Sligo Model

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Stratigraphic Framework and New Exploration Concepts for the Lower Cretaceous Shelf Margin Carbonates of Texas* By Paul M. (Mitch) Harris 1 Search and Discovery Article #40303 (2008) Posted September 3, 2008 *Adapted from 2000-2001 AAPG International Distinguished Lecture 1 Chevron Petroleum Technology Company, Houston, TX; currently ETC, Chevron, San Ramon, CA, USA ([email protected] ) Abstract Stratigraphic studies, focusing on the Lower Cretaceous Edwards and Sligo margins in East-central Texas, suggest new exploration opportunities. One is based on an extension of the favorable stratigraphy of the Edwards beyond the commonly recognized shelf margin; and another on recognizing that the Sligo margin underwent a major period of exposure resulting in deposition of downslope debris wedges. These examples show how new exploration ideas can be developed in mature areas when new tools and approaches are utilized. The Edwards - An Underdrilled Opportunity Analysis of well cuttings and core, coupled with detailed seismic correlation, confirms that the Edwards margin consists of both grainstone and reef facies and shows that both sets of facies repeat themselves several times within the Edwards as the margin prograded. The Edwards margin prograded southeastward >5 km beyond the Sligo margin placing prospective backreef and reef grainstones far seaward of the commonly recognized margin. In essence, there are equivalent facies to those of the Word field complex, a mature Edwards gas field producing at a depth of approximately 3962 m, downdip of the field but the facies lack the underpinning of the Sligo margin for structural drape. The extent of this “opportunity fairway” within Lavaca County alone is over 4.8 km in width and 40 km in length. 3-D seismic and a corresponding geologic cross section show the progradational nature of the Edwards in detail. Three Edwards sequences defined by four key reflectors on the 3-D data occur within one sequence on the 2-D seismic. Reflector 1, which is a high- amplitude event downdip that diminishes in strength updip, occurs at the top of an interval of deeper water argillaceous wackestones (Upper Tamaulipas). Reflector 1 is immediately overlain by a prograding reef/bank complex and distal slope wackestones of the

Transcript of Sligo Model

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Stratigraphic Framework and New Exploration Concepts for the Lower Cretaceous Shelf Margin Carbonates of Texas*

By Paul M. (Mitch) Harris1

Search and Discovery Article #40303 (2008)

Posted September 3, 2008

*Adapted from 2000-2001 AAPG International Distinguished Lecture 1Chevron Petroleum Technology Company, Houston, TX; currently ETC, Chevron, San Ramon, CA, USA ([email protected])

Abstract

Stratigraphic studies, focusing on the Lower Cretaceous Edwards and Sligo margins in East-central Texas, suggest new exploration opportunities. One is based on an extension of the favorable stratigraphy of the Edwards beyond the commonly recognized shelf margin; and another on recognizing that the Sligo margin underwent a major period of exposure resulting in deposition of downslope debris wedges. These examples show how new exploration ideas can be developed in mature areas when new tools and approaches are utilized. The Edwards - An Underdrilled Opportunity Analysis of well cuttings and core, coupled with detailed seismic correlation, confirms that the Edwards margin consists of both grainstone and reef facies and shows that both sets of facies repeat themselves several times within the Edwards as the margin prograded. The Edwards margin prograded southeastward >5 km beyond the Sligo margin placing prospective backreef and reef grainstones far seaward of the commonly recognized margin. In essence, there are equivalent facies to those of the Word field complex, a mature Edwards gas field producing at a depth of approximately 3962 m, downdip of the field but the facies lack the underpinning of the Sligo margin for structural drape. The extent of this “opportunity fairway” within Lavaca County alone is over 4.8 km in width and 40 km in length. 3-D seismic and a corresponding geologic cross section show the progradational nature of the Edwards in detail. Three Edwards sequences defined by four key reflectors on the 3-D data occur within one sequence on the 2-D seismic. Reflector 1, which is a high-amplitude event downdip that diminishes in strength updip, occurs at the top of an interval of deeper water argillaceous wackestones (Upper Tamaulipas). Reflector 1 is immediately overlain by a prograding reef/bank complex and distal slope wackestones of the

