The g

ross p

roducin

g in

terv

al in

the

“hig

h v

olu

me a

rea

”has b

een id

entifie

d a

s th

e p

oro

us z

one b

etw

een th

e b

ase o

f the tig

ht,

anhydritic

kars

t an

d a

n in

form

al s

tratig

raphic

mark

er w

e h

ave la

bele

d th

e“x

”m

ark

er, w

hic

h lie

s a

ppro

xim

ate

ly 1

50 ft (4

6 m

)belo

w th

e to

p o

f the S

an

Andre

s F

orm

atio

n.T

his

reserv

oir in

terv

al is

com

po

sed o

f shoal-w

ate

r, oolitic

, fusulin

id, s

kele

tal

gra

insto

nes a

nd p

acksto

nes, c

hara

cte

rized b

y b

iom

old

ic a

nd o

om

old

ic p

oro

sity

with

scatte

red v

ugs a

nd

fractu

res.T

he p

ore

space is

partly

occlu

ded b

y g

ypsum

, makin

g d

istin

ctio

n o

f true p

ore

space d

ifficult d

ue to

the lo

w b

ulk

de

nsity

of g

ypsum

and its

wate

rs o

f hydra

tion. L

og c

om

positio

nal a

naly

sis

was u

sed to

dis

crim

inate

actu

al p

ore

space.

Com

positio

nal a

naly

sis

of th

e c

ore

d in

terv

al o

f the S

an

Andre

s F

orm

atio

n in

well #

1261

was m

ade u

sin

g th

e d

ensity, n

eutro

n p

oro

sity, a

nd b

ulk

photo

ele

ctric

facto

r logs to

solv

e fo

r pro

portio

ns o

f dolo

mite

, anhydrite

, gypsum

, and p

oro

sity.

The s

on

ic lo

g is

agood m

easure

of in

terp

artic

le p

oro

sity, b

ut is

larg

ely

insensitiv

e to

larg

er p

ore

s th

at

occur a

s v

ugs o

r oom

old

s.

The c

om

positio

nal s

olu

tion fo

r the S

an

Andre

s F

orm

atio

n in

well #

1261 w

as u

sed to

com

pute

a v

aria

ble

matrix

transit tim

e, u

sin

g w

eig

hts

that

matc

hed th

e p

rop

ortio

ns o

f dolo

mite

, anhydrite

, and g

ypsum

.T

his

estim

ate

of s

onic

-deriv

ed p

oro

sity

is s

how

n b

elo

w le

ft, togeth

er w

ith th

e p

oro

sity

from

the c

om

positio

nal

analy

sis

and c

ore

measure

ments

of p

oro

sity.

The p

oro

sity

estim

ate

d fro

mcom

positio

nal a

na

lysis

repre

sents

a v

olu

metric

measure

of p

oro

sitie

s o

f all k

inds a

nd

show

s a

good c

on

cord

ance w

ith c

ore

data

.T

he s

onic

poro

sity

is a

clo

se m

atc

h w

ithcom

positio

nal p

oro

sity

in z

ones w

here

all th

e p

ore

space is

pro

bably

inte

rpartic

le, b

ut

show

s d

istin

ctiv

e d

evia

tions in

hig

her p

oro

sity

zones w

here

part o

f the p

ore

space is

vuggy o

r oom

old

ic. In

the k

ars

t zone, th

e s

onic

poro

sity

suggests

that th

e lo

w p

ore

volu

mes a

re d

om

inate

d b

y v

ugs. In

the o

olite

shoal, th

e h

igher p

oro

sity

de

velo

pm

ents

appear to

be a

bou

t equally

div

ided b

y in

terp

artic

le a

nd o

om

old

ic p

ore

space.

