dynamic reservoir characterization

8/9/2019 Dynamic Reservoir Characterization

1/14

Colorado Scho

ol

of Mines

Fundamentals in Well Log

Interpretation

GPGN 532 -A

Final

project

ba

sed

on the

paper:

Dynamic Reservoir Characterization

of a C02 Huff'n'Puff.

Central Vacuum Unit, Lea County New Mexico

Davis T.L., Ben

so

n R.D ., Roche

S.

L. and Sc

uta

M.S.; 1

7, Expanded

bst

racts S

PE

Inter

na

t ional Meeting)

Efrai n Mendez

Golden,

December 3, 1998


2/14

EXECUTI VE SUMMARV

Oyoamic Rcserv

oir

Characlerizalioo can be notably enhanced by the use

of 40,

3C

sc ismology. Afier a feasibility analysis, thi s technology can be applied to monitor fluid

front movements during

field

production and lO determine the variability, with

in rock/fluid properties of the reservoir. rhe improved reservoir characterization will

increase the hydrocarbon recovery, reducing operaling costS with a resulting better

reservoir management. The end resull is ncreased reserves produced al a lower COSI

OBJE IVE

OF

THI S TECHNICAL REI)ORT

/ ro describe the methodology known

as

40, 3C seismology, ils basic principies,

applications and economic j ustificalion 10

be

applied in reservoir characlerization

CONTENTS

40,

3C Seismology.

What

does it mean ?

11. Physical principies and imp1ementation

III. Application

IV. Economic justification

V. Conclusions and Recommendations

40, 3C SEISMOLOGV. WHAT DOES IT MEAN?

11

is

well known that Ihreedimensional

30)

seismology has been

{he

most impacting

e..

technology over Exploration and Production industry during last years. Today, 3D

ttd; seismic shows high costlbenetit ratios by reducing the dry-hole

ris

k as well as

by

m improving the fie ld development and production strategies. Conventional 3D seismic

= : : 1 1 : 0 ~ : c : ~ ~ ~ o : : ~ : m : d s o : ; ~ ~ i ; h : p ; : : : h r e : : i : : : ~ U 1 P ~ : a i : : n ~ ~ : r ~ : :

: :::

framework and some stratigraphic features ofthe reservoirs . Nowadays, new altcmalives

in the knowledge of reservoir rack and fluid properties come out by the combined use of

- three component (3C) seismic data, tha is, by using compressional and shear waves,

acquired during 3D, 3C seismic surveys.

Oynamic: Reservoir Charoc:te";zGtioo

Efrojn

e n

u

bec: 3. 1

99

8


3/14

Recently, the time as the fourth dimension, has been added to this technology oblaining

whal we know as 40 (time lapse), 3C sei smology . This powerfullool consists in the

repeated acquisition

of

30, 3C seismic surveys. over producing fields, with the

pUrpse

of monitoring fluid movemcnts and changes

in

reservoir properties by comparing Ihe

seismic response from each other survey.

Ahhough this is nOI

yet

a matute technology, Ihe increascd hydrocarbon recovery and

reduction in operating costs

are

doing Iha140, 3C seismology hegins to be recognized as

an integral part of dynamic reservoir characterizalion. As Rbonda Duey (1998) said,

Someday 4D seismic lechnology may be used as routinely as 3D seismic is toclay.

11. BA81C PRJNCIPLES AND IMPLEMENTATION

In

exploration seismology. two body waves are generated artificial1y propagating through

the

subsurface with different mode of propagalion related to the nature of rock

defonnation (Figure 1

.

According to Hook 's Law, eaeh wave stresses the rock inducing

a strain proportional 10 the stress. Ouring thc passage ofthe primary or eompressional (P)

wave, Ihe rock changes volume but nol shape in response to altemaling compressive and

tensional stresses whereas, with

the

trave1-path of Ihe slower secondary or shear (8)

wave, the rock changes shape but not volume (Danbom, 1986).

The magnitudes

ofthe

velocides

Vp

and

V r

are influenced by the elastieily

oflhe

A ~

w

d

they are travelling. With isotropic media p provides a measure of the bulk rock

compressibility, rigidily and dcnsity, whereas

Vs

is

sensitive to rigidity

and

density.