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Edwards margin as seen in cores and cuttings. Reflector 2 is a weak event that ties lagoonal packstone/grainstones to a reef and bank complex and eventually forereef and slope deposits. Reflectors 3 and 4 tie backreef wackestone/packstones to reef and backreef grainstones. It seems clear that the "top Edwards" interval between reflectors 3 and 4 represents a progradational package whose ultimate culmination is even seaward of the study area. The Sligo Forereef – An Untested Opportunity A 3-D seismic line illustrates a major sequence boundary in the Sligo margin and several events on the seaward side of the margin that display onlap and downlap reflector terminations. These events exhibit the proper architecture to comprise part of a downslope debris wedge in excess of 300 m thick. Although this Sligo forereef and slope play is regional in extent throughout the northern rim of the Gulf of Mexico, the opportunity has yet to be tested. The existence of a Sligo downslope wedge between the sequence boundary and the overlying Pearsall shale does not guarantee the presence of coarse grained material. It is likely the lowstand created a period of instability, resulting in coarse breccia and grainstone transported further downslope in the form of debris flows and sediment gravity flows. During the subsequent transgression and relative highstand, the Sligo shelf margin initially kept up with sea level rise and continued to contribute grainstone debris downslope. Rapid deposition of the downslope carbonates may have helped to preserve primary porosity by limiting the amount of marine cementation. Data from reservoir analogs confirm that such downslope carbonates can retain reservoir-quality porosity; e.g., Poza Rica field from east-central Mexico. Facies variation and slump faulting on the foreslope creates the potential for trapping and juxtaposition to deep-water carbonates sets up the source and migration pathway. Eventually, the Sligo shelf margin was flooded by a major transgression represented by the Pearsall, which would provide a top seal.

Acknowledgments I am grateful to the following coworkers for their collaboration: Terry W. Belsher, James M. Medlin (retired), John L. Stubbs, and Robert P. Wright, Chevron U.S.A. Production Company, Houston, TX; Dale A. Fritz, Devon Energy, Oklahoma City, OK. 2D seismic data were provided by Seismic Exchange Inc, and 3D seismic data were provided by CGG Americas Inc.

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STRATIGRAPHIC FRAMEWORK AND STRATIGRAPHIC FRAMEWORK AND NEW EXPLORATION CONCEPTSNEW EXPLORATION CONCEPTS

LOWER CRETACEOUS SHELF MARGINLOWER CRETACEOUS SHELF MARGINCARBONATES OF TEXASCARBONATES OF TEXAS

AAPG International Distinguished Lecture TourAAPG International Distinguished Lecture Tour

Paul M. (Mitch) HarrisPaul M. (Mitch) HarrisChevron Petroleum Technology CompanyChevron Petroleum Technology Company

Houston, Texas U.S.A.Houston, Texas U.S.A.

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EXPLORATION CONCEPTSEXPLORATION CONCEPTSLOWER CRETACEOUS SHELF MARGINLOWER CRETACEOUS SHELF MARGIN

CARBONATES OF TEXASCARBONATES OF TEXAS

Paul M. (Mitch) HarrisPaul M. (Mitch) HarrisChevron Petroleum Technology CompanyChevron Petroleum Technology Company

Houston, Texas U.S.A.Houston, Texas U.S.A.

