SAN ANDRES-GRAYBURG STRATIGRAPHY AND FACIESFuhrman-Mascho Field

CYCLE STRATIGRAPHY AND FACIES ARCHITECTUREFuhrman-Mascho San Andres Field, Andrews County, Texas

SAN ANDRES-GRAYBURG STRATIGRAPHY AND FACIESFuhrman-Mascho Field

MIDDLE PERMIAN SEQUENCE STRATIGRAPHYPermian Basin

MIDDLE PERMIAN SEQUENCE STRATIGRAPHYPermian Basin

QAb3743c

WesternDelaware

Basin

BrushyCanyon

CherryCanyon

Cutoff

BoneSpring

Cherry Canyon

WesternEscarpment

Queen

Grayburg

Cutoff

upperVictorio Pk

lowerVictorio Pk

Queen

CentralBasin

Platform

upperSan Andres

Grayburg

lowerSan Andres

Glorieta

Clear Fork

BrushyCanyon

equivalent

Holt

McKnight

WesternMidlandBasin

Queen

upperSan Andres

Grayburg

upperSan Andres

AlgeritaEscarpment

Grayburg

lowerSan Andres

Yeso

Highfreq.seq.S

erie

sL

EO

NA

RD

IAN

L7L8G1G2G3

L6

G4

G5

G6G7G8G9

G10G11G12G13

G14

Relativesea level

Glorieta

Clear Fork

low

erS

an A

nd

res

GU

AD

AL

UP

IAN

Fall

G15

G16

3. Comprehensive study of the San Andres and Grayburg Formations in outcrop in the GuadalupeMountains by Kerans and co-workers shows that the San Andres platform carbonate succession isdivided by a major uniformity representing at least 100 m of sea-level fall.

low

er S

an A

ndre

sco

mp.

seq

uenc

eup

per

San

And

res

com

posi

te s

eque

nce

Hiatus

TEXAS

NEWMEXICO

MEXICO

Studyarea

VacuumHanford

SeminoleWest

SeminoleNorth

Robertson

Means

Martin

Mabee

Gaines

EmmaEctor

Foster

Goldsmith

Harper

DuneMcElroy

Waddell

Penwell

DE

LAW

AR

EBASIN

BASIN

MID

LA

ND

Fuhrman-Mascho

NORTHERN SHELF

EASTERN

Slaughter

CE

NT

RA

LB

AS

INPLATFO

RM

SHELF

QA12908(a)c

Upton Reagan

Irion

Crockett

Terrell

Ward

Winkler

Pecos

AndrewsMartin Howard

Dawson Borden

Glasscock Sterlng

Mitchell

Scurry

Kent

Dickens

GarzaLynnTerryYoakum

Cochran Hockley Lubbock Crosby

Midland

Gaines

LovingReeves

Sutton

Schleicher

Tom Green

Coke

Nolan

Fisher

N

0

0

20 40 mi

4020 60 km

San Andres/Grayburgfields ≥ 10 MMbbl production

OZONA

ARCH

Lea

TEXAS

NEW MEX

Fuhrman-Mascho

C.I. 50 ft

STUDY AREA

0 10,000 ft

300 m0

Structural high(>-1150')

PSL A-42

-1100

-110

0

-1300

-120

0

-1000

-1100

-1200

-1100

PSL A-43

UNIVERSITY LANDS

BLOCK 9

FUHRMAN-MASCHO FIELD

UNIVERSITY LANDS

BLOCK 10

-120

0

EMMA FIELD

QAc1874c

PSL A-47

SAN ANDRES STRUCTUREFUHRMAN-MASCHO FIELD

SAN ANDRES STRUCTUREFUHRMAN-MASCHO FIELD

2. Structurally, the field exhibits a local relief of about350 ft. Mapping of the McKnight shale, below, showsthat the early San Andres paleotopography bears norelationship to current structure.

STRATIGRAPHY AND FACIES

SUBREGIONAL DEVELOPMENT OF RESERVOIR POROSITY AT A MAJOR PERMIAN UNCONFORMITY:SAN ANDRES FORMATION, WEST TEXAS

1. The Fuhrman-Mascho field is located on the Central Basin Platform, an early Permian constructionalplatform. During San Andres deposition, the field area lay on a generally eastward-dipping carbonate ramp.

5. The reservoir section at Fuhrman-Mascho comprises an overall upward-shallowing succession of lower San Andres, upper San Andres, and Grayburgdeposits.

Grayburg Formation deposits are composed of restricted inner platform cyclesmade up of siltstone-rich bases and tidal-flat caps.

Upper San Andres (USA) rocks comprise a complex cyclic succession of innerplatform, shallow water subtidal carbonates (dominantly mud-dominatedpackstones), and cycle capping exposure tidal-flat facies.

Lower San Andres (LSA) rocks are dominantly outer ramp fusulinidwackestones with local capping peloid/ooid grain-dominated packstones andgrainstones.

SUBREGIONAL DEVELOPMENT OF RESERVOIR POROSITY AT A MAJOR PERMIAN UNCONFORMITY:SAN ANDRES FORMATION, WEST TEXAS

STRATIGRAPHY AND FACIES

BureauofEconomic

Geology

INTRODUCTIONINTRODUCTION

2

Z

1

A

3

D

4250

4700

ftft ft

4200

4150

4150

ft ft ft ft ftSGR

4700

4250

4592

4250

4600

D

4700

4250

4700

CGR

GR

4300

4700

4200

GR GR GR

4650

4600

1800 ft

2700 ft

3000 ft 2600 ft1300 ft

1700 ft

1900 ft1700 ft

GR GR GR GRN

NNN

N N N N N

Up

per

San

An

dre

s F

m.

