Indiana Geological Survey Reservoir Characteristics and Gas Production Potential of Woodford Shale in the Southern Midcontinent John B. Comer Indiana Geological Survey Indiana University 812-855-2687 jcomer@indiana.edu

Distribution of Devonian Black Shale Modified from Juergen Schieber, 2004

Woodford Lithofacies in the Southern Midcontinent Black shale Siltstone Dolostone Chert Sandstone Mudstone Bypassed settings Proximal and basin centers Distal to open ocean Proximal and locally derived Local

Log Characteristics Texas and New Mexico Pan American No. 1 Walker Shell No. 1 Chriesman Mobil No. 1918 Parks Unit 2 Upper Woodford is missing and middle Woodford is truncated in the Lea County, New Mexico, and Cochran County, Texas, wells indicating that there was a period of uplift and erosion before the Mississippian Limestone was deposited. In the Midland County, Texas, well, lower Woodford is missing due to onlap over the Central Basin Platform. A telescoped section of Woodford containing all three units is present in Glasscock County, Texas. Ellison (1950) suggested that telescoped sections indicate contemporaneous uplift during Woodford deposition. For more details see Comer (1991). Shell No. 5 Pacific Royalty Reference log from Ellison (1950) Comer (1991) Fig. 7

Fractured Woodford Shale Reservoirs North Aylesworth Field Marshall County, Oklahoma Texaco 1-K Drummond, 11-6S-6E Comer (1992) location A33; Comer (1987) Fig. 5e Southeast Joiner City Field Carter County, Oklahoma California No. 1 Mullen, 29-5S-2W Comer (1992) location A21; Comer (1987) Fig. 5a Oil reservoirs in the North Aylesworth Field include Woodford Shale, the overlying Sycamore Limestone, and the underlying Misener Sandstone and Hunton Group. Oil reservoirs in the Southeast Joiner City Field include Woodford Shale and the underlying Bois D’Arc and Chimney Hill Formations in the Hunton Group. 3,065 ft 7.8 % TOC 8,983 ft 5.5 % TOC 1.0 mm 0.2 mm Vertical fractures and stylolites filled with bitumen Tension gash filled with chert Recrystallized Radiolaria

Comer (1992) location A25; Comer (1987) Fig. 4a-d Fractured Woodford, Anadarko Basin Columbia Fuel #1 Rainy Mountain, Kiowa County, Oklahoma, 23-6N-15W, 760 ft Comer (1992) location A25; Comer (1987) Fig. 4a-d 8.1 % TOC 0.61 % Ro Bitumen Calcite Superposition of phases filling these fractures shows that calcite formed first and bitumen invaded the remaining porosity before the fractures were completely mineralized. Calcite precipitates from aqueous solution and represents an early period of time when the Woodford was water wet. Bitumen was generated from indigenous type II kerogen and represents the period of time when primary migration occurred during the early oil generation stage of thermal maturation. With oil generation the Woodford became oil wet and the pore system became oil saturated. Bitumen filled fractures are characteristic of the Woodford in southern Oklahoma and indicate that the bitumen invaded fractures shortly after they formed. Fractures mostly formed during tectonic adjustments associated with Late Paleozoic orogenic activity. 1 mm Core diameter = 2 inches

Comer (1991) location C2, sample C2-5 Fractured Woodford, Permian Basin Humble No. 43 Yarborough & Allen, Ward County, Texas, Section 66, E. J. Brady Survey Comer (1991) location C2, sample C2-5 Calcite 7175 ft Fractures in Woodford Shale from the Permian Basin formed early and are mostly calcite filled. Fractures are highly deformed and the calcite commonly is twinned due to compaction and shearing . Bitumen is rarely found in fractures and is restricted to the small residual cavities or vugs that formed when calcite crystals growing outward from opposite walls of a fracture failed to join. 10.1 % TOC 0.55 % Ro Type II Kerogen 1 cm 0.2 mm