As

wc know, 8 waves can not propagate in a

fl

uid (rigidity equals to zero). ~ hand,

Ihe

ratio p s appears strongly correlated with the reservoir produclion charaeteristies,

showing a strong dependence on porosily and playing an important

rol

e

in

seismic

interpretadon nol only as lithology identifier but also for anisotropic inlensity estimation.

Al]

rock systerns are anisotropie

lO

sorne degree. rneaning thal one o' more physical

properties ehange as they are mcasured in differenl directions. The effect of

r o p y on

P wave trave1tirnes is usually small, however S waves exhibit splitting

b i r e f ~ n c e

thut

is,

depcndenec of velocity on the dircclion ofpolarization. n a fractured medium, the

incident S wavc splits into two components, a fasl 81 and a slow

S2

(Figu re 2 . Thc

[)ynamie Reservoir Ch(U '(lcteri:zation

efra

l MemH:Z

t ec 3, 1998


4/14

degree of splitting gives a rough measure oflhe fracture intensity (Figure 3), whereas the

polarization

of

the [aster SI wave

is

generally parallel

to

the str

ike of

the fractures.

Fractures are probably he mosl importan anisolropic property in fluid flow because they

cause/ several rock properties, such as penneability,

10

have difIerenl values parallelto

the fracture planes Ihan Ihey do perpendicular ~ ~ ~

~ / U

This clcar dependence 00 fluids and fracturing i o m p o n n t seismology valuablc

for the reservoir engineer (Figures 3

10

5). Now, by cxtending Ihis knowledge,

he

differences between successivc seismic surveys will indicatc changes

in

producing

rescrvoirs, such as fluid m o v e m

J

~ the change of reservoir properties., mainly

pcnneability, with

tlIt.

time. Davis ft (1997), refers "The penneability of a fonnation, or

the corme


5/14

program in Vacuum field , New Mexico (Figure 6). The main objective

is

to demonstrate

the capability of repeated (time-Iapse) 3D, 3C seismology to detect

and

monitor changcs

in

rock/fluid properties assoeiated with the CO

2

injection, soak, and wilhdrawal ("puff"

or produclion phase) processes.

Vacuum Field is located on a arge E-NE anticJina Slructure. The San Andres and

Grayburg fonnalions eorrespond

10

the rim of a broad carbonate shelf province to the

north and northwesl, and the rim of a deeper intraeralonic basin, on Ihe southeast and

easl. San Andres carbonates at depths from 4200ft to 4800ft are Ihe main produclion

zones. The producing interva shows average porosity of 11.6% and average penneability

of22.3md, wilh an initial reservoir pressure of 1628 psia at 4500ft. Reservoir pressure

Is

maintained aboye Ihe bubble point pressure (764 psia) by waterflooding. The production

data suggest an effective penneabilily pathway extending northwesl from CVU-97 where

the reservo r tends 10 higher produclions than in the soulheasl portion

of

he mapped area.

In

Ihis sense Ihcre is a SW to NE trend thal separales a higher production rone in the NW

portion from a ower perfonnance

in

the SE portion.

The

C h

"huff-n-pufl" occurred in well CVV-

97.

A base 3D, 3C SUlvey (Oclober 28 10

Novembcr 13, 1995) was shot prior

10

injection, which occurred from November 13

10

Oecember

8.

The "soak" period extended from Deccmber 8 to December 28, afier which

Ihe wetl was relumed lo produclion. A second 3D, 3C survey was acquired from

December

21 10

Oecember 28 during the "soak" periodo

Ouring th e injection process and "soak" periad the reservoir pore pressure and fluid are

altered. lllercfore, severa dynamic changes 10 the reservoir propenies between the base

and repeated surveys are expected. Examples of P and S migraled seclions before and

after the inj ection program revel seismic di fferences

in

the signal (Figure

7)

. Time-Iapse

interpretation consisted in manipulating th ese differences to reveal characteristics of the

dynamic response of the bulk rock/fluid properties lo the changing reservoir conditions

The P and S waves show a CO

2

bank fonned to the sou

th of

injection well. In this sense,

a P wave amplitude anomaly (Figure 8) an d a shear wave anisotropy anomaly (Figure 9)

coincide with the Ol bank. The polarization angle of SI also confinns the regional

maximum horizontal stress direction. The velocity anisotropy anomaly can e explained

Dyl lOmic: I

l:I:.serYOir CMr


6/14

by variations

in

pore pressure which could affee

the

percentage of open fractures

affecting the degree of shear wave splitting. Also changes in fluid viscosity may affect

the wettability ofthe rock frame and rigidity

of

this type

of

media.

