well-site biostratigraphy of danish horizontal

Geological Society, London, Special Publications

doi: 10.1144/GSL.SP.1999.152.01.05p75-84.

1999, v.152;Geological Society, London, Special Publications D. J. Shipp Well-site biostratigraphy of Danish horizontal wells

serviceEmail alerting

new articles cite this article to receive free e-mail alerts whenhereclick

requestPermission

part of this article to seek permission to re-use all orhereclick

Subscribe

Collection London, Special Publications or the Lyell

to subscribe to Geological Society,hereclick

Notes

© The Geological Society of London 2012

at Simon Fraser University on April 20, 2012http://sp.lyellcollection.org/Downloaded from

http://www.lyellcollection.org/cgi/alerts

http://www.geolsoc.org.uk/gsl/publications/page417.html

http://sp.lyellcollection.org//site/subscriptions/

http://sp.lyellcollection.org/

Well-site biostratigraphy of Danish horizontal wells

D. J. S H I P P

Robertson Research International Limited, Llanrhos, Llandudno, Gwynedd LL30 1SA, UK

Abstract: The number of horizontal and subhorizontal wells drilled has significantly increased over the last decade, especially during the last five years, and the use of horizontal wells in oil-field production and development is now routine. In 1987 Maersk Olie and Gas AS drilled the first horizontal well on the Dan Field. Since that time biostratigraphers at Robertson Research International Limited have been involved in Maersk's pioneering work on the development of steering techniques for horizontal wells in the Danish sector of the North Sea. Well-site biostratigraphy has been successfully used to aid in the steering of these horizontal wells.

The background studies leading to the erection of highly detailed local biozonal schemes capable of detecting changes over vertical distances as little as 1 foot are described. The logistics of how well-site biostratigraphy is carried out at the well site is explained. In addition to Dan, well-site biostratigraphy has been successfully applied to development wells from several other Danish North Sea carbonate fields operated by Maersk Olie og Gas AS on behalf of the Danish Underground Consortium (a joint venture between Shell, Texaco and AP Moiler). These fields include Harald, Kraka, Gorm, Roar, Skjold, Svend, Tyra and Valdemar. Over 100 wells from Danish fields have to date been effectively steered using high-resolution biostratigraphy. Vertical targets of 10-20 feet or less have been successfully followed over distances of several thousand feet.

The author and his colleagues have been fortunate to have been associated with the Danish-based company Maersk Olie og Gas AS which has drilled over 100 horizontal wells to date, and has been in the forefront of the application of this new technology in the North Sea. As a result of this association it has been possible to develop the required techniques for well-site biostratigraphy to assist in the steering of the horizontal wells.

Geological setting

The Danish sector of the North Sea contains a number of carbonate fields (Fig. 1). Most of these, namely Dan, Gorm, Harald East, Kraka, Roar, Skjold, Svend and Tyra, have reservoirs in Danian or Maastrichtian chalks (Anderson & Doyle 1990). The exception is the large Valdemar Field where the reservoir occurs in Aptian and Barremian limestones or marls of the Sola and Tuxen Formations (Ineson 1993) (Figs 2 and 3).

Origin of horizontal well-site biostratigraphy in Denmark

The use of biostratigraphy as a tool to aid in the geosteering of horizontal wells in Denmark was developed by Maersk Olie og Gas AS on the Dan Field (Fig. 4) where the target is within the upper Maastrichtian. On the early Dan Field horizontal development wells, well-site biostratigraphy was originally used only to identify the top of the Maastrichtian. It was quickly realized, however, that without well-site biostratigraphy it was possible to re-enter the Danian, which overlies the reservoir, while drilling the horizontal part of the well. A need for well-site biostratigraphy to monitor the drilling of the horizontal section was thus identified.

This was first undertaken on MFA-13 where the end of the build-section is stratigraphically the deepest part of the well. Biostratigraphic events identified on the build-section could then be recognized again as the horizontal section moved slowly back up stratigraphy due to the gentle dip of the beds away from the centre of

SHIPP, D. J. 1999. Well-site biostratigraphy of Danish horizontal wells. In." JONES, R. W. & SIMMONS, M. D. (eds) Biostratigraphy in Production and Development Geology. Geological Society, London, Special Publications, 152, 75-84.