Interbedded Black Shale and Chert Lithofacies, Southern Oklahoma Arbuckle Mountain Uplift outcrop, Murray County, Oklahoma, 1-2S-2E Comer (1992) location OK26, Hwy 110 2 miles north of Dougherty; Comer (1987) Fig. 7a Chert Black Shale Chert Black Shale Chert Black Shale Interbedded organic-rich, biogenic chert and black shale are characteristic of Woodford in south-central and southeastern Oklahoma. Chert 0.2 m

Black Shale and Chert Petrology, Southern Oklahoma Comer (1992) location OK35 Arbuckle Mtn Uplift 25-2S-1E; Comer (1987) Fig. 7c Comer (1992) location OK 55 Ouachita frontal zone 4-2N-15E; Comer (1987) Fig. 7b Black Shale Highly compacted Flattened Tasmanites spores (T) Amorphous Type II organic matter (AOM) Little or no chert Chert Tasmanites spores (T) uncompacted or slightly flattened (early chert (CT) cementation) Amorphous Type II Organic Matter (uncompacted) Well indurated, brittle, and tightly sealed Tasmanites are marine algal spores that are hollow and easily flattened during compaction unless cementation occurs very soon after deposition. Up to 35 % TOC Up to 6.4 % TOC 0.2 mm 0.2 mm

Chattanooga Shale, Ozark Uplift, Belle Vista, Benton County, Arkansas Boone Formation St. Joe Member (Mississippian) Chattanooga Shale (Devonian) 2.1 % TOC 1.11 % Ro Mixed marine/terrestrial kerogen US 71 12-20N-31W Comer (1992) location AR1

Black Shale – Sandstone Association, Ozark Uplift Sylamore Sandstone Type Area, 21-15N-11W, Stone County, Arkansas Interbedded black shale and medium-grained supermature quartzarenite 8.5 ft thick; Quartz inherited from Middle Ordovician sandstones Comer (1992) location AR9 Comer (1987) Fig. 3a-c Phosphate Black Shale Oil Residue Black Shale 3.5 % TOC (avg) 0.83 % Ro (avg) Black Shale consists of zones of amorphous marine Type II kerogen terrestrial Type III kerogen mixed marine and terrestrial kerogen Quartz 0.75 mm 0.2 mm

Black Shale Characteristics Mobil No. 1918 Parks Unit 2, Midland County, Texas, Section 14, Block 40, C. F. O’Neal Survey 11,544 ft, 3.1 % TOC Comer (1991) location C1, sample C1-5 Parallel laminae Abundant pyrite Fine grain size Black color High radioactivity Abundant organic carbon Amorphous (marine) type II kerogen 1 cm 11,555 ft 4.2 % TOC Comer (1991) location C1, sample C1-10, Fig. 4a 3 mm

Siltstone Characteristics Shell A No. 1 Williamson, Gaines County, Texas, Section 110, Block H, D&WRR Survey, 13,064 ft Black Shale Bioturbated Siltstone Pyrite 1 cm Comer (1991) location C11, sample C11-10

Siltstone Characteristics Shell A No. 1 Williamson, Gaines County, Texas, Section 110, Block H, D&W RR Survey, 13,064 ft Comer (1991) location C11, sample 11-10, Fig. 5h Siltstone Characteristics Subequal random mixture of detrital dolomite (48%) and quartz (52%) Median grain size is 0.05 mm (coarse silt) for both dolomite and quartz Dolomite is angular and abraded with random orientations and uniform texture Siltstone is dense and well indurated Much of the dolomite in siltstones is resedimented from shallow-water evaporitic settings. See Comer (1991) for detailed discussion. 0.1 mm

Siltstone Depositional Processes Silt was deposited by bottom flows Ripple wavelength ~ 1.5 cm C (Rippled) B (Flat) Bouma Sequence A (Graded) Scoured Base Hybrid quartz/dolomite siltstones like the ones shown here were deposited from bottom flows that were mostly storm-generated . See Comer (1991). Humble No. 1 A. E. State, Lea County, New Mexico, 16-15S-33E, 13,768 ft Comer (1991) location C3, sample C3-5, Fig. 5e 3 mm

