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Assessing Undiscovered Resources of the Barnett-Paleozoic Total Petroleum System, Bend Arch–Fort Worth Basin Province, Texas*
By
Richard M. Pollastro1, Ronald J. Hill1, Daniel M. Jarvie2, and Mitchell E. Henry1
Search and Discovery Article #10034 (2003)
*Online adaptation of presentation at AAPG Southwest Section Meeting, Fort Worth, TX, March, 2003 (www.southwestsection.org)
1U.S. Geological Survey, Denver, CO
2Humble Geochemical Services, Humble, TX
Abstract
Organic-rich Barnett Shale
(Mississippian-Pennsylvanian) is the primary source 
rock
for oil and gas that is
produced from Paleozoic reservoir rocks in the Bend Arch–Fort Worth Basin
Province. Areal distribution and geochemical typing of hydrocarbons in this
mature petroleum province indicates generation and expulsion from the Barnett at
a depocenter coincident with a paleoaxis of the Fort Worth Basin.
Barnett-sourced hydrocarbons migrated westward into reservoir rocks of the Bend
Arch and Eastern shelf; however, some oil and gas was possibly sourced by a
composite Woodford-Barnett total petroleum system of the Midland Basin from the
west.
Current U.S. Geological assessments
of undiscovered oil and gas are performed using the total petroleum system (TPS)
concept. The TPS is composed of mature source rock, known accumulations, and
area(s) of undiscovered hydrocarbon potential. The TPS is subdivided into
assessment units based on similar geologic characteristics, accumulation type
(conventional or continuous), and hydrocarbon type (oil and (or) gas).
Assessment of the
Barnett-Paleozoic TPS focuses on the continuous (unconventional) Barnett
accumulation where gas and some oil are produced from organic-rich siliceous
shale in the northeast portion of the Fort Worth Basin. Assessment units are
also identified for mature conventional plays in Paleozoic carbonate and clastic
reservoir rocks, such as the Chappel Limestone pinnacle reefs and Bend Group
conglomerate, respectively. However, Barnett continuous gas is expected to add
the greatest volume of undiscovered, technically recoverable resource.
Undiscovered Barnett Shale gas will be assessed after mapping “sweet spots” and
outlying areas of hydrocarbon potential, and by defining distributions of
drainage (cell) size and cell estimated ultimate recovery. An example of a
Barnett “sweet spot” is the Greater Newark East area where thick, siliceous
Barnett has reached the gas window, and is overlain and underlain by impermeable
limestones that contain fractures that are induced during completion.
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Introduction and BackgroundOil and
gas in the Bend Arch–Fort Worth Basin Province (U.S. Geological Survey
Province 045; see definition in a later section) of north-central Texas
are produced from carbonate- and clastic- Continuous-type accumulations include fractured shale and fractured chalk oil and gas, basin-centered gas, coal bed gas, and tight reservoir gas (Figure 1). Continuous-type accumulations typically cover large areas, have source rocks in close association with these unconventional reservoir rocks, and are mostly gas (and in some cases oil) charged throughout their extent (Schmoker, 1996). Continuous accumulations commonly have transition zones (Figure 1) that grade into more conventional accumulations (Schenk and Pollastro, 2001). Subsequent to the 1995 USGS Assessment, Schmoker and others (1996) and Kuskraa and others (1998) estimated undiscovered (also referred to as undeveloped), technically recoverable gas for the continuous Barnett fractured shale play. Using a cell-based methodology Schmoker and others (1996) estimated a mean undiscovered gas of about 3.4 trillion cubic feet (TCF). Using a similar methodology, Kuskraa and others (1998) modified the input values using more recent estimated ultimate recovery (EUR) and cell-size (drainage area) data for Barnett wells and reported a mean undiscovered volume of about 10 TCF for the Barnett. Although these mean estimates of undiscovered gas for the continuous Barnett Shale play have been ‘labeled’ USGS assessments, they are not official USGS resource numbers. However, the results of these studies, and more recent studies (Bowker, 2002) indicate that the continuous fractured Barnett Shale may contain the greatest undiscovered resource in the Bend Arch-Fort Worth Basin Province. Current USGS assessments incorporate the total petroleum systems–assessment unit (TPS-AU) method (Klett et al., 2000; Magoon and Schmoker, 2000) to estimate undiscovered oil and gas rather than the play concept method used in 1995 (Gautier et al., 1996). The total petroleum system (TPS) includes all of the elements of the petroleum system originally defined by Magoon and Dow (1996), but also incorporates those resources of the petroleum system that are yet to be discovered (Figure 2). The TPS-AU approach is preferred (USGS World Petroleum Assessment 2000) over the play-level approach because the former incorporates the assessment unit within a higher context level of the TPS. Moreover, the AU is based on similar geologic elements and hydrocarbon accumulation type and may also represent a play or group of plays. This allows for a greater understanding of the essential elements and processes within the TPS that relate to source, generation, migration, accumulation, and trapping of the undiscovered resource.