76 D . J . SHIPP

H" ............. =. 4

...................................................... l ' °0 ' " 0 ' '. I ~ s o 3 i I i l sso4 ~os ' ~ [ [ i 1 IVALD~MAR i

o ... . . . . . . . . . . . . . . . . . . . . . . , ,

Tyra ............ 19 Harald E .....,1 N _ _ "'4R~ IGOR G .............. 16 R ................ 2 ( 3 GORM

Kraka .......... 6 "-~DAGMA SKJOLD~ 1.... ('~ ALMA Valdemar ....4

Skjold .......... 11

Numbers indicate horizontal wells which have been monitored using wellsite biostratigraphy up to end 1996

' i T

'< ~\ l ' " ' ~ . _ i _ . J ;

t~ ¸

/ "+" \ ~ i, " ' \ .

A

1 k

I

,/i'

i ' i

i\ , i " . i ! \..~

iX.,

l l

!

Fig. 1. Location map showing position of Danish Central Graben relative to North Sea and (inset) position of Dansk Undergrounds Consortium Danish Fields together with a list of horizontal wells monitored by biostratigraphy on each field up to the end of 1996 (modified from Shipp & Marshall 1994).

the field (Fig. 5). The crude biostratigraphic zonation of MK1A and MK1B was established while drilling MFA-13 and, although poor, the four data points noted on Fig. 6 were sufficient to monitor progress towards the base of the Danian and permit adjustments to be made to the well path to stay within the Maastrichtian.

H i g h - r e s o l u t i o n b i o s t r a t i g r a p h y

In order to develop a zonal scheme with the degree of refinement required to aid in the steering of a horizontal well, a re-thinking of the way

zonations are established was required. Tradi- tionally donations for the Upper Cretaceous were based on ditch cuttings analyses from routine exploration wells, where a distance of 30 feet between samples was the rule. Thus, the uppermost Maastrichtian zone on the existing zonation scheme was 50-60 feet thick (MK1 on Fig. 6).

Traditional zonal schemes based mainly on first and last downhole appearances, and relying primarily on evolutionary changes, do not provide sufficiently close-spaced data for biosteering. A new method that provided a greater number of recognizable events over a given vertical distance was required. Thus, high-resolution



BIOSTEERING DANISH HORIZONTAL WELLS 77

" o

i-i-1

8 . < m

Z I"I'1

c "o "o r'rl

i-1-1

~>- O

5 m p o

-o --o c,q m

AGE

DANIAN

MAASTRICHTIAN

APTIAN AND BARREMIAN

LITHOSTRAT- FIELDS

IGRAPHIC UNITS

DAN, GORM, TYRA, KRAKA, SKJOLD,

HARALD SVEND ROAR

go o F

3> --aZ C~

EKOFISK FORMATION

TOR FORMATION

¢ ' )

xJ SOLA AND TUXEN VALDEMAR © © ~ FORMATIONS ;x:~ r n O N C ~ --e z

O i - - i - -

L I T H O L O G Y

I I I I I

I i i i i I I I

I I I I I

i i

I I I I I

I I I I I

, - t . - - - w ~ . .._.,..,.~ ~ _ _ • - ~ , - - . . -o . - ~ l

* i o * ; i ~ , i%-II°li

Fig. 2. Simplified stratigraphy for the Danish Central Graben carbonate fields showing age, lithostratigraphic units and lithology for the various fields (modified from Fine et al. 1992).

BARREMIAN FRACTURED DOMAL INTRA LIMESTONE CHALK CHALK CHALK

~ ~ Shale Upper Cretaceous

--"~rll~i--ll---ll.4[ll.._,~ _ ]" . I'~----t--7-t--~S~_ ,,~ " i . ._ " ~ - & : : 3 E Z T _ . p ~ ~ Chalk

. . . . "" " e l " Upper Jurassic W ' ' i ' " '::~! ~ " : ~ ~

7 +.+.+,-,+,+_ " . ~ . - . . • RINGKOBING-FYN

. ~ ~ I4- + + +~-+~+~ - - - ~ ~ ~ /%+ :+++++++++++: .+++++++++++ \ +++++++++++

,,

" C ~. ." -2" L \ . - , # -- "-,1--',,:

Fig. 3. Schematic E-W section through the Danish Central Graben showing geological setting and trap types of carbonate fields discussed (modified from Anderson & Doyle 1990).