Gu

adal

up

ian

HF

S 1

2-13

Gu

adal

up

ian

HF

S 1

-4L

ow

er S

an A

nd

res

Fm

.

Up

war

d-s

hal

low

ing

cyc

les

WFMU 124FMU 605FMU 12A FMU 211

WFMU 110 WFMU 109 FMU 806FMU 705FMU 607

Z

D

AGra

ybu

rg F

m. ft

QAc?? c

Stephen C. Ruppel,Bureau of Economic Geology,

The University of Texas, Austin, TX, 78713-8924

Most porosity development in carbonate reservoirs can be attributed in part orin total to diagenesis. This is especially true in Permian reservoirs of the PermianBasin, nearly all of which are dolomitized. Linking this diagenesis andassociated porosity to unconformities representing major falls in sea level,however, is commonly problematic using typical reservoir data sets. Newsubsurface data from the San Andres Formation, a major oil-producing reservoirin Texas and New Mexico, coupled with relationships previously defined fromequivalent outcrops, illustrate both the style and expression of such porositydevelopment.

Although the San Andres is characterized by an upward-shallowing successionof outer- to inner-ramp carbonate lithofacies in most platform settings, perviousstudies have demonstrated that the section is broken by a major unconformitythat represents a sea-level fall of at least 100 m and a hiatus of 0.5 to 1 my.

Both the evidence and the result of this sea-level fall event are clearly expressedin the San Andres reservoir at Fuhrman-Mascho field. Although cryptic in somecore sections, the hiatus is indicated by an abrupt shift from outer rampdeposits, composed of open marine fusulinid wackestones and packstones, toexposed tidal flat deposits. Porosity is developed in solution-enhanced verticalburrows below the unconformity. Although highly heterogeneous, the porosityin this burrowed zone reaches 15 m in thickness and extends for manykilometers. The widespread porosity development at this unconformity is apotential new target for both field exploitation and regional explorationoperations.

ABSTRACT

Stephen C. Ruppel,Bureau of Economic Geology,

The University of Texas, Austin, TX, 78713-8924

ABSTRACT

Guad. 12Guad. 13

North South

Algerita Escarpment Brokeoff Mts WesternEscarpment

DelawareMts

Leon. 7Leon. 8

Guad. 1Guad. 2

Guad. 3

Guad. 4

Guad. 4

Gu

ad. 5

-11

Guad. 5

Guad. 13

lowerSan Andres

upperSan Andres

0

1000 300

After Kerans and Ruppel (1994)0 10 km

5 10 mi

ft m

QAa1719c

Brushy Canyon Formation

Cutoff Formationdeep ramp mudstones

Lower Cherry Canyon Formation

Upper Victoria Peak Formationplatform carbonates

San Andres Formationplatform carbonates

Unconformity

Guad. 1- High-frequency sequence

LITHOSTRATIGRAPHICNOMENCLATURE

4. Lower San Andres carbonates comprise six Leonardian and Guadalupian high-frequency sequences (L7-L8, G1-G4),whereas the upper San Andres contains two high-frequency sequences (G12 and G13). During the long mid-SanAndres lowstand platform hiatus, deposition was limited to lowstand sandstones of high-frequency sequences G5- G11 (Brushy Canyon Formation).

STUDY AREA

PSL A-42

PSL A-43

UNIVERSITY LANDS

BLOCK 9

FUHRMAN-MASCHO FIELD

UNIVERSITY LANDS

BLOCK 10

EMMA FIELDDeeper WaterOuter Ramp

Cored well

Top ofMcKnight

-2100

Shallow WaterInner Ramp

QAc1875c C.I. 100 ft

-2200

-2000

-2000

LOWER SAN ANDRES PALEOTOPOGRAPHYFUHRMAN-MASCHO FIELD

0 10,000 ft

300 m0

LOWER SAN ANDRES PALEOTOPOGRAPHYFUHRMAN-MASCHO FIELD

PSL A-47PSL A-47

10

CYCLE STRATIGRAPHY AND FACIES ARCHITECTUREFuhrman-Mascho San Andres Field, Andrews County, Texas

6. Cross sections through the field demonstrate (1) long correlation lengths of Grayburg cycle-base siltstones, (2) poor continuity and predictability of upper San Andres cycles andcomponent facies, and (3) major facies offset marking the unconformity at the upper San Andres–lower San Andres boundary. Outer ramp fusulinid wackestones at the top of theLSA are sharply overlain by pisolitic, tidal-flat facies of the USA suggesting partial erosional truncation of the LSA.

Depth

100

0 0ft m

30QAc1877c

Ramp crest grain–dominated packstone–grainstone

Inner ramp–tidal flatmud-dominated facies

Peritidal tidal flatCore

LSA high porosity/permeability

Outer ramp fusulinidwackestone–packstone

Middle ramp peloidal–skeletal wackestone–packstone

Siltstone–sandstone

4400'

4500'

4300'

GGDP

PWS

Gamma ray (API) Neutron porosity (%)

30 -1020 0100

Depth(ft)

SGR

4300

4600

Oil

satu

rati

on

Per

mea

bili

ty

CGR

up

per

San

An

dre

slo

wer

San

An

dre

s 0 0

50 15ft m

10

Siltstone–sandstone

Mudstone

Peloidal wackestone–packstone

Peloidal grain-dominated packstone

Tidal flat

Fusulinid packstone

Gypsum

Cycle set

10

Gra

ybu

rg

Depth

QAc1876c

0

High-frequencycycle boundary

10

Northwest Southeast