Petroleum geochemistry studies by Jarvie and others (2001), Jarvie and
Claxton (2002), and in this report indicates that the organic-rich
Barnett Shale is the primary source
Province Boundary, Structural Elements, and Tectonic History
The boundary of USGS Province
045, Bend Arch-Fort Worth Basin, is defined by State and county lines
that closely follow U.S. Congressional Districts, rather than by
geologic elements. However, the Province boundary generally follows the
Ouachita structural front to the
Major structural features of
USGS Province 045 include the Muenster and Red River Arches to the
north, and the Bend and Lompasas Arches along the central part of the
Province. Along the eastern portion of the province is an area that
includes the Eastern and Chappel Shelves and Concho Arch, collectively
also known as the Concho Platform (Figure 3). The Mineral Wells fault
runs northeast-southwest through Palo Pinto, Parker, Wise, Denton
Counties and joins with the Newark The evolution of the Fort Worth Basin and Bend Arch structures are critical to understanding burial histories and hydrocarbon generation of the Barnett-Paleozoic TPS. The asymmetrical, wedge-shaped Fort Worth Basin is a peripheral Paleozoic foreland basin with about 12,000 ft of strata preserved in its deepest northeast portion and adjacent to the Muenster Arch and Ouachita structural belt; the approximate location of its present-day axis is shown in Figure 3. The basin is similar to other basins of the Ouachita structural belt, such as the Black Warrior, Arkoma, Val Verde, and Marfa Basins that formed in front of the advancing Ouachita structural belt as it was thrust onto the margin of North America. Thrusting occurred during a late Paleozoic (Late Mississippian and Early Pennsylvanian time) episode of plate convergence (Flippen, 1982). The Bend Arch extends northward from the Llano Uplift; it is a broad subsurface, north-plunging, positive structure. The arch formed as a hingeline by (1) down-warping of its eastern flank due to subsidence of the Fort Worth Basin during early stages of development of the Ouachita structural belt in the Late Mississippian, and (2) westward tilting in the late Paleozoic, which formed the Midland Basin. There is some disagreement on the structural history of the Bend Arch. Flippen, (1982) suggested that it acted as a fulcrum and is a flexure and structural high and that only minor uplift occurred in the area to form the unconformable surface above the Comyn Limestone. In contrast, Cloud and Barnes (1942) suggested that periodic upwarp of the Bend flexure from mid-Ordovician through Early Pennsylvanian time resulted in several erosional unconformities. The Red River Arch and the Muenster Arch also became dominant structural features during Late Mississippian and Early Pennsylvanian time (Flippen, 1982).
General Stratigraphy and Petroleum Production history
The stratigraphic section of
the Bend Arch–Fort Worth Basin Province is generalized in
Figure 4.
Producing intervals, vertical distribution of total petroleum system
elements, and proposed assessment units for the Barnett-Paleozoic TPS
are also shown in Figure 4. Oil and gas production from rocks of
Ordovician, Mississippian, and Early Pennsylvanian age in the TPS is
mostly from carbonate The sedimentary section in the Fort Worth Basin is underlain by Precambrian granite and diorite. Cambrian rocks include granite conglomerate, sandstones, and shale that are overlain by marine carbonate rocks and shale (Flippen, 1982). No production has been reported from Cambrian rocks. The Silurian, Devonian, Permian, Jurassic, and Triassic are absent in the Fort Worth Basin (Flippen, 1982).