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OUTLINE OF TALKOUTLINE OF TALK

•• Regional and Stratigraphic SettingRegional and Stratigraphic Setting

•• Edwards PlayEdwards Play

•• SligoSligo Analog and PlayAnalog and Play

•• SummarySummary

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OUTLINE OF TALKOUTLINE OF TALK

•• REGIONAL AND STRATIGRAPHIC SETTINGREGIONAL AND STRATIGRAPHIC SETTING

•• EDWARDS PLAYEDWARDS PLAY

•• SLIGO ANALOG AND PLAYSLIGO ANALOG AND PLAY

•• SUMMARYSUMMARY

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G ulf o f M ex ic o

POZA RICA TREND

GOLDEN LANEPLATFORM

VALLESSAN LUIS P OTOSI

PLATFORM

MAVERICKBASIN

EAST TEXASBASIN MISSIS SIPPI

SALT BASINSAN MARCOS

ARCH

LOWER CRETACEOUSMARGIN

EDWARDS MARGINSLIGO MARGIN

REGIONAL MAPREGIONAL MAP

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TAYLORAUSTIN

EDWARDSPEARSALL

SLIGO

HOSSTON

1 MILE

GOLDEN LANETYPE MARGIN

POZA RICA TYPE WEDGES

WORD FIELDACTUAL

EDWARDSMARGIN

PUBLISHEDEDWARDS

MARGIN

SLIGO MARGIN

TAYLOR

AUSTINEDWARDS

PEARSALLSALT

PLAY TYPESPLAY TYPES

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Gulf of Mexico

STUDY AREA

EDWARDS SHELF TREND

SLIGO SHELF TREND

DETAILED STUDY AREADETAILED STUDY AREA

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Louann

HaynesvilleFm

SmackoverFm

BossierShale

Cotton ValleyGp

Hosston Fm

Sligo

Atascosa

Midway

Navarro

Taylor

Austin Chalk

Eagle Ford

Georgetown

Fredericksburg

UpperGlen Rose

LowerGlen Rose

Knowles

Buckner

BudaWoodbine

Upper SligoJames

Pearsall

160

150

140

130

120

110

100

90

80

70

60

SLRise Fall

CompositeCurve Shelfward Basinward

2nd-OrderSuper

Sequence

LST

TST

HST

TST

HST

TSTSMW

HST

SMWTST

HST

(MFS)TST

158.5

144

128.5

112

84

(MFS)

(MFS)

98

GULF COAST STRATIGRAPHYGULF COAST STRATIGRAPHY

EDWARDS EDWARDS PROGRADINGPROGRADING

SHELF MARGINSHELF MARGINPLAYPLAY

ALBIANALBIAN

APTIANAPTIANBARREMIANBARREMIANHAUTERIVIANHAUTERIVIANVALANGINIANVALANGINIAN

TURONIANTURONIANCENOMANIANCENOMANIAN

BERRIASIANBERRIASIANTITHONIANTITHONIAN

KIMMERIDGANKIMMERIDGAN

OXFORDIANOXFORDIAN

CALLOVIANCALLOVIAN

CONIACIANCONIACIANSANTONIANSANTONIAN

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LAVACA COUNTYTEXAS

N

PUBLISHEDEDWARDS / SLIGO

MARGIN

TOP EDWARDS STRUCTURETOP EDWARDS STRUCTURE

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DATA BY SEISMIC EXCHANGE INC.

TOP CRETACEOUSI

S

S

COTTON VALLEY

SLIGO PEARSALL

GLEN ROSE EDWARDS

2D SEISMIC FRAMEWORK2D SEISMIC FRAMEWORK

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2D SEISMIC FRAMEWORK2D SEISMIC FRAMEWORK

SLIGOSLIGO

EDWARDSEDWARDS

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SEISMIC INTERPRETATIONSEISMIC INTERPRETATION

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3382'

NW SE

2000 2000

2500 2500

3000 3000

3500 3500

4000 4000

Seismic Provided by CGG AMERICAS INC.

EDWARDS 3D SEISMICEDWARDS 3D SEISMIC

EDWARDSEDWARDS

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WORD FIELD DEPOSITIONAL MODELWORD FIELD DEPOSITIONAL MODEL

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EDWARDSEDWARDSREEF FACIESREEF FACIES

RUDISTSRUDISTS

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EDWARDSEDWARDSREEF FACIESREEF FACIES

RUDISTSRUDISTS

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EDWARDSEDWARDSGRAINSTONEGRAINSTONE

FACIESFACIESRUDIST DEBRISRUDIST DEBRIS

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N

0' 4000' 8000'

#1 ZARUBAEDWS -14,063'

#1 COBYEDWS -13,927'

Seismic Provided by CGG AMERICAS INC.