78 D . J . SHIPP

Fig. 4. Contour map of the Dan Field showing horizontal wells drilled up to January 1992. Note wells MFA-13 and MFA-18. Contours are top Maastrichtian, Tor Formation (after Fine et al. 1992).

biostratigraphy was developed where counts are made of all the fossils recorded to establish a refined local event stratigraphy. A high-resolution approach reveals changes in the overall composition of the microfossil assemblages which can produce much more refined zonations than presence or absence criteria and total ranges. The zonal schemes are based on local assemblage, partial range and acme biozones, and principally reflect changes in the environ- ment rather than evolution. It might be thought that relying on environmental changes could cause problems with diachronous events. Within

the confines of a single field, however, this generally presents no problem, and events can be readily correlated across the field while some can also be correlated between fields.

The first stage in the development of a zonal scheme for a particular field is the analysis of samples from offset wells. These are normally straight holes. Cores and sidewall cores provide the best database as ditch cuttings are often contaminated with cavings. Sample spacing is ideally at 10-5 feet across the target horizon, but studies on samples as close as 1 foot have been undertaken.




• . i..~: ii i~ ~. ! :i~.~: !)i~. ~. ! :i~i-i: iii"..:. ! :i~i-i: i-i ii. ! :i~i.-~: !.i i~ ~. !:iii. i ~ ii i"/. !:iii . i: ii i"/. ! :i~i.-~ I iii"-/. ! :i".i. i I i-i i"/. ! :i".i. i: i-i i~ ~. ! (".i.~ I i-i i~ :. ! :i".i-~ii.i " :". :. ! :i~i.~: !-i i~/. ! :i~i '

i;i!ii!i : !i i i: ii!il ii !i:!i iil;ill - ~ . . . . . . . . . . . . or horizo, ntal section

- *

Fig. 5. Diagram of a horizontal well showing the pilot hole, build-section and horizontal or drainhole section. Structure of target horizon is as the Tor Formation on the Dan Field where the end of the build-section is stratigraphically the oldest part of the horizontal well.

A pilot study may include analyses for both micropalaeontology (foraminifera, ostracods, radiolaria and macrofossil debris) and nannofossils (coccoliths and nannoconids). In general, Maastr icht ian targets can be adequately zoned by micropalaeontology while in the Danian a combinat ion of both micropalaeontology and nannofossils proves most useful. This is also true of the Lower Cretaceous. A simplified version of a typical biostratigraphic chart showing both nannofossil and micropalaeontological zones is shown in Fig. 7.

Analyses are usually carried out in the labora- tory, and a prel iminary zonal scheme erected before undertaking any work at the well site. It is possible, however, to erect a zonal scheme on

samples from a pilot hole drilled prior to the horizontal well. This was the case on the first horizontal well on the Danian Kraka Field where a prel iminary zonal scheme was initially established from core pieces collected from the pilot hole and immediately used when the horizontal section was drilled a few days later. It should be noted that microfossil recovery from horizontal well ditch cuttings samples is generally very good with little contaminat ion by cavings. Consequently, zonal schemes can be significantly improved at the well site especially as a 30-foot spacing between samples may only represent a difference of 1 foot in a vertical sense.

As a result of further work on the Dan Field, in- cluding the monitoring of close to 50 horizontal



STA

ND

AR

D

UP

PE

R

CR

ETA

CE

OU

S

ZON

E

MK

1

TEN

TATI

VE

ZO

NE

S

DA

N F

IELD

MK

IA

MK

IB

PO

TEN

TIA

L C

OR

RE

LATI

VE

E

VE

NTS

"~"1

P

seud

otex

tufa

ria

spp.

•

~---

-q

Cal

care

ous

bent

honi

c fo

ram

s.

Cal

care

ous

bent

honi

c fo

ram

s. O

?1

Ru~

locJ

Iobi

[lerin

a sp

p.O

OR

IGIN

AL

DA

N Z

ON

AT

ION

BA

SE

D O

N M

FA

-13

(UP

PE

R P

AR

T)

ii I

/ /

/

ZON

ES

DM

1

C.5

0'

kk

I D

M2C

DM

3

\ \ \

\ D

M4

PRIN

CIP

AL E

VE

NTS

LE

GEN

D I

Com

mon

Si

ngle

eve

nt

~ "lo

p O

Rar

e •

Abun

dant

To

tal r

ange

~

Base

•

Occ

asio

nal

••

Supe

rabu

ndan

t ...