The h

igh c

onte

nt o

f anhydrite

and lo

w p

oro

sity

of th

e k

ars

t zone w

as s

trong

ly d

iffere

ntia

ted fro

m th

e m

ore

poro

us s

ectio

n b

elo

wth

e k

ars

t whic

h a

lso a

ppeare

d to

be m

ore

gyp

sife

rous.T

wo lo

g v

aria

ble

s w

ere

used in

dependently

to e

stim

ate

the b

ase o

f the

anhydrite

zone: th

e s

onic

log a

nd th

e a

nhydrite

conte

nt e

stim

ate

d fro

m th

e d

ensity, n

eutro

n p

oro

sity, a

nd p

hoto

ele

ctric

facto

rcurv

es.T

he lo

wer b

oundary

of th

e k

ars

t zone w

as c

alc

ula

ted b

y a

zonatio

n p

rogra

m w

hic

h lo

cate

s z

one

boundarie

s s

uch th

at

varia

bility

is m

axim

ized b

etw

een th

e z

ones w

hile

min

imiz

ing v

aria

bility

with

in th

e z

ones (B

ohlin

g e

t al., 1

998).

PO

RO

SIT

YF

RO

M L

OG

DA

TA

An

app

roxim

ate

ly 2

sq

ua

re m

ile (5

sq

ua

re k

m) a

rea

of W

addell F

ield

, in th

e P

erm

ian

Basin

of w

estTexas, is

chara

cte

rize

d b

y

Op

era

tor-in

terp

rete

d tra

ce

r an

d p

ressu

re d

ata

ind

icate

a h

ighly

co

mp

artm

en

taliz

ed

rese

rvo

irw

ith a

n a

ctiv

e w

ate

r driv

e. R

ese

rvo

irh

ete

roge

ne

ity a

ppe

ars

to b

e re

late

d to

stra

tigra

ph

y a

nd d

iag

ene

sis

, as w

ell a

sa

nh

ydrite

-cem

en

ted k

ars

t fea

ture

s a

sso

cia

ted

with

the s

ub

aeria

l expo

su

re s

urfa

ce

de

velo

pe

d o

n th

e to

p o

f the P

erm

ian

Sa

nA

ndre

s F

orm

atio

n.

The

pre

sen

t stu

dy a

ims to

ch

ara

cte

rize

the

varia

bility

with

in th

e S

an

An

dre

s re

se

rvo

ir by

ma

kin

g u

se

of a

va

riety

of g

eo

log

ica

l,

varia

ble

fluid

pro

du

ctio

n, w

ith o

ve

rall flu

id p

rod

uctio

n a

n o

rder o

f magn

itude g

reate

r than in

surro

un

din

g a

reas o

f the fie

ld.

Re

coverie

s o

f oil a

nd

ga

s fo

r we

lls in

an

d a

djo

inin

g th

is“h

igh v

olu

me a

rea

”ra

nge b

etw

een 1

00 M

BO

E a

nd 1

MM

BO

E p

er w

ell.

Overa

ll, nea

rly 5

0%

of th

e w

ells

pro

du

ce

25

0 M

BO

E o

r less. In

the h

igh v

olu

me a

rea, p

rod

uctio

n is

typic

ally

300 M

BO

E a

nd

mo

re p

er w

ell.

pe

trop

hysic

al, a

nd

geo

physic

al a

na

lyse

s.

In p

artic

ula

r,

Mu

lti-min

era

l mo

de

ls a

re e

sse

ntia

l for e

stim

atin

g e

ffectiv

e p

oro

sitie

s th

at p

rovid

e g

ood m

atc

hes w

ith c

ore

.

Sta

tistic

al z

on

atio

n o

f we

ll log

s p

rovid

es a

co

nsis

ten

t meth

od fo

r identify

ing th

e b

ase o

f kars

t.

Seis

mic

horiz

on

map

pin

g p

rovid

es d

eta

ils o

n th

e c

on

figura

tion o

f the re

se

rvoir in

terv

al.

Seis

mic

imp

eda

nce

allo

ws u

s to

de

term

ine

inte

rwe

ll po

rosity

varia

tion.

BV

W p

rofile

an

aly

sis

is u

se

ful fo

r asse

ssin

g s

pa

tial c

on

tinu

ity o

f the re

serv

oir.

Mu

lti-trace

se

ism

ic a

ttribu

tes, s

uch

as v

olu

me

tric c

urv

atu

re, p

rovid

e a

dde

d d

eta

il in o

ur in

terp

reta

tion o

f reserv

oir

com

pa

rtme

nta

lizatio

n.

iiiiii Asig

nific

an

t nu

mb

er o

f ca

rbo

na

te re

se

rvo

irs w

orld

wid

e h

ave b

een m

odifie

d b

y k

ars

t. Kars

t can im

pact re

serv

oir p

erfo

rmance

eith

er b

y e

nh

an

cin

g o

r de

stro

yin

g p

oro

sity

/pe

rme

ab

ility.

