Brian J. Cardott
Oklahoma Geological Survey
Application of Organic Petrology to Shale Oil and Gas Potential of the Woodford Shale, Oklahoma, USA
TSOP Annual MeetingAugust 1, 2011Three Basic Factors Necessary for a Successful Gas Shale Play
Hydrocarbon Source Rock: Organic Matter TYPE, QUANTITY, AND THERMAL MATURITY.
Mineralogy:quartz and carbonate vs. clays. Mineralogy and rock fabric influence porosity and mechanical strength (brittleness vs. ductile)
Stress:rock is difficult to break and fractures may close in high stress; low stress regions result in better stimulation.
Modified from Norton and Tushingham, 2011)Criteria from U.S. Energy Information Administration “World Shale Gas Resources: An Initial Assessment of 14 Regions Outside the United States”
Higher thermal maturity shales may contain nanopores that contribute to additional porosity in the shale matrix. [What is the effect of thermal maturity and OM type on porosity?]
Marine shales [e.g., Type II Kerogen] tend to have less clay and more brittle minerals (e.g., quartz, feldspar, carbonate) that respond well to hydraulic fracturing.
Non-marine shales [e.g., Type I Kerogen] tend to have more clay, are more ductile, and absorb frac energy.„Magnificent Seven‟ Gas Shale Basins of the U.S. and CanadaUNITED STATESCANADA
Woodford (Late Devonian-Early Mississippian)
From Kuuskraa, 2011All gas shales have marine Type II Kerogen bulk compositionComer (1992)
Woodford ShaleWoodford Shale Plays
Geologic provinces from Northcutt and Campbell, 1995
OilBiogenic Methane1,725 Woodford Shale Wells(2004-2011)1,366359Importance of thermal maturity (by vitrinite reflectance) on the Woodford Shale oil and gas plays.VRo ValuesMaturity
0.55-1.15% Oil Window (peak
oil at 0.90%VRo)
>1.40% Dry-Gas WindowFrom Jarvie and others, 2005
Guidelines for the Barnett Shale (Based on Rock-Eval Pyrolysis)Distribution of 112Woodford Shale samples with vitrinite-reflectance data (n ≥20; whole-rock pellets)Eastern OklahomaCardott, in preparationMISSISSIPPIAN& OLDEROUTCROPAREACHOCTAW FAULT11432211.310.560.790.590.782.190.640.6421.732.091.371.791.981.870.571.231.050.860.7410.723.322.690.522.940.580.50.550.570.80.830.7184.108.40.206.230.792.530.570.560.61.690.821.883.462.42.442.483.4220.127.116.113.444.856.364.760.590.560.540.490.670.571.07.518.104.22.1680.50.562.813.472.252.261.882.552.90.520.640.620.631.881.892.522.510.510.511.151.661.622.850.940.980.945.281.612.01.582.292.551.121.452.311.031.831.560.863.0412.522.214.171.1243.190.591.91PETRA 10/6/2009 3:10:12 PM
Isoreflectance Map of the Woodford Shale in Eastern Oklahoma (Updated October 2009)
Cardott, in preparation
Map prepared by R. Vance Hall using PetraMississippian and Older Outcrop Area (different than Ozark Uplift Province boundary)-5,000-15,000-10,000342
Woodford Shale Structure& VitriniteIsoreflectanceMapArkoma Basin Initial PotentialMostly Vertical (shallower/thinner)Mostly HorizontalWoodford Oil/Condensate/Gas ProductionCaveat
Gasproduction is reported by the Oklahoma Corporation Commission by WELL.
Oil/condensateproduction is reported by the Oklahoma Tax Commission by LEASE [production by well is only on single-well leases]
(Production data supplied by PI/Dwights LLC, © 2011, IHS Energy Group)Woodford Shale Oil/Condensate/Gas Production (2004-2011)
Condensate based on 54.4 API DEGProduction in first few months is interpreted as flowback from oil-based drilling mud(1) Newfield 3H-36 Genevieve (36-6N-11E; Hughes Co.; IP 2,118 Mcfd)Liquids production only in first few months interpreted as flowback@ 2.05%VRoIntermittent liquids production in first few months interpreted as oil-based drilling mud flowback(2) Cimarex 3-34H Hall(34-3N-11E; Coal Co.; IP 1,740 Mcfd)@ 2.05%VRoWoodford Shale-Only Condensate Wells Excluding Early Month Spikes3
4(3) St. Mary Land & Exploration 3-14 Marvin(14-1N-10E; Coal Co.; IP 3,125 Mcfd)Example of Woodford condensate produced later in well‟s life1.67%VRo(4) Antero 30-1H Harris
(30-1S-11E; Coal Co.; IP 1,334 Mcfd)
Spikes in production may be from intermittent trucking
@ 1.6%VRoAnadarko BasinWoodford Shale Isoreflectance Map based on 81wells (Cardott, 1989)Anadarko Basin Initial PotentialUSING THE SAME CRITERIA AS FOR THE ARKOMA BASIN TO EXCLUDEWELLS WITH LOW AMOUNTS OF EARLY LIQUID PRODUCTIONAnadarko Basin Produced LiquidsWoodford Shale VRo on StructureWoodford Shale IPs on StructureThe Bakken Shale (Late Devonian-Early Mississippian; North Dakota & Montana) is the analog for shale oil plays. However, the reservoir of the Bakken is a permeable, non-shale middle member.
