stephen c. ruppel, san andres formation, west texas · 4. lower san andres carbonates comprise six...
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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