PurposeTo construct a geologic and petrophysical model of the Panoma Field in sufficient detail to accurately represent the fine-scale vertical and lateral heterogeneities for accurate reservoir modeling of the entire field.

Abstract

The Panoma (Council Grove) Field in southwest Kansas lies stratigraphically subjacent to the more prolific Hugoton (Chase) Field, and has recovered 2.8 TCF of gas from approximately 2,600 wells across 1.7 million acres since its discovery in the early 1960's. Field-wide upscaling of lithofacies distribution for reservoir characterization has proven problematic in large heterogeneous reservoirs like the Panoma Field, but prediction tools, neural networks and the Excel add-in Kipling.xla, a non-parametric discriminant analysis tool, provide solutions to the facies prediction dilemma.

Panoma produces gas from the upper seven fourth-order sequences of the Permian Council Grove Group containing 50% nonmarine siliciclastics and 50% marine carbonates and siliciclastics. Lithofacies controlled petrophysical properties dictate gas saturations and discrimination of lithofacies reduces standard error in permeability prediction in marine carbonate facies by a factor of twelve. Nonmarine siliciclastic facies error was reduced by a factor of three. At low gas column heights, lithofacies discrimination can result in predicted saturation differences of 20-40% while differences at high gas column heights, near “irreducible”, are less than 10%.

Both a neural network and Kipling.xla were “trained” on data from eight wells including half-foot digital wireline log data and descriptions of two thousand feet of core utilizing a digital rock classification scheme. Both models were then used to predict lithofacies in non-cored wells based on their log attributes. Techniques employed in this study could be applied to other large and complex reservoirs where accurate representations of lithofacies heterogeneity in the 3D volume are key to realistic reservoir analysis. Kansas Hugoton Project

The Hugoton Project (http://www.kgs.ku.edu/Hugoton/index.html) is an Industry, University and Governmental funded consortium whose purpose is to develop technology and information to better understand the oil and gas resources of the Hugoton Embayment in Southwest Kansas. This paper is one of the outcomes of the five year project.

We wish to acknowledge members of the Hugoton Consortium that contributed data including Pioneer Natural Resources USA, Inc., BP, OXY USA, Inc., and Anadarko Petroleum Corp. We are grateful to those who served as technical advisors including Kevin Schepel, Louis Goldstein, and Randy Offenberger, Pioneer, and those that provided technical support including Bob Perry, Bill Tulp Jenna Anaya and Susan Leigh, Pioneer, Tim McGinnley, McGinnley and Associates, David Hamilton and Jeff Kiester, SCM, Inc., and Ken Dean and Mike Maroney, Kansas Geological Survey.

Statistically-based Lithofacies Predictions for 3-D Reservoir Modeling: Example from the Panoma (Council Grove) Field, Hugoton Embayment, Southwest Kansas

1 1 1 2 1 Martin K. Dubois , Alan P. Byrnes , Geoffrey C. Bohling , Shane C. Seals , and John H. Doveton(1) Kansas Geological Survey, University of Kansas,(2) Pioneer Natural Resources USA, Inc.

(AAPG 2003, Salt Lake City, Utah)

Http://www.kgs.ku.edu/PRS/publication/2003/ofr2003-30/index.html

(AAPG 2003, Salt Lake City, Utah)Http://www.kgs.ku.edu/PRS/publication/2003/ofr2003-30/index.html