Pore pressure changes and variations in fluid properties have produced a multicomponent

40 signature detectable using the seismic data. t can be considered a significant advance

in

geophysical applications toward reservoir monitoring.

IV. ECONOMIC JUSTIFICATION

After he feasibility analysis has dictated a "good candidate reservoir for 40 3C

seismology", the economic justification can

e

supported considering that the data

obtained may e used to enhance hydrocarbon reeovery, revitalize old fields, reduce

operation wsts, prolong well life andlor change production slrategies. Even more, new

well localions can be pro)Xlsed by identifying bypassed accumulations in the interwell

regions where only seismic data can provide infonnation.

Ideal1y enhanced acquisilion repeatability should consider the sume acquisition method

for each survey and accurate source and receiver positioning (perhaps even using a

pennanent receiver installation). These aspccts should also tend lo deerease the eosts for

each new repeated survey. The end result is inereased reserves produced at a lower cost ,

V. CONCLUSIONS ANO RECOMMENOATlONS

40 3C seismology can help to make better decisions and simulate scenarios

to

optimize production, improve oil rewvery and reduce costs. Better reservoir

management can e achieved

by

updating and improving the static and dynamic

reservoir model periodically.

Project success in a 40 3C seismology campaign requires

tha!

a change

in

petrophysica[ fluid propenies will change the seismic response

of

the reservoir. A

feasibility analysis will hclp

lo

make decisions about the implementation of this

teehnique under particular cond itions.

Oynamic Reservoir Characterization is a multidisciplinary teehnology that needs not

onJy

the se ismic interpretation but also the integrated analysis ofborehole and

production data, reservoir simulation and modeling.

Dynornic

Rescrvoir Chorocterizotion

Efrain Mendez

cc 3. 1998


7/14

REFERENCES

l. Arestad J.F., Davis T.L. and Benson R.O.; 1996, "Utilizing 3-D, 3-C Seisrnology for

RescIVoir Property Characterizalion al Joffre Field, Alberta, Canada". Applications

of

3-D

Seisrnic Data

to

Exploralion

and

Production. Edited

by

Weirner P. and Davis T.L. AAPG

Studies

in

Geology,

No.

42-5EG Geophysical Developrnents Scries, No . 5, p. l7 l-1

78

2. Danborn S.H. and Dornenico S.N .; 1986, "Shear Wave Exploraton". Geophysical

Developrnenl Scrics, V.l Sodety

of

Exploration Geophysicists.

3 Davis T.L., Denson R. D., Roche S.L., and Scuta M

.S.; 1997,

"Dynamic

ReseIVoir

Characterizalon of a COl Huff' n' Puff, Central Vacuurn Unit, Lea County, New e x i c o ~

Expandcd Abstracts, 1997 Annual Technical Conference and Exhibition, Sociely of

PetroleumEngineers, l

nc.

4. Duey R., 1997; "4D Seismic on Cuning Edge of ReseIVoir Monitoring Technology". Hart's

Show Special Edition, AAPG Annual Convcntion

5. Ehrorn D., Shcriff R. E., 1992; "Anisotropy and ReseIVoir Development". Reservoir

Geophysics, Invesligations

in

Gcophysics

No.

7. 50ciety ofExploralion Geophysicists

6. King G.; 1996, "4-D seisrnic improves reseIVoir rnanagement decisions. Parts I and 2",

World Oil, MaTCh and April1996

7. Hardage B.A.; 1996, "Combining P-Wave and S-Wave Seismic Dala to lmprove Prospect

Evalualion". Report oflnvesligations No. 237, Bureau ofEconornic Gcology, T

he

University

ofTexas atAustin

8. Lurnley D.E., Behrens R.A. and Wang

l ;

1997, "Assessing

Ihe

technical risk of a 4-D

seismic project". The Leading Edge,

16,

p.1287- 1

291

9. Mueller M.C.; 1992, "Using shear waves to predict laleral variability

in

vertical fracture

intensily". The Leading Edge, II,p.29-35

\O. Nestvold E.O.; 1996, "T

he

impact of 3-D Se ismic Data on Exploration, Field Development,

and Production". Applicatio ns

of

3-D Seismic Data

10

Exploration and Production. Edited by

Weimer

P.

and Davis T .L. AAPG Studies in Geology,

No.