We in

tegra

ted

co

re, lo

g, 3

D s

eis

mic

, an

d p

rod

uctio

n d

ata

to id

entify

the n

atu

re, d

istrib

utio

n, a

nd im

pact o

f kars

t in a

Perm

ian

San

An

dre

s c

arb

ona

te re

se

rvo

ir in W

ad

de

ll Fie

ld, w

estTe

xa

s.T

he re

serv

oir in

our s

tudy a

rea is

hig

hly

com

partm

enta

lized a

nd flu

idp

rod

uctio

n is

extre

mely

va

riab

le. R

ese

rvo

ir he

tero

ge

ne

ity a

ppe

ars

to b

e re

late

d to

stra

tigra

phy a

nd

dia

gen

esis

, as w

ell a

s k

ars

tfe

atu

res a

sso

cia

ted w

ith a

su

ba

eria

l exp

osu

re s

urfa

ce

at th

e to

p o

f the

San

Andre

s F

orm

atio

n. C

ore

data

indic

ate

that th

eu

pp

erm

ost S

an

An

dre

s c

onsis

ts o

f sp

ora

dic

ally

po

rou

s“m

acro

”kars

t, chara

cte

rized b

y in

ten

se c

ha

otic

bre

ccia

tion a

nd a

nhydrite

rep

lace

men

t, follo

we

d b

y is

ola

ted

, late

sta

ge

an

hyd

rite d

issolu

tion.T

he k

ars

t overp

rints

hig

h fre

que

ncy s

equence

s c

om

pose

d o

fg

yp

sife

rous o

olitic

, fusulin

id, a

nd

ske

leta

l pa

cksto

ne

-gra

insto

ne

reserv

oir ro

ck w

ith m

old

ic, v

ug, a

nd

fractu

re p

oro

sity. W

e u

sed

wire

line lo

g p

etro

physic

al s

olu

tion

s to

qu

an

titativ

ely

dis

crim

inate

the a

nhydritic

kars

t from

the u

nde

rlyin

g p

acksto

ne-g

rain

sto

ne

stra

ta in

unco

red

we

lls.T

he b

ase

of th

e k

ars

t zo

ne

co

rrespond

s to

a s

harp

de

cre

ase

in s

eis

mic

imp

edance, a

nd 3

D s

eis

mic

data

are

used to

ma

p th

e b

ase

of k

ars

t be

twe

en

we

lls.