From Cambrian to
Mississippian time, the area that is now the Fort Worth Basin was part
of a stable cratonic shelf with deposition dominated by carbonates
(Burgess, 1976). Ellenburger Group carbonate rocks represent a broad
epeiric carbonate platform that covered virtually all of Texas during
the Early Ordovician. A pronounced drop in sea level at the end of
Ellenburger deposition resulted in prolonged platform exposure and
development of extensive karst features in the upper part of the
carbonate The Barnett Shale was deposited over the resulting unconformity. Provenance of the terrigenous material that constitutes the Barnett Shale was from Ouchita thrust sheets and the reactivation of older structures such as the Muenster Arch. Clastic rocks of similar provenance dominate the Pennsylvanian part of the stratigraphic section in the Bend Arch-Forth Worth Basin. With progressive subsidence of the basin during the Pennsylvanian, the western basin hinge line and carbonate shelf, represented by carbonate rocks of the Comyn, Marble Falls, Big Saline, and Caddo Formations, continued to migrate westward. Deposition of the thick basinal clastic rocks of the Atoka, Strawn, and Canyon Formations occurred at this time (Walper, 1982). These Middle and Late Pennsylvanian age rocks consist mostly of sandstones and conglomerates with fewer and thinner limestone beds (Figure 4). Wolfcampian age sandstones also produce oil and gas along the western portion of the USGS Province 50 and on the Bend Arch, Eastern Shelf, and Concho platform. Shows of oil and gas were first encountered within Bend Arch-Fort Worth Basin Province during the mid-nineteenth century while drilling water wells. Some petroleum exploration began at the end of the Civil War, and the first commercial oil discoveries occurred in the early 1900’s (Ball and Perry, 1996). By 1960, USGS Province 045 reached a mature stage of exploration and development, as demonstrated by the high density and distribution of well penetrations (see Ball and Perry, 1996), and production wells (Figure 3).
Cumulative production in USGS
Province 045 from conventional reservoirs prior to the 1995 USGS
Assessment was about 2 billion barrels of oil (BBO) and 7 trillion cubic
feet of gas (TCFG). Cumulative gas production through 2001 from the
continuous Barnett fractured shale play in Wise and Denton counties was
about 440 BCF (Swindell, 2002). Cumulative gas production from the
Barnett Shale for the first half of 2002 was 94 BCF (Texas Railroad
Commission, 2202); annual production for 2002 is estimated to be about
200 BCF. Currently, more than 2.5 TCF of proven gas reserves are
assessed for Newark Barnett-Paleozoic Total Petroleum System
Oil and gas is produced from
reservoirs rocks of Paleozoic age within USGS Province 045. Organic
geochemical analyses of samples of oil and gas from the Fort Worth Basin
from this study and those reported by Jarvie and others (2001), indicate
that these hydrocarbons were derived from a single source
Source
The primary source
The Barnett Shale source Average total organic carbon (TOC) content in the Barnett Shale is about 4% (by weight) and TOC is as high as about 12% in samples from outcrops along the Llano uplift on the south flank of the Fort Worth Basin (Henk et al., 2000; Jarvie et al., 2001). The highest average TOC for the Barnett Shale appears to follow a depocenter that is coincident with a paleo-axis of the Fort Worth Basin (Figure 3).
The Barnett Shale has
geochemical characteristics similar to other Devonian-Mississippian
black shales found elsewhere in the U. S. (e.g., Woodford, Bakken, New
Albany, and Chattanooga Formations). These black shales all contain
oil-prone organic matter (Type II kerogen) based on hydrogen indices
greater than 350milligrams of hydrocarbons per gram of TOC and generate
a similar type of high quality oil (low sulfur, >30 API gravity). Oils
found in the far western and northern portions of USGS Province 50 are
all typed as Barnett-sourced oils. Although decomposition of kerogen
cracking is a source of oil and gas from the Barnett Shale, the
principal source of gas in the Newark Low
levels of maturation in the Barnett Shale at vitrinite reflectance (Ro),
estimated at 0.6-0.7%, yields oils of 38o API gravity in
Brown County. The oils found in Shackelford, Throckmorton, and Callahan
Counties as well, as in Montague County (Figure 3), are derived from the
Barnett Shale at the middle of the zone of oil generation (oil window)
thermal maturities levels (about 0.9% Ro). Although
condensate is associated with gas production in Wise County, the Barnett
source
Thermal maturity of Barnett
Shale can also be derived from TOC and Little
or no data are available on the variability of the Barnett Shale organic
matter content and type outside of Newark
In contrast, low maturity
Barnett Shale from outcrops in Lampasas County have initial TOC values
averaging about 12% with hydrocarbon potentials averaging 1035 BO/AF. A
good average value for the Barnett Shale is derived from the Mitcham #1
well in Brown County in which TOC is measured at 4.2% and the
hydrocarbon potential is 354 BO/AF. Using these data we can determine
that the TOC values will decrease 36% during maturation from the
immature stage to the gas-generation window. Samples from the T. P.