PUBLISHEDEDWARDSMARGIN

3D SEISMIC LOCATION3D SEISMIC LOCATION

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14000

14500

15000

15500

16000

BACK REEF GRAINSTONE

PROXIMAL SLOPE WACKESTONE

AUSTIN CHALK

EAGLE FORDBUDAEDWARDS

REEF GRAINSTONE

FORE REEF PACKSTONE

DISTAL SLOPE WACKESTONE

DEEP SHELFARGILLACEOUS WACKESTONE

KEY EDWARDS WELLKEY EDWARDS WELL

FACIES FROM FACIES FROM CUTTINGS DESCRIPTIONCUTTINGS DESCRIPTION

PROGRADATIONALPROGRADATIONALMOTIFMOTIF

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2.5

3.0

3.5

CHEVRONCOBY #1

EXXONZARUBA #1

MOBILKAHANEK #1(PROJECTED 13 MILES ALONG STRIKE)

SLIGO DEBRIS

HST

TS T

Reef TSTHST

HSTTS T

TOP EDWARDS

HST

1

234

14,000'

16,000'

Seismic Provided by CGG AMERICAS INC.

EDWARDS STRATAL GEOMETRIESEDWARDS STRATAL GEOMETRIES

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EDWARDS FACIES ARCHITECTUREEDWARDS FACIES ARCHITECTURE

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Refined Stratigraphic and Facies Framework Refined Stratigraphic and Facies Framework Indicates Exploration OpportunitiesIndicates Exploration Opportunities

EDWARDS PLAY SUMMARYEDWARDS PLAY SUMMARY

Well and Seismic Control Extend Margin Well and Seismic Control Extend Margin SeawardSeaward

EdwardsEdwards is Largely is Largely StratigraphicallyStratigraphically TrappedTrapped

Porosity Likely Enhanced by Dissolution Along Porosity Likely Enhanced by Dissolution Along FracturesFractures

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LAVACA COUNTYTEXAS

N

OPPORTUNITYFAIRWAY

PUBLISHEDEDWARDS / SLIGO

MARGIN

ACTUALEDWARDSMARGIN

EDWARDS OPPORTUNITIESEDWARDS OPPORTUNITIES

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G ulf o f M ex ic o

POZA RICA TREND

GOLDEN LANEPLATFORM

VALLESSAN LUIS P OTOSI

PLATFORM

MAVERICKBASIN

EAST TEXASBASIN MISSIS SIPPI

SALT BASINSAN MARCOS

ARCH

LOWER CRETACEOUSMARGIN

EDWARDS MARGINSLIGO MARGIN

REGIONAL MAPREGIONAL MAP

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Louann

HaynesvilleFm

SmackoverFm

BossierShale

Cotton ValleyGp

Hosston Fm

Sligo

Atascosa

Midway

Navarro

Taylor

Austin Chalk

Eagle Ford

Georgetown

Fredericksburg

UpperGlen Rose

LowerGlen Rose

Knowles

Buckner

BudaWoodbine

Upper SligoJames

Pearsall

160

150

140

130

120

110

100

90

80

70

60

SLRise Fall

CompositeCurve Shelfward Basinward

2nd-OrderSuper

Sequence

LST

TST

HST

TST

HST

TSTSMW

HST

SMWTST

HST

(MFS)TST

158.5

144

128.5

112

84

(MFS)

(MFS)

98

GULF COAST STRATIGRAPHYGULF COAST STRATIGRAPHY

SLIGOSLIGODOWNSLOPEDOWNSLOPE

DEBRISDEBRISPLAYPLAY

ALBIANALBIAN

APTIANAPTIANBARREMIANBARREMIANHAUTERIVIANHAUTERIVIANVALANGINIANVALANGINIAN

TURONIANTURONIANCENOMANIANCENOMANIAN

BERRIASIANBERRIASIANTITHONIANTITHONIAN

KIMMERIDGANKIMMERIDGAN

OXFORDIANOXFORDIAN

CALLOVIANCALLOVIAN

CONIACIANCONIACIANSANTONIANSANTONIAN

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.

