50*:.#R>*+=(C#R)&=F#]G.OC#M(=&.>#Y.0(

Vibrometric Oy March 2003 ISBN 951-652-115-0

ISBN 951 -652 -115 -0ISSN 1239 -3096

vertical and horizontal seismic profiling investigations at olkiluoto

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