Stratigraphy

Pe

rmia

n

Panoma

Bradshaw

Byerly

Hugoton

Greenwood

Sumner

Chase

CouncilGrove

Admire

Wabaunsee

ShawneePe

nn

sy

lva

nia

n

System Group FieldSeries

Wo

lfc

am

pia

nL

eo

na

rdia

nV

irg

ilia

n

Council Grove GroupFormation Member

FieldZone

SpeiserShale

FunstonLimestone

Blue RapidsShale

CrouseLimestone

Easly Creek Sh

Bader Limestone

MiddleburgLimestone

HooserShale

Eiss LS

Stearns Shale

Beattie Limestone

Morrill LsFlorence Sh

CottonwoodLimestone

EskridgeShale

NevaLimestoneGrenola

LimestoneSalem Point Sh

Burr LsLegion Sh

Sallyards Ls

NM Silt & Sd

NM Shly Silt

Mar Shale & Silt

Mudstone

Wackestone

Dolomite

Packestone

Grnst & PA Baf Newby 2-28R

Council Grove Stratigraphy

A1

B1

B2

B3

B4

B5

C

Solution: Use artificial intelligence to predict lithofacies in 500 wells and fill a 3D volume with lithofacies constrained porosity, permeability and gas saturations.

1. Identify and characterize key lithofacies and tie to core petrophysical properties. 2. Predict lithofacies for wells without cores using a neural net and electric log curves and marine-nonmarine indicator curve as predictor variables. Generate predicted lithofacies and probability curves. 3. Fill 3-D cellular volume with lithofacies and porosity using Petrel. 4. Add lithofacies-constrained permeability and gas saturations to cell properties with transform formulas and height above free water. 5. Export cellular model with porosity, permeability, and initial gas saturations to a reservoir simulator.

Statement of Problem: 1. No comprehensive geologic model for the Council Grove available. 2. Accurate reservoir model is critical for most efficient management of remaining resources in this large asset. 3. Lithofacies controlled petrophysical properties dictate gas saturations. 4. Accurate discrimination of lithofacies reduces error in predicted permeability and gas volume. 5. The Council Grove is a large, complex heterogeneous reservoir. 6. Field-wide upscaling of lithofacies distribution for reservoir characterize -ation and analysis of large heterogeneous reservoirs like the Panoma Field is impractical by traditional methods.

Permeability vs Porosity by Facies

0.00001

0.0001

0.001

0.01

0.1

1

10

100

1000

0 2 4 6 8 10 12 14 16 18 20 22 24

In situ Porosity (%)

In s

itu

Klin

ke

nb

erg

Pe

rme

ab

ilit

y (

md

)

1-NM Silt & Sand

2-NM Shaly Silt

3-Marine Sh & Silt

4-Mdst/Mdst-Wkst

5-Wkst/Wkst-Pkst

6-Sucrosic Dol

7-Pkst/Pkst-Grnst

8-Grnst/PhAlg Baff

Capillary Pressure Curves by Facies(Porosity = 10%)

10

100

1000

0 10 20 30 40 50 60 70 80 90 100Water Saturation (%)

Ga

s-B

rin

e H

eig

ht

Ab

ov

e F

ree

Wa

ter

(ft)

1-NM Silt&Sand

2-NM Shaly Silt

3-Marine Sh & Silt

4-Mdst/Mdst-Wkst

5-Wkst/Wkst-Pkst

6-Sucrosic Dol

7-Pkst/Pkst-Grnst

8-Grnst/Grnst-PhAlg Baff

Capillary Pressure Curves by Facies(Porosity = 7%)

10

100

1000

0 10 20 30 40 50 60 70 80 90 100

Water Saturation (%)

Ga

s-B

rin

e H

eig

ht

Ab

ov

e F

ree

Wa

ter

(ft)

1-NM Silt & Sand

2-NM Shaly Silt

3-Marine Sh & Silt

4-Mdst/Mdst-Wkst

5-Wkst/Wkst-Pkst

6-Sucrosic Dol

7-Pkst/Pkst-Grnst

8-Grnst/PhAlg Baff

Council Grove facies identification is important to reservoir characterization because petrophysical properties vary between facies. At porosities > 6% permeability in grainstone/bafflestones can be 30X greater than mudstones and >100X greater than marine siltstones of similar porosity. Differences in permeabilities between nonmarine silt/sand-stones and shaly siltstones range from 3.3X at 12% porosity to 7X at 18%.