..

" "~

-'q

P.

bra

zoen

sis/

acer

vulin

oide

sOfl

> P.

e/e

gans

•t~

, R

. fru

ctic

osa

G. c

lem

entia

na s

ubsp

. (?

loca

l)

~_

~

Pla

nogl

obul

ina

spp.

II,

P. el

egan

s> P

. bra

zoen

sis/

acer

vulin

oide

s R

. con

tusa

O,

P. la

evis

O,

B. d

raco

dra

co,

Pra

ebul

irni

na l

aevi

s H

. glo

bulo

sa O

, G. a

sper

0,

S. b

ecca

riifo

rmis

D

M2A

,~

--J

G. c

lem

entia

na s

ubsp

. (?

loca

l)

Pla

nogl

obul

ina

spp.

e/!

Cal

cisp

here

s I,

__

~j

P.e

lega

ns e

lega

ns I

/m,

R,

fruc

ticos

a "~

--

G, v

oltz

iana

(Ioc

al)

I R

.con

tusa

I,

S.p

omm

eran

a: G

lobo

trun

cana

arc

a ~ )

/0,

~-

C.

vela

scoe

nsis

•,

R. r

ugos

a ~:

)/0, O

. vat

iabi

lis,

)/0,

D

M2B

I

G. b

embi

x, I

noce

ram

us

(loca

l) ~-

?~F

~---

q C

alci

sphe

res

(loca

l) rn

crea

se H

. gl

obul

osa,

G. a

sper

, B.

mul

tispi

na,

Pith

onel

la s

p.,

S. p

omm

eran

a 0,

B.

drac

o cl

raco

•

~R

In

flux

radi

olar

ia (

Cen

osph

aera

spp

./C

enod

/scu

s sp

p., g

lass

y),

loca

l • r

ugos

a O

/Q,

Pith

onel

la 0

, Sp

icul

e X

~-_-

--I

R. c

ontu

sa B

, P.

e/e

gans

O,

S. p

omm

eran

a O

, P.

laev

is •

I G

. arc

a {-

.)/•,

R.c

ontu

sa,

Cen

osph

aera

spp

. (ch

alky

, loc

al)

Bryo

zoa,

Ino

cera

mus

(lo

cal)

R. r

ugos

a II,

incr

ease

agg

lutin

ated

for

amin

ifera

PR

ES

EN

T D

AN

ZO

NA

TIO

N

(UPP

ER

PA

RT

)

Fig.

6.

Dan

Fie

ld m

icro

pala

eont

olog

ical

zon

al s

chem

es s

hovi

ng (

left

) th

e ea

rly

sche

me

base

d on

MF

A-1

3 to

geth

er w

ith

stan

dard

Upp

er C

reta

ceou

s zo

ne a

t th

at t

ime

and

(rig

ht)

the

pres

ent-

day

sche

me

for

the

equi

vale

nt s

ecti

on (

repr

oduc

ed w

ith

perm

issi

on f

rom

Mae

rsk

Oli

e og

Gas

AS)

.

at S

imon

Fra

ser

Uni

vers

ity o

n A

pril

20, 2

012

http

://sp

.lyel

lcol

lect

ion.

org/

Dow

nloa

ded

from



I-!.l M5B I M5A I N3A

M2 I M1 N2-N1 I

I i i ] \ - 4 ' ' '

/

v

I

MICRO-FOSSIL NANNO-FOSSIL Depth Scale 1 : 500 (feet)

Abundance Scale l cm = 2 5 %

Anornalinoides velascoensis Anomalinoides hyphalus Anomalinoides/Gavelinella spp. Cibicides/Heterolepa spp.

Gavelinella beccariiformis

Gyroidinoides subangulata Lenticulina spp.

Nodosariidae Osangularia lens Polymorphindae Quadrimorphina halli Cibicides succedens Pullenia amercana

Dentalina/Nodosaria spp.

Gavelinella bembix

Gyroidinoides nitida

Gyroidinoides quadrata

Lagena spp.

Osangularia cordierana

Pleurostomella spp.

Praebulimina laevis. Gavelinella cornplanata

Anomalinoides spp.

Anomalinoides welleri

Ramulina spp.