Simms well in the Newark
This study found a poor
correlation between measured Ro and present-day burial depth
for the Barnett Shale, as did Bowker (2002). Vitrinite iso-reflectance
contours commonly cross-cut both basin structure and structure contours
on the top of the Barnett Shale. Similarly, samples of Barnett Shale in
the deepest part of the Fort Worth Basin along the southwest flank of
the Muenster Arch in Denton County, record lower Ro than the
shales at shallower depths to the
The Barnett Shale is
thermally mature for hydrocarbon generation over most of its area within
USGS Province 045 (Figure 3). The Barnett source
In the main gas-producing
area of fractured Barnett Shale, the gas generation window is along a
trend that is sub-parallel to the Ouchita thrust front (Bowker, 2002).
Jarvie and others (2001) and Bowker (2002) reported that the British
Thermal Unit (BTU) content of Barnett gas is directly proportional to Ro
levels. Oil and gas windows for the Barnett source
Reservoir rocks of the Barnett-Paleozoic TPS include both clastic and carbonate rocks ranging in age from Ordovician to Early Permian (Wolfcampian); they are listed in the stratigraphic section and total petroleum system distribution chart of Figure 4. Most production from conventional reservoirs is from rocks of Pennsylvanian age, whereas the only recognized production from an unconventional (continuous) accumulation is from the Mississippian-Pennsylvanian fractured Barnett Shale. Conglomerate of the Pennsylvanian Bend Group is the main producing reservoir at giant Boonsville Field of Wise and Jack Counties with cumulative production through 2001 of more than 3 TCFG (Swindell, 2002). Jarvie and others (2001) reported that oil sourced from the Barnett Shale is produced from numerous reservoir rocks in the Bend Arch-Fort Worth Basin, including Barnett Shale, Caddo Formation, Canyon Group, Chappel Limestone, Bend Group,and Ellenburger Group (Figure 4). Additional reservoir rocks of the Barnett-Paleozoic TPS considered in this report are in the Viola Limestone, Marble Falls Limestone, Atoka Formation, Strawn Group, and Cisco Group (Figure 4). Historical production summaries for many of these reservoirs are given in Ball and Perry (1996).
Traps for conventional
hydrcocarbon accumulations are mostly stratigraphic for carbonate Proposed Assessment Units for the Barnett-Paleozoic TPS The USGS assesses conventional accumulations using distributions of size and number of oil and gas fields. In contrast, continuous-type accumulations are assessed using a distribution of both well-cell size (drainage area) and well EURs (Schmoker et al., 1996). Five conventional assessment units are initially proposed for the Barnett-Paleozoic TPS in the Bend Arch-Fort Worth Basin Province and are listed in Table1; these assessment units are also compared with plays defined for the 1995 USGS Assessment. Most historical production in USGS Province 045 has been from extensively explored conventional clastic reservoirs of Pennsylvanian age, particularly the conglomerates and sandstones of the Bend Group (Morrowan and Atokan) and fluvial-deltaic sandstones of the Strawn Group (Desmoinesian) (Figure 3).
Continuous accumulations
commonly cover large geographic areas. Thus, multiple assessment units
are commonly defined for a particular continuous accumulation, such as
the Barnett Shale, which commonly are based on differences primarily
with regard to (1) geologic facies, thickness, structure; (2)
hydrocarbon type; (3) organic geochemistry; (4) thermal maturation (oil-
and gas-generation windows); (5) drainage area; and (6) well production
(EUR). For example, assessment units that define “sweet spots” commonly
have greater near-future resource volume potential because drainage
areas are commonly smaller and have higher mean well EUR than other
areas of lesser potential. The Greater Newark Fractured Barnett Shale Continuous Oil and Gas
Oil and gas are produced from
fractured Barnett Shale in the Bend Arch-Forth Worth Province.