Capillary pressures and corresponding watersaturations also vary between facies. For example, at 7% porosity (which represents >50% of all Mstn/Wkstn) at200 ft above free water Mudstones are 100% water saturated while grainstones exhibit water saturations of ~40%. Differences in water saturations between facies increase with decreasing porosity and decreasing height above free water.

Lithofacies, Sequences, Depositional Environments

"Lumped" LithofaciesCouncil Grove A1- B5

Grain

Support &

Dolomite

20%Mud

Support

30%

Non-

marine

45%

Lithofacies DistributionCouncil Grove, Panoma Field

26%

23%12%

4%

8%7%16%

4%

NM Silt & Sd

NM Shly Silt

Mar Shale & Silt

Mudstone

Wackestone

Dolomite

Packestone

Grnst & PA Baf

(For A1 - B5)

A1-B5 Pay Facies (L6,7,8)(Sum of Net / Sum of Gross)

468 “LAS” Wells

Shoa

l

Tidal F

lat

Tida

l

Flat

Carb

onat

e

Dom

inat

ed

Shelf

Silic

icla

stic

Dom

inat

ed S

helf

Coas

tal P

lain

Lago

on

Shoa

l

Phyl

oid

Alga

l

Idealized Depositional Model

(Modified after Reservoirs, Inc.)

Lithofacies and Depositional Environments

In the Panoma Field of southwest Kansas the Council Grove Group comprises seven fourth-order marine-nonmarine sequences. Through the detailed study of ten widely distributed and lengthy cores eight major lithofacies were identified and characterized (see Panel 2).

During Council Grove deposition, the Panoma Field area was situated on a broad shallow shelf or ramp that dipped gently southward into the Anadarko basin in Oklahoma. The geometry of the shelf was conducive for broad, parallel depositional environments and associated lithofacies belts. In response to cyclical sea level fluctuations, lithofacies belts migrated across the shelf resulting in a predictable vertical succession of the eight major lithofacies.

Beaty

Newby

Alexander

Cores Available

Shankle

Luke

Shrimplin

Kimzey

Stuart

(Key wells are named)

Easly Creek Sh

Middleburg LS

Hooser Sh

Eiss Ls

Ba

de

r L

s

Co

re P

ho

tos Sequence Boundary

Flooding Surface

Sequence Boundary

Flooding Surface

NM Silt & Sd

NM Shly Silt

Mar Shale & Silt

Mudstone

Wackestone

Dolomite

Packestone

Grnst & PA Baf

Core from Middleburg (B2 LM)Strat X-Sections

Northwest to southeast cross sections illustrate the large-scale lithofacies and depositional relationships in the Panoma Field. The updip limit to the Panoma coincides with thinned marine carbonate intervals and their reciprocally thicker nonmarine silts and shaly silts. The smaller scale cross section of the same wells shows the 8 lithofacies using Petrel's interpretive colorfill. It illustrates some major lateral and vertical facies relationships but is not to be considered a true representation of the finer geometries.

Seven SequencesThe Council Grove Group is comprised of seven fourth-order marine-nonmarine sequences bounded by unconformities on exposed carbonate surfaces. A typical vertical succession, beginning at the exposed carbonate surface, are primarily wind blown silts, very fine sands and clay rich silts with paleosols. Above a flooding surface are generally thin, shallow water carbonates with grain-supported textures deposited during the initial, shallow water portion of the flooding event. These are overlain by deeper water dark marine siltstones and silty carbonate mud- and wackestones which are, in turn, overlain by “cleaner” mud- and wackestones deposited in shallower water. With progressive shallowing these are overlain by either packstones and grainstones, interpreted to indicate increased wave or tidal agitation; quiet water, lagoonal, mudstones and wackestones; or silty dolomites and dolomites, where there was little or no wave agitation. Fenestral and laminated tidal flat carbonates are also common near the top of the carbonate interval. Exposure is evidenced by well-developed calcretes, root molds, and other indicators. Higher frequency cycles are evident in the Funston and Neva, in particular.