Th

e k

ars

t zo

ne e

xh

ibits

hig

h v

aria

bility

in th

ickne

ss; h

ow

ever, th

e z

on

e is

ge

nera

lly th

icke

r on h

igh

er p

ortio

ns o

f a S

E-tre

nd

ing

an

ticlin

e th

at ru

ns th

roug

h th

e s

tudy a

rea, s

ug

gestin

g a

stru

ctu

ral c

ontro

l on

ka

rst d

eve

lop

me

nt. S

eis

mic

da

ta s

ho

w th

at th

e k

ars

t zo

ne

trun

cate

s th

e b

ase

of th

e p

oro

us re

serv

oir in

so

me a

reas a

nd

seis

mic

attrib

ute

s re

vea

l po

ten

tial re

se

rvo

ir co

mp

artm

en

t bo

un

da

ries. B

ette

r unders

tandin

g o

f local k

ars

t co

ntro

l on flu

id flo

w in

this

reserv

oir c

an

imp

rove re

serv

oir m

an

ag

em

en

t de

cis

ion

s. A

BS

TR

AC

T

Pe

trop

hy

sic

al a

nd

Ge

op

hy

sic

al C

ha

rac

teriz

atio

n o

f Ka

rst

in a

Pe

rmia

n S

an

An

dre

s R

ese

rvo

ir, Wa

dd

ell F

ield

, We

st T

exas

Su

san

E. N

issen

, Jo

hn

H. D

oveto

n, a

nd

W. L

yn

n W

atn

ey

12

2

12

Ge

op

hysic

al C

on

su

ltan

t, Mc

Lo

uth

, KS

;K

an

sa

s G

eo

log

ical S

urv

ey, U

niv

ers

ity o

f Kan

sa

s, L

aw

ren

ce, K

S

BA

CK

GR

OU

ND

AN

D P

UR

PO

SE

OF

ST

UD

Y

The s

eq

uence fra

mew

ork

for th

e U

pp

er P

erm

ian (G

uadalu

pia

n) S

an

Andre

s F

orm

atio

n is

based o

n th

e s

tudy o

f surfa

ce e

xposure

s in

the G

uadalu

pe M

oun

tain

s o

f WestTexas.T

he

dolo

mitic

reserv

oir in

Waddell F

ield

is c

om

pris

ed o

f cyclic

oolitic

gra

insto

nes, s

pecific

ally

G8 a

nd G

9 h

igh fre

que

ncy s

equence

s (H

FS

) belie

ved to

be 4

th-o

rder (0

.1-1

Ma

)perio

dic

ity (F

rench a

nd

Kera

ns, 2

004

). In th

e“h

igh v

olu

me a

rea

”, the re

gio

nal s

trata

lbounda

ry th

at s

epara

tes G

8 fro

m G

9 h

as n

ot b

een

pre

cis

ely

loca

ted a

nd tie

d in

to th

ere

gio

na

l stra

tigra

phic

fram

ew

ork

.

The G

8 a

nd G

9 H

FS

reserv

oir in

terv

al o

verlie

s a

regio

nal b

ypass s

urfa

ce c

orre

spondin

g to

the to

p o

f the B

rushy C

anyon in

the o

utc

rop (a

lso e

quiv

ale

nt to

the to

p o

f G4 H

FS

).In

terp

reta

tions o

f surfa

ce e

xposure

s o

f these s

trata

indic

ate

that th

e in

ner a

nd m

iddle

ram

plith

ofa

cie

s d

urin

g th

e G

8 H

FS

underw

ent b

ackste

pp

ing, w

hile

the

G9 H

FS

was in

volv

ed in

forw

ard

ste

ppin

g, re

flectin

g re

lativ

e fa

ll in s

ea le

vel (F

rench a

nd K

era

ns, 2

004).

These

observ

atio

ns, c

ouple

d w

ith s

eis

mic

inte

rpre

tatio

ns o

n th

e e

aste

rn e

dge o

f the C

entra

lB

asin

Pla

tform

(Qife

ng

Dou, p

ers

. co

mm

.), suggest th

at th

e s

ucce

ssio

n o

f oolitic

shoals

inW

addell F

ield

are

com

pris

ed o

f a re

trogra

datio

nal to

aggra

datio

na

l to p

rogra

datio

nal s

trata

l arc

hite

ctu

re re

su

lting in

south

eastw

ard

late

ral a

ccre

tion o

f a s

hallo

w s

helf th

rough W

addell F

ield

tow

ard

the e

aste

rn m

arg

in o

f the C

en

tral B

asin

Pla

tform

.

ST

RA

TIG

RA

PH

ICA

NA

LY

SIS

AN

DP

ET

RO

PH

YS

ICA

LC

HA

RA

CT

ER

IZA

TIO

N

Stra

tigra

ph

ic c

olu

mn

for u

pp

er L

eo

na

rdia

n a

nd

low

er

Gu

ad

alu

pia

n s

ec

tion

in th

e P

erm

ian

Ba

sin

.A

fter R

up

pe

la

nd

Be

bo

ut (2

00

1).

GE

OL

OG

ICA

LS

ET

TIN

G

BB

'

Atim

e s

truc

ture

ma

p o

f the

top

of th

e G

ray

bu

rg fro

m a

3D

se

ism

ic s

urv

ey

ov

er W

ad

de

ll Fie

ld s

ho

ws

the

reg

ion

al

stru

ctu

ral c

on

figu

ratio

n. T

he

bla

ck

bo

x h

igh

ligh

ts th

e“h

igh

vo

lum

e a

rea”

stu

dy

are

a.