Other formations considered shale oil plays (mostly carbonates) are the Eagle Ford Shale (Late Cretaceous; Texas) and Niobrara Shale (Late Cretaceous; Rocky Mountains).
“The preferred rock type for a shale-oil play is a hybrid—that is, a formation with a good mix of non-shale lithologies, particularly carbonates” (Darbonne, 2011)
Shale Oil PlaysWoodford Production on Structure Oil production from silica-rich rock is from natural fracturesCherokee Platform Initial Potential on Isoreflectance MapCherokee Platform Production on Isoreflectance Map
Some Biogenic Methane (note outcrop)Woodford-Only Production
1,475 wells with production data; excludes 55 OWWOCumulative: 932 Bcf, 3,701,330 BoOther useful petrographic thermal maturity indicators:
Fluorescence color of telalginite [qualitative indicator in oil window] (green, greenish-yellow, yellow, orange, extinguished)
Bitumen reflectance“The primary mechanism of gas production from shalesis the fracture networkin the reservoir. Gas residing in the very tight matrix system is forced to flow into the fracture network, first through chemical desorptionand then through diffusion, to travel to the matrix/fracture interface.” (Biswas, 2011)What is the potential for gas storage and diffusion within the organic network in shale?Importance of Bitumen to Gas-Shale Plays
Thermal Maturity Indicator
Porous sites for gas storage and migrationBitumen is defined as organic matter that is soluble in organic solvents (e.g., carbon disulphide). There are many names for this type of organic matter:BitumenSolid BitumenMigrabitumenSolid HydrocarbonAsphaltiteAsphaltic PyrobitumenGeneric Bitumen ClassificationHunt (1979)Genetic Bitumen Classification
Pre-Oil Solid Bitumen: early-generation products of rich source rocks, probably extruded from their sources as a very viscous fluid, and migrated the minimum distance necessary to reach fractures and voids in the rock. [Kerogen Bitumen Oil]
Post-Oil Solid Bitumen: products of the alteration of a once-liquid crude oil, generated and migrated from a conventional oil source rock, and subsequently degraded. [solid residue of primary oil migration]
Curiale (1986)Use of pre-oil solid bitumen as thermal maturity indicatorfollowing “solid hydrocarbon” reflectance to vitrinite reflectance equivalent regression equation of Landis and Castaño (1994)VRE = (BRo + 0.41)/1.09Homogenous formGranular form
Two Common Pre-Oil BitumenOptical Forms Based on Landis and Castaño (1994)
[regression equation is based on homogenous form]
OPL 1076500XFormation of Pre-Oil Bitumen from Tasmanites200X(OPL 1386; @ 0.67% Ro)(OPL 1395; 0.62% Ro)200X [field width is 320 microns]Proposed Post-Oil Bitumen NetworkClassification (@ 500X)Speckled WispyConnectedOPL 1372OPL 1366
OPL 1368Lowest thermal maturity containing post-oil bitumen network (0.85% VRo, n = 35)Post-Oil Bitumen Connected NetworkVitrinite (0.90% Ro; sample OPL 1366)
[500X field width is 140 microns]
500XNanopores associated with “organic matter” using ion milling and SEM (from Loucks and others, 2009)Study of Nanoporositydevelopment by Organic Matter Types and Thermal Maturity using SEM backscatter electron imaging of ion milled samples Working with Mark Curtis (OU) to sample from Known to UnknownSample Types:Solid Hydrocarbon vein deposits (grahamiteand impsonite): study of post-oil bitumenCoal(high volatile and medium volatile bituminous): study of maceralgroups (vitrinite, liptinite, inertinite)Woodford Shale:
1.low thermal maturity samples with amorphous organic matter, lamalginite, telalginite(Tasmanites), and pre-oil bitumen;
2.high thermal maturity samples with post-oil bitumen networks.2D SEM BSE Image of Lower Hartshorne Coal (1.28% Rmax) showing Organics (mostly vitrinite; dark) vs. Minerals (mostly clays; light)[SEM images are by Mark Curtis]Focused Ion Beam (FIB) milling + SEM Backscattered Imaging:Low thermal maturity (0.56% Ro; OPL 600) Woodford Shale core containing amorphous organic matter, pre-oil bitumen, and TasmanitesHigher thermal maturity (1.4% Ro; OPL 1387) Woodford Shale core containing wispy post-oil bitumen network @ 500XHigher magnification of previous slide showing nanoporosityin wispy post-oil bitumen networkAOM, lamalginite, telalginite, and pre-oil solid bitumen in Woodford Shale (OPL 601; 0.58% Ro)Low Thermal Maturity Woodford Shale
3D image from serial sectioning of 2D slices of Dual Beam Imaging (sequential ion-milling and backscatter electron imaging of a sample without changing its position)3D image of organic matter from serial sectioning of 2D slices of Dual Beam Imaging (sequential ion-milling and backscatter electron imaging of a sample without changing its position)AOM, lamalginite, telalginite, and pre-oil solid bitumen in Woodford Shale (OPL 601; 0.58% Ro)Low Thermal Maturity Woodford ShaleSEM Backscatter image is favored to ILLUSTRATE:
Distributionof organic matter (over a small area)
Abundanceof organic matter (especially amorphous organic matter and bitumen network)
Nanoporosityin organic matterRecognition of ORGANIC MATTER TYPES (to date) is favored using the light microscope (reflected white light, reflected fluorescent light, transmitted white light)
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