High-quality (35-40° API gravity, low sulfur) oil is produced from the
Barnett Shale in northern and western portions of the province where the
Barnett exhibits low thermal maturity (Ro about 0.6%). Oils
of similar quality (40-50° API gravity), and condensates associated with
gas are produced in Wise County where the Barnett is of higher thermal
maturity. Gas production is from hydraulically-fractured black
siliceous shale. Calorific values of gases from Newark The main producing facies of the Barnett is a black, organic-rich siliceous shale with a mean composition, by weight, of about 45% quartz, 27% clay (mostly illite/smectite, and illite), 10% carbonate (calcite, dolomite, and siderite), 5% feldspar, 5% pyrite, and 5% TOC (Lancaster et al., 1993; Henk et al., 2000; Bowker, 2002). Average porosity in the productive portions of the Barnett is about 6% and matrix permeability is measured in nanodarcies (Lancaster et al., 1993; Bowker, 2002).
The lithology and
petrophysical characteristics of units above and below the Barnett Shale
are critical to gas production within the Barnett continuous
accumulation. The Newark
A minimum of three assessment
units (Table 1) is proposed for the Barnett Shale continuous
accumulations, each with different geologic and production
characteristics: (1) a Newark
The siliceous nature of the
Barnett Shale, and its relation to fracture enhancement in the area of
Newark
Historically, typical EURs
for Barnett gas wells at Newark
A Barnett-Paleozoic Total
Petroleum System has been defined for the Bend Arch-Fort Worth Basin
Province, USGS Province 045. Distribution and geochemical typing of
hydrocarbons produced from Paleozoic reservoirs rocks indicate
generation, expulsion and emplacement from the organic-rich,
Mississippian-Pennsylvanian Barnett Shale. Reservoir rocks of the
Barnett-Paleozoic TPS are carbonate and clastic rocks that range in age
from Ordovician to Permian (Wolfcampian). Reservoirs are sealed by
thick shale or dense, impermeable carbonate rocks. The boundaries for
the Barnett-Paleozoic TPS are major geologic structures to the north,
south, and
TOC content in the Barnett
Shale averages 4% and consists of oil-prone Type II kerogen. Oils were
initially generated from the decomposition of organic matter in the
Barnett Shale at low levels of thermal maturities, whereas gas produced
from the greater Newark Preliminary analysis of the Bend Arch-Fort Worth Basin Province has identified five conventional and three continuous assessment units for assessing undiscovered, technically recoverable resources of the Barnett-Paleozoic TPS. The three continuous assessment units are areas of potential Barnett Shale production that are defined by both geologic conditions and geochemical and thermal maturity parameters. The greatest volume of undiscovered resource in the Barnett-Paleozoic TPS is expected from continuous gas accumulations within the Barnett Shale. Allard, J., 2000, Barnett Shale play hot in North Texas: Landman, p. 26-28, Accessed June 2002 at URL http://www.landmand.org. Ball M. M., and W. J. Perry, 1996, Bend Arch-Fort Worth Basin Province (045), in D. L. Gautier, G. L. Dolton, K. I. Takahashi, and K. L. Varnes, eds., 1995 National assessment of United States oil and gas resources – Results, methodology, and supporting data: U.S. Geological Survey Digital Data Series DDS-30, Release 2, [CD-ROM]. Bowker, K., 2002, Recent developments of the Barnett Shale play, Fort Worth Basin, in Law, B.E. and Wilson, M., eds., Innovative Gas Exploration Concepts Symposium: Rocky Mountain Association of Geologists and Petroleum Technology Transfer Council, October, 2002, Denver, CO, 16 p. Comer, J. B, 1991, Stratigraphic analysis of the Upper Devonian Woodford Formation, Permian Basin, West Texas and Southeastern New Mexico: Texas Bureau of Economic Geology Report of Investigations 201, 63 p. Devon Energy Corporation, 2002, Mid-year company operations update and Barnett Shale school, June 20, 2002: Accessed August 2002 at URL www.dvn.com. Flippin, J. W., 1982, The stratigraphy, structure, and economic aspects