42-5EG Gcophysical

Developments Series,

No.

5 p.I -7

. Peeters M.; 1998, "From Pictures 1 Properties". Paper

presente

on the inauguration of the

Baker Hughes Distinguished Chair of Petrophysics Borehole Geophysics". Colorado

SchoolofMines

12.

Wang Z

.;

1997, "Feasibility oftirne-Iapse scisrnic reseIVoir monitoring: The physical bas is".

The LeadingEdge, 16,p.1327-1 329

13. 1997, 1998, "Reservoir Characterization Project, Phases VI and VII". Final

Reports. Colorado School ofMines

[)yno.lTl

ie

R u ~ t V ( I i r Charaetari:ZOotion

frain

Mende.:z

[ ae 3,1

99


8/14

C

P

WAVE

----, :

I I I

I I

i 1

, ,

L _

J

L

.J

Comp r

eulon

Teosion

S-WAVE

~ :

,

=

__J

Clockwl,.

Fig.

1.

Distortion

of

an elementary cube

of

a medium caused

by

passage

of

a

P

wave (above) and an S wave (below). (Danbom, 1987)

Fig. 2. Principies

of

S wave splitting in a fractured rack medi

um.

The

incident S wave spl its into two compone

nt

s, the fast SI polarized in

th

e

direction

of

the maximum horizontal stress

a ,)

whereas S2 is polarized

in the direction

of

minimum horizontal stress

cr

min)

(Hardage, 1996)


9/14

Fig. 3. Spa

ti

a

ll

y coincidem P and S wave seismic sequences. Note that even

mough each sequence spans three identical black peaks on

me

right si de

of

each image, the internal architecture

of

the S wave sequence allows providing

more

in

f

onna

tion about reservoir flow paths and compartmem boundaries.

(Hardage, 1996)

4.7

4.8

4.

5 .0

51

5 2

5.3

5.4

4.7

4.8

4.

5 .0

5. 1

5.2

5 3

5.4

Fig. 4. S and 8

2

images across [he Austin Chalk. The 8

2

reflect

io

n is delayed

by

about 50msec rclative lo S. reflection. No

te

the prominent amplitude

anomaly towards the middl

e.

This represents a highly fractured zone 250m

wide. This efTect appears with consistent ampl itude on

me

S.. whereas on the

S

section, the Austin Cha

lk

shows laterally variant amplitudes (Mueller, 1992)


10/14

Fig

5. Velocity ratio map

VpfVs

computed from

th

e

S

and P datasets)

for Nisku carbonate reservoir interval, Joffre Field, Albena, Canada. Core

porosity contours overlap VpfVs. B

lu

e and magenta colors show higher

VpfVs zones which strongly agree with the highesl porosity v

lu

es.

Areslad, 1996)


11/14

g 6 Location map o Vacuum Field. Lea County, New Mexico.

Colorado School ofMines, 98)


12/14

,

. , 1 '- t:'.H ~ f 1 1 ' 1 1 ~ 3 '

I - _ ..

- I _

' < . ~ ~

"

; 1

." . ...

'.

n '

: - r ~

1 1) : _ I

' " ;

1

111

1

t -, '' ' . , ' I : : ; ~ 1 ~ _ .

~ . ,

.... ..

' I ~ I V ' ' ' ' ' ' ' : ; ; ; ; J .

,... - "

L

___

- - I _ _

li r,] - , ,:t

(a)

J..... : : : : .... ~ , . . , : : . : : - ~ : : ' : : ' , , : ~

::

f ; ~ E i ~ ,

J

~ + t : ~ ' ~

-

: - -.

- 'O- ..... _

(b)

-

= " ~ - = : ~

: - ~ : : _ .

. . ~ : ... :i; .;.;.

,-ir

~ ~ ~ f H f ~ ~

I

~ r ~

~ \ :

-r ..

~ ' . :

- - : ..c. ..

(e)

Fig. 7. lnline 69 (migrat

ed

sections). (

a)

P

wave

from

the in itial and

re

peat surveys

(0 .1 0

10

1.65s);

(b)

SI wave (po larizati

on:

118) and S2 wavc (polarization: 28)

from

the initial survey (0.5

to

3.25s); (e)

SI

wa ve

(polarization: 118) and S2

wave

(polarization: 28)

from

the rcpeal survey

(0 .5 to 3.25s). (Davis, 1997)


13/14


14/14

dynamic reservoir characterization

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