Fig. 7. Simplified biostratigraphic chart from the upper part of the Maastrichtian of Gorm Field. Micropalaeontological and nannofossils zones are shown on the left of the chart, while occurrences and abundances of foraminifera are shown to the right. A similar chart would also be produced for the nannofossils (after Shipp & Marshall 1994).

wells, the present-day Dan zonation (as shown in Fig. 6) with a significantly increased number of micropalaeontological data points has been developed. Individual zones are approximately 10 feet thick and can often be subdivided. Approximately 20 data points are now recognized in place of the four used on MFA-13 and the original single uppermost Maastrichtian zone of the traditional zonal scheme (Fig. 6). As a result of such developments it soon proved possible to monitor wells through the Maas- trichtian target zone over a distance of some

6000 feet (Fig. 8). The more recent MFB-2E well, drilled in 1996, was monitored over a horizontal distance of 11 420 feet, at the time a North Sea record.

Even greater refinement has been achieved over part of the Valdemar section, as shown in Fig. 9 which represents part of the zonation covering a 50-foot vertical section. A pilot study to establish the zonation was originally carried out on samples at 5-foot spacings through a core from a nearby well. This resulted in the micropalaeontology and nannofossil zones shown as



82 D . J . SHIPP

rrl

-r

Z

rm

m

+ooI

I000 l

J !i!i!!:

1500 i

l i e •

2000 : i J i

0 500 1000 1500 2000 2500 3000 3500 4000m

VERTICAL SECTION

Fig. 8. Dan MFA-I 8 well showing the trajectory of a horizontal section maintained within the target zone (after Shipp & Marshall 1994).

M zones and N zones. During the drilling of the Valdemar-2 horizontal well, additional events were identified over this part of the section. As a result additional analyses were carried out at 1-foot spacings with the improvement in the zonation indicated by the MV zones and NV zones, where 16 micropalaeontological zones or subzones and 14 nannofossil zones and subzones are recognized over the 50-foot section studied. Some of these zones are only 1 foot in thickness.

A t the w e l l s i te

Mobilization for a well-site assignment can be very rapid as all the equipment required by the micropalaeontologist or nannofossil worker can be hand-carried to the rig.

Foraminiferal microscope work is usually carried out in the logging unit where facilities for washing and drying samples are readily available. Nannofossil work is also ideally undertaken in the logging unit, although occasionally, because of the higher magnification used, excess vibration from the drill floor and shakers may necessitate setting up the microscope elsewhere.

The lag time from the cutting of a sample to its arrival at the shakers can be 1 h or more, and this reinforces the need for a rapid response to any changes. Preparation time takes approximately 5rain with a further 5-10min required

for analysis in the case of both nannofossils and micropalaeontology. The lag time from the cutting of the sample to completion of analysis can therefore be upwards of 1 h, and results are often 100 feet behind the bit depth. However, this is generally within acceptable working, limits, bearing in mind that it is possible to slow down the rate of penetration or to circulate bottom-up samples when necessary.

The biostratigrapher usually tries to analyse every sample collected on the build-section, which can be as close as every 10 feet, to re- affirm the zonal scheme and to identify the correct zonal position at the start of the horizontal section. Once the trajectory is horizontal the sample spacing is usually opened out to 20, 40 or 60 feet depending on the rate of penetration.

It is important for the biostratigrapher to be aware of the angle at which the well is being drilled, and to establish the relationship to the dip of the beds as this can affect the number of fossils recovered. In Fig. 10 a thin bed contain- ing large numbers of a planktonic marker is illustrated. If the well is being drilled along this bed then the marker fossil will appear in abun- dant numbers as in the first case (A). If the well path cuts the bed at an angle then fewer specimens of the marker will appear in the sample (B), and if it cuts the bed at right angles only rare specimens will be recovered (C). It is also important to be aware whether a zone




MV ZONE M ZONE NV ZONE N ZONE

MV11

Ml l NV 20a

N20

z (=3

I.-- c.~ LJ,.J

C./b

(:3 CD I_I_

O L..¢')

MV12a NV 20b

NV 21a MV12b

M12 NV 21b MV12c

MVl2d

MV13a

MV13b

MV14

MV15a

MV15b

MV16

MV17a

MV17b

MV17c

MVlTd

MV18

M13

NV 22a

NV 22b

NV 23a

N21

N22

M14 N23

NV23b

NV 24a M15 N24

M16

NV 24b

NV 25a

NV 25b

NV 26a

NV 26b

M17

M18

N25

N26

Fig. 9. Part of the Valdemar Field zonation over 50 feet of section showing an increased refinement from M (micropalaeontological) and N (nannofossil) zones, where core samples had been analysed at 5-foot spacings, to MV and NV zones, where core samples were subsequently analysed at 1-foot spacings (after Shipp & Marshall 1994).

is being entered from above or below, as the criteria for identifying the zone are likely to be different in each case. For such reasons experience is vital for the successful interpretation of the zonal schemes.