Lithologic Variations, Texas and New Mexico Modified from Comer (1991) Fig. 9 Upper left panel: Siltstones are most abundant in two different types of locations (1) proximal settings near emergent source areas and (2) deep basin depocenters where bottom flows finally converge. Upper right panel: Shallow-water sedimentary structures include burrows and desiccation cracks. They represent depositional settings that were topographically elevated during the Late Devonian. Lower left panel: Dolomite is more abundant that quartz in shallow-water settings along the flank of the Eastern Shelf, on the Central Basin Platform, and on shoals in the far western part of the basin. The distribution suggests that these were the areas where most of the contemporaneous dolomitization was occurring. Lower right panel: Biogenic chert (predominantly recrystallized Radiolaria) is found mostly along the Central Basin Platform and the eastern flank of the Midland Basin suggesting that these areas were bypassed by bottom flows and experienced intrabasinal upwelling.

Woodford Resource Potential For TOC and thermal maturity data see Comer (1992). Modified from Comer (2005)

Woodford Resource Potential In-Place Estimates Based On Hydrogen Mass Balance 600 x 1012 ft3 60 x 109 bbl 4.4 x 1012 ft3 70 x 109 bbl 0.24 x 1012 ft3 For a detailed explanation of the calculations used to make these estimates, see Comer (2005). TOTAL RESOURCE POTENTIAL Total Estimated Oil-in-Place 130 x 109 bbl Total Estimated Gas-In-Place 600 x 1012 ft3 Modified from Comer (2005)

Woodford Resource Potential For TOC and thermal maturity data see Comer (1991). Modified from Comer (2005)

Woodford Resource Potential In-Place Estimates Based On Hydrogen Mass Balance 35 x 109 bbl 0.11 x 1012 ft3 84 x 109 bbl 9.0 x 1012 ft3 220 x 1012 ft3 For a detailed explanation of the calculations used to make these estimates, see Comer (2005). TOTAL RESOURCE POTENTIAL Total Estimated Oil-in-Place 120 x 109 bbl Total Estimated Gas-In-Place 230 x 1012 ft3 Modified from Comer (2005)

Conclusions Unconventional gas discoveries in Woodford Shale are likely in both the Anadarko and Permian Basins and adjacent provinces where Woodford Shale is thermally mature Fractures are common Competent lithofacies (chert, siltstone, dolostone, sandstone, silty black shale) are abundant Areas having greatest gas production potential and most prospective lithologies are the Anadarko Basin in Oklahoma (siltstone and silty black shale) Arkoma Basin in Oklahoma and Arkansas (silty black shale) Frontal zone of Ouachita fold belt in Oklahoma (chert) Delaware Basin in Texas and New Mexico (siltstone and silty black shale) Val Verde and Midland Basins in Texas (siltstone and silty black shale)

Key References Comer, J. B., 1991, Stratigraphic analysis of the Upper Devonian Woodford Formation, Permian Basin, West Texas and southeastern New Mexico: Austin, Texas, Bureau of Economic Geology, Report of Investigations 201, 63 p. Comer, J. B., 1992, Organic geochemistry and paleogeography of Upper Devonian formations in Oklahoma and northwestern Arkansas, in K. S. Johnson, and B. J. Cardott, eds., Source Rocks in the Southern Midcontinent, 1990 Symposium: Norman, Oklahoma, Oklahoma Geological Survey, Circular 93, p. 70-93. Comer, J. B., 2005, Facies distribution and hydrocarbon production potential of Woodford Shale in the southern Midcontinent, in B. J. Cardott, ed., Unconventional Energy Resources in the Southern Midcontinent, 2004 Symposium: Norman, Oklahoma, Oklahoma Geological Survey, Circular 110, p. 51-62. Comer, J. B., and H. H. Hinch, 1987, Recognizing and quantifying expulsion of oil from the Woodford Formation and age-equivalent rocks in Oklahoma and Arkansas: American Association of Petroleum Geologists Bulletin, v. 71, p. 844-858. Ellison, S. P., 1950, Subsurface Woodford black shale, west Texas and southeast New Mexico: Austin, Texas, Bureau of Economic Geology, Report of Investigations 7, 20 p.