Sierra Madre Oriental

Sierra de El AbraS.L.

WEST EAST

Gulf of Mexico

Golden LanePlatform

After Yurew ic 1997

POZA RICA

Cret

POZA RICA CROSS SECTIONPOZA RICA CROSS SECTION

z,

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2D SEISMIC FRAMEWORK2D SEISMIC FRAMEWORK

SLIGOSLIGO

EDWARDSEDWARDS

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SEISMIC INTERPRETATIONSEISMIC INTERPRETATION

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POZA RICA ANALOGPOZA RICA ANALOG

POZA RICAPOZA RICA

POZA RICA

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DOWNSLOPE BRECCIA ON OUTCROPDOWNSLOPE BRECCIA ON OUTCROP

Graded BrecciaGraded Breccia

Pelagic Pelagic MudstoneMudstone

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DOWNSLOPE BRECCIA IN COREDOWNSLOPE BRECCIA IN CORE

Rudist Rudist GrainstoneGrainstone

ClastClast

WackestoneWackestoneClastClast

PelagicPelagicMudstoneMudstone

MatrixMatrix

SuturedSuturedContactsContacts

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GRAINSTONEGRAINSTONEDEBRISDEBRISIN COREIN CORE

RudistRudistFragmentsFragments

Interparticle Porosity of 2%Interparticle Porosity of 2%Moldic Porosity of 13.5%Moldic Porosity of 13.5%

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SLIGO SEQUENCE BOUNDARYSLIGO SEQUENCE BOUNDARY

HIGHSTANDHIGHSTANDPLATFORMPLATFORM

TRANSGRESSIVETRANSGRESSIVEPLATFORMPLATFORM

SBSB

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SLIGO SEQUENCE BOUNDARYSLIGO SEQUENCE BOUNDARY

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3382'

NW SE

2000 2000

2500 2500

3000 3000

3500 3500

4000 4000

Seismic Provided by CGG AMERICAS INC.

SLIGO 3D SEISMICSLIGO 3D SEISMIC

SLIGOSLIGO

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A A'

TAYLORAUSTIN

EDWARDSPEARSALL

SLIGO

HOSSTON

1 MILE

GOLDEN LANETYPE MARGIN

POZA RICA TYPE WEDGES

SLIGO MARGIN

TAYLOR

AUSTINEDWARDS

PEARSALLSALT

.

SLIGO PLAY TYPESLIGO PLAY TYPE

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PozaPoza Rica Analog for Rica Analog for SligoSligo Downslope Debris Downslope Debris PlayPlay

HighHigh--Resolution Sequence Framework Critical Resolution Sequence Framework Critical for Defining Reservoir and Trapfor Defining Reservoir and Trap

3d Seismic Essential for Stratigraphic Play 3d Seismic Essential for Stratigraphic Play DelineationDelineation

SLIGO PLAY SUMMARYSLIGO PLAY SUMMARY

High Risk but Potentially High RewardHigh Risk but Potentially High Reward

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Gulf of Mexico

SLIGO SHELF TREND

OPPORTUNITY FAIRWAY

SLIGO OPPORTUNITIESSLIGO OPPORTUNITIES

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SUMMARY POINTSSUMMARY POINTS

Although in a Mature Area, the Edwards and Although in a Mature Area, the Edwards and SligoSligoCarbonates Discussed Here are Far From Fully Carbonates Discussed Here are Far From Fully Exploited.Exploited.

3d Seismic, a Sequence Stratigraphic Framework, and 3d Seismic, a Sequence Stratigraphic Framework, and Reservoir Analogs Have Led to New Exploration Play Reservoir Analogs Have Led to New Exploration Play Concepts and Viable Opportunities.Concepts and Viable Opportunities.