Sim

plifie

d g

eo

log

ica

l ma

p o

f the

Sa

nA

nd

res

Fo

rma

tion

in th

eP

erm

ian

Ba

sin

sh

ow

ing

loc

atio

ns

of m

ajo

r oil fie

lds

(Sc

ho

lle,

http

://ge

oin

fo.n

mt.e

du

/sta

ff/sc

ho

lle/g

ua

da

lup

e.h

tml; a

fter W

ard

et a

l.,19

86

). Ou

r stu

dy

are

a is

in W

ad

de

ll Fie

ld, n

orth

ern

Cra

ne

Co

un

ty, T

X, lo

ca

ted

on

the

ea

st c

en

tral fla

nk

of th

e C

en

tral

Ba

sin

Pla

tform

.

Stu

dy

Are

a

Delaware Basin

Cra

ne

Central BasinPlatform

Midland Basin

1 m

i

A

A’

Su

bs

ea

de

pth

ma

p o

f the

top

of th

e S

an

An

dre

s F

orm

atio

n fo

r the

“h

igh

vo

lum

ea

rea

”o

f Wa

dd

ell F

ield

.

Stru

ctu

rally, th

e“h

igh v

olu

me a

rea

”of W

addell F

ield

is lo

cate

d o

n th

e e

ast

centra

l flank o

f the C

en

tral B

asin

Pla

tform

.

The n

orth

west p

ortio

n o

f the

“hig

h v

olu

me a

rea

”is

stru

ctu

rally

hig

her th

an

are

as to

the s

outh

and e

ast, a

lthough

the h

ighest s

tructu

re d

oes n

ot

corre

spo

nd to

the h

ighe

st p

roductio

n.A

south

east-tre

ndin

g p

lungin

g a

ntic

line

appro

xim

ate

ly tw

o m

iles lo

ng c

rosscu

ts th

e s

tudy a

rea, s

ho

win

g a

relie

f of

appro

xim

ate

ly 7

5 ft (2

3 m

) and a

wid

th o

f appro

xim

ate

ly o

ne m

ile (1

.6 k

m).

Ashallo

w s

addle

in th

e c

entra

l mapped a

rea e

xhib

its e

levate

d g

as a

nd to

tal

fluid

pro

ductio

n.

Se

ism

ic p

rofile

ac

ros

s th

e s

he

lfm

arg

in o

f the

Ce

ntra

l Ba

sin

Pla

tform

sh

ow

ing

refle

cto

rc

on

figu

ratio

ns

tha

tle

ad

to th

ein

terp

reta

tion

of th

eG

4 to

top

Sa

nA

nd

res

as

atra

ns

gre

ss

ive

sy

ste

ms

trac

t an

dth

e to

p S

an

An

dre

sto

Gra

yu

rg a

s a

hig

hs

tan

d s

ys

tem

stra

ct.

A-A

’

Gra

yb

urg

To

po

fS

an

An

dre

sG

4u

nco

nfo

rmity

G3

un

co

nfo

rmity

HS

T

TS

T

HS

T

TS

T

A’

A

Cu

mu

lativ

e o

il an

d g

as

(left), c

um

ula

tive

tota

l fluid

(oil+

ga

s+

wa

ter) (c

en

ter), a

nd

cu

mu

lativ

e g

as

(righ

t) ma

ps

inb

arre

ls o

f oil e

qu

iva

len

t (BO

E) s

ho

win

g.A

co

nv

ers

ion

fac

tor o

f 5.7

MC

F g

as

to o

ne

eq

uiv

ale

nt b

bl o

f oil w

as

us

ed

in th

e c

on

ve

rsio

n to

BO

E.

the

“h

igh

vo

lum

e a

rea”

of W

ad

de

ll Fie

ldD

ep

th c

on

tou

rs fo

r the

top

of th

e S

an

An

dre

sF

orm

atio

n a

re s

up

erim

po

se

d.