It must be stressed that high-resolution biostratigraphy is only one of several tools available that together make it possible to geosteer a horizontal well. These other tools include 'logging while drilling' (LWD) or 'measurement while drilling' (MWD), hydrocarbon show eva- luation and three-dimensional (3D) seismic (Jeppesen 1994). The well-site geologist, biostratigrapher, MWD or LWD operator, directional driller and company man all form essential ele- ments of the well-site team, which is necessary for the success of any well.

On earlier horizontal wells in the Danish sector a single biostratigrapher carried out the work, but as knowledge of the fields improved so the degree of accuracy required increased. On the Dan Field, for example, the original requirement to stay within the Maastrichtian has changed to more specific requirements such as to follow a particular subzone that correlates to the best reservoir characteristics. In addition, improvements in bit performance has meant that bit trips, which give the palaeontol- ogist an opportunity to rest, are not required so often. Consequently, it was recognized that two biostratigraphers, working 12-h shifts, were required for full 24-h monitoring. Water- injection wells drilled deeper in the reservoir may still only have one biostratigrapher on board, however, as continuous monitoring is less vital.

Case histories

Examples illustrating the contribution made by wellsite biostratigraphy to the drilling of horizontal wells in the Danish sector can be found in the following publications: Anderson et al. (1990), Kruse (1991), Fine et al. (1992), Jeppesen (1994) and Shipp & Marshall (1994).

The authors wish to thank the management of Robertson Research International Limited, the com- panies in the Dansk Undergrounds Consortium (Shell Olie og Gasudvinding Danmark BV, Texaco Denmark Inc. and A. P. Moller) and operator Maersk Olie og Gas AS for their consent to publish this paper and for permission to include some of their data and figures. Some parts of this paper were initially presented at GEO '94 and appeared in Selected Middle East Papers from GEO '94 and we are grateful to the organizers of that conference for permission to include such details in the present updated paper.



84 D . J . SHIPP

Fig. 10. Diagram to illustrate the different number of microfossils, such as planktonic foraminifera, recovered from a thin bed depending on the angular relationship of the bed to the well path. (A) When the well path parallels the bed microfossils are common. (B) When the well path cuts the beds at 45 ° microfossils are occasional. (C) When the well path cuts the beds at a right angle microfossils are rare.

References

ANDERSON, C. & DOYLE, C. 1990. Review of hydrocarbon exploration and production in Denmark. First Break, 8(5), 15 165.

ANDERSON, S. A., CONLIN, J. M., FJELDGAARD, K. & HANSEN, S. A. 1990. Exploiting reservoirs and horizontal wells: the Maersk experience. Schlum- berger Oilfield Review, 2(3), 11-21.

FINE, S., YUSAS, M. R. & JORGENSEN, L. N. 1992. Geological aspects of horizontal drilling in chalks from the Danish Sector of the North Sea. In: PARKER, J. (ed.) Petroleum Geology of North West Europe: Proceedings of the 4th Conference. Geo- logical Society, London, 1483-1490.

INESON, J. R. 1993. The Lower Cretaceous Chalk Play in the Danish Central Trough. In: PARKER, J. (ed.)

Petroleum Geology of North West Europe: Pro- ceedings of the 4th Conference. Geological Society, London, 175-183.

JEPPESEN, M. W. 1994. Geological steering of horizontal wells in chalk reservoirs: examples from the Danish North Sea. Bulletin of the Geological SocieO, of Denmark, 41, 138-144.

KRUSE, I. 1991. Petroleum geoscience - Danish view. First Break, 9(3), 95 106.

SHIPP, D. J. & MARSHALL, P. R. 1994. Biostratigraphic steering of horizontal wells. In: HUSSEINI, M. I. (ed.) The Middle East Petroleum Geosciences. Selected Middle East Papers from the Middle East Geoscience Conference, Bahrain, Volume 2, 849-860.



well-site biostratigraphy of danish horizontal

Documents