StatisticsIInitial Prod 19682002 Prod 67 BCFCum. Prod 2.88 TCF gasWell count 2600Per well avg. 1.1 BCF to dateArea 1.7 million acres

(1 well per sect)Top of pay 2500-3200 feet

(+800 to 100)Current SIP ~60#OriginaSIPl ~480#

Setting and History

PANOMA FIELD GAS PRODUCTION

0

20

40

60

80

100

120

140

160

1965 1975 1985 1995 2005

An

nu

al

Pro

d.

(BC

F/Y

)

0

500

1,000

1,500

2,000

2,500

3,000

3,500C

um

ula

tive

Pro

d.

(BC

F)

0

100

200

300

400

500

600

700

800

900

1,000

1930 1940 1950 1960 1970 1980 1990 2000

An

nu

al P

rod

uc

tio

n (

BC

F)

Panoma

Hugoton Area-Panoma

Non-Hugoton Gas

Kansas Annual Gas Production

Bra

dsh

aw

Pan

om

a

Hu

go

ton

Gre

en

wo

od

+1000 +

500

O (S

L)

-500

Council Grove StructureCI = 100 feet

Modified after Pippin (1985)

Generalized Field X-Section

Panoma

Hugoton

Cumulative Gas Per Well(Council Grove)

KANSAS

CentralKansasUplift

0

0 100 K

100 M

NemahaAnticline

SalinaBasin

CherokeeBasin

Forest CityBasin

SedgwickBasinHugoton

Embayment

Keyes Dome

The Panoma Field (2.9 TCF gas) produces from Permian Council Grove Group marine carbonates and nonmarine silicilastics in the Hugoton embayment of the Anadarko Basin. It and the Hugoton Field, which has produced from the Chase Group since 1928, the top of which is 300 feet shallower have combined to produce 27 TCF gas, making it the largest gas producing area in North America. Both fields are stratigraphic traps with their updip west and northwest limits nearly coincident. Maximum recoveries in the Panoma are attained west of center of the field. Deeper production includes oil and gas from Pennsylvanian Lansing-Kansas City, Marmaton, and Morrow and the Mississippian.

Maps and cross sections in this panel were created In geoPLUS Petra with an academic license.

General Panoma Field

Geology

A1-B5 Thickness

8000 Wells

Gross Nonmarine Thickness

536 “LAS” Wells

Gross Marine Thickness

536 “LAS” Wells

Maps of the A1SH (top Council Grove) through the B5LM (base Cottonwood)

The most striking large-scale geometry feature of the Panoma reservoir is the reciprocal relationship between nonmarine and marine interval thickness. Though the total thickness of the Council Grove (A1-B5) in most of the study area varies less than 50 feet (from 200-250 feet), the summed nonmarine and marine intervals each vary 120 feet (from 50-170 feet) and their respective summed thicknesses are reciprocal. Thick nonmarine shale and silt dominates the northwest side of the study area while marine carbonates dominate to the southeast.

Panoma

A1 LM Funston

B1 LM Crouse

B2 LM Middleburg

B3 LM EisB4 LM MorrillB5 LM Cottonwood

C LM NevaNot to Scale

Stratigraphic Cross SectionDatum: Top of Council Grove

20

0 F

ee

t

60

0 M

ete

rs

Pa

no

ma

Fie

ld

Up

dip

Lim

it

Non Marine

Mdst, Wkst & Shale

Pkst, Grnst & Dol.

NM Silt & Sd

NM Shly Silt

Mar Shale & Silt

Mudstone

Wackestone

Dolomite

Packestone

Grnst & PA Baf

Lithofacies are those predicted by neural net models (see Panel 3) in wells without triangles around the well symbols. Lithofacies by core description are shown in wells with triangles which are two of the eight ‘keystone wells.”

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