LIT

HO

FA

CIE

SC

ore

s o

f the u

ppe

r San

Andre

s F

orm

atio

n w

ere

taken fro

m tw

o w

ells

with

in th

e“h

igh

volu

me a

rea

”, W. N

. Waddel #

1204 a

nd W

. N. W

addell #

1261. C

ore

descrip

tions

pro

vid

ed b

y th

e o

pera

tor in

dic

ate

an u

pper k

ars

t inte

rval in

these w

ells

invo

lvin

gm

acro

scopic

colla

pse a

nd c

haotic

bre

ccia

tion a

nd e

xte

nsiv

e a

nhydrite

repla

cem

ent o

fgypsum

in th

e u

pper S

an

Andre

s F

orm

atio

n. In

contra

st, th

e“p

oro

us k

ars

t zone

”and

“kars

ted a

nd b

iotu

rbate

d fu

sulin

id s

hoal”

belo

w th

e m

ain

kars

t zone in

well #

1204 is

less

inte

nsely

kars

ted, w

ithout m

acro

-scale

chaotic

bre

ccia

tion a

nd a

nhydrite

repla

cem

ent.

This

cm

-scale

dis

solu

tion a

nd b

reccia

tion is

recogniz

ed h

ere

as

“mic

ro”

kars

t where

the

matrix

is e

ssentia

lly in

tact.

The m

atrix

pro

pertie

s in

the m

icro

kars

t inte

rvals

are

als

opro

bably

dom

inan

t in te

rms o

f fluid

flow

.T

hus, th

e lo

wer k

ars

ted z

ones in

well #

1204 a

repla

ced in

the in

situ

bedded c

arb

onate

reserv

oir o

f the S

an

Andre

s F

orm

atio

n.

An

ex

am

ple

of th

e re

su

lts o

f the

ka

rstic

zo

ne

me

tho

do

log

y is

sh

ow

nfo

r the

co

red

we

ll #1

26

1 w

ell a

nd

two

ne

igh

bo

ring

we

lls. In

we

ll#

12

61

, the

co

re d

es

crip

tion

su

bd

ivis

ion

of th

e u

pp

er S

an

An

dre

sF

orm

atio

n b

etw

ee

n th

e k

ars

t zo

ne

an

d p

oro

us

, oo

litic s

ho

al fa

cie

s is

clo

se

ly m

atc

he

d b

y th

e z

on

atio

n p

ick

s b

as

ed

on

the

so

nic

an

de

stim

ate

d-a

nh

yd

rite lo

gs

. No

te th

e s

ign

ifica

nt v

aria

tion

in th

ick

ne

ss

of th

e in

terp

rete

d k

ars

t zo

ne

in th

e th

ree

we

lls.

Estim

ate

s o

f the d

epth

of th

e b

ase o

f the lo

w-p

oro

sity

zone a

nd a

nhydrite

phase a

t the to

p o

f the S

an

Andre

s F

orm

atio

n w

ere

com

pile

d fo

r all w

ells

with

density, n

eutro

n, p

hoto

ele

ctric

facto

r, and s

onic

logs. In

wells

where

only

a s

onic

log w

as a

vaila

ble

, the e

stim

ate

was re

stric

ted to

the b

ase o

f the

low

-poro

sity

sectio

n.

Genera

lly, the th

ickness o

f the lo

w p

oro

sity

Kars

t zone is

gre

ate

st o

n th

e s

outh

east-

trendin

g a

ntic

line th

at c

uts

thro

ugh th

e“h

igh

volu

me a

rea

”. How

ever, th

is z

one s

how

shig

h s

patia

l varia

bility, p

unctu

ate

dby a

nom

alie

s w

here

the

"kars

tic" in

terv

al is

eith

er m

ark

edly

thic

k o

r thin

. In a

few

wells

,th

ere

was n

o e

vid

ence o

f a lo

w-p

oro

sity,

anhydritic

zone a

t the to

p o

f the S

an

Andre

sand th

is w

as in

terp

rete

d a

s a

n a

bsence o

fkars

t develo

pm

ent.

1207

1228 1

204

1261

B’

B

Iso

pa

ch

ma

p o

f up

pe

r tigh

t zo

ne

of S

an

An

dre

s F

orm

atio

n in

terp

rete

d a

s k

ars

t,w

ith to

p o

f Sa

nA

nd

res

Fo

rma

tion

su

bs

ea

de

pth

co

nto

urs

su

pe

rimp

os

ed

.