of the Paleozoic strata in Erath County, North-Central Texas, in C. A. Martin, ed., Petroleum geology of the Fort Worth Basin and Bend Arch area: Dallas Geological Society, p. 129-155. Gautier, D. L., G. L. Dolton, K. I. Takahashi, and K. L. Varnes, K. L., eds., 1996, 1995 National assessment of United States oil and gas resources – Results, methodology, and supporting data: U.S. Geological Survey Digital Data Series DDS-30, Release 2, one CD-ROM. Grayson, R. C. and G. K. Merrill, eds., 1991, Carboniferous geology and tectonic history of the Southern Fort Worth (Foreland) Basin and Concho Platform, Texas: AAPG, 1991 Annual Convention, Dallas Geological Society Guidebook, Field Trip No. 13, 67 p. Grayson, R. C., Jr., G. K. Merrill, L. L. Lambert, and M. J. Pranter, 1991, Carboniferous geology and tectonic history of the southern Fort Worth (foreland) Basin and Concho Platform, in R. C. Grayson and G. K. Merrill, eds., Carboniferous geology and tectonic history of the Southern Fort Worth (foreland) Basin and Concho Platform, Texas: AAPG, 1991 Annual Convention, Dallas Geological Society Guidebook, Field Trip No. 13, p. 3-67. Hall, J., 2002, Barnett Shale geology, in Devon Energy Corporation, Mid-year operations update and Barnett Shale school, June 20, 2002: Accessed August 2002 at URL www.dvn.com. Henk, F., J. Breyer, and D. M. Jarvie, 2000, Lithofacies, petrology, and geochemistry of the Barnett Shale in conventional core and Barnett Shale outcrop geochemistry [abs], in L. Brogden, ed., Barnett Shale Symposium, Fort Worth Texas, Oil Information Library of Fort Worth, Texas, p. 7. Jarvie, D. M., B. L. Claxton, F. Henk, and J. T. Breyer, 2001, Oil and shale gas from the Barnett Shale, Fort Worth Basin, Texas [abs.]; AAPG Annual Meeting, Program and Abstracts, p. A100. Jarvie, D. M., and B. L. Claxton, 2002, Barnett Shale oil and gas as an analog for other black shales [abs.]: AAPG Midcontinent Meeting, New Mexico. Kerans, C., 1988, Karst-controlled reservoir heterogeneity in Ellenburger Group carbonates of West Texas: AAPG Bulletin, v. 7, p. 1160-1183. Klett, T. R., J. W. Schmoker, and T. S. Ahlbrandt, 2000, Assessment hierarchy and initial province ranking, Chapter AR, in U.S. Geological Survey World Energy Assessment Team, U.S. Geological Survey World Petroleum Assessment 2000 – Description and results, USGS Digital Data Series DDS-60, Version 1.0, CD-ROM, Disk one, 31 p. Kuuskraa, V. A., G. Koperna, J. W. Schmoker, and J. C. Quinn, 1998, Barnett Shale rising star in Fort Worth Basin: Oil and Gas Journal, v. 96, no. 21, p. 71-76. Lancaster, D. E., S. McKettta, and P. H. Lowry, 1993, Research findings help characterize Fort Worth Basin’s Barnett Shale: Oil and Gas Journal, v. 91, p. 59-64. Magoon, L. B., and W. G. Dow, 1994, The petroleum system, in L. B. Magoon, and W. G. Dow, eds., The Petroleum system – From source to trap: AAPG Memoir 60, p. 3-24. Magoon, L. B., and J. W. Schmoker, 2000, The total petroleum system – The natural fluid network that constrains the assessment unit, Chapter PS, in U.S. Geological Survey World Energy Assessment Team, U.S. Geological Survey World Petroleum Assessment 2000 – Description and results, USGS Digital Data Series DDS-60, Version 1.0, CD-ROM, Disk one, 31 p. Mapel, W. J., R. B. Johnson, G. O. Bachman, and K. L. Varnes, 1979, Southern Mid-Continent and southern Rocky Mountains Region, in L. C. Craig, and W. C. Connor, eds., Paleotectonic investigations of the Mississippian System in the United States: Part 1 – Introduction and regional analyses of the Mississippian System: U.S. Geological Survey Professional Paper 1010, p. 161-187. Reeves, S., 2002, Gas shales – Production and potential: Conference on gas shales – Production and potential, Strategic Research Institute, June 2002, Denver, CO, 40 p. Schenk, C. J., and R. M. Pollastro, 2001, Natural gas production in the United States: National Assessment of Oil and Gas Series, U.S. Geological Survey Fact Sheet FS-113-01, 2 p. Schmoker, J. W., 1996, Method for assessing continous-type (unconventional) hydrocarbon accumulations, in D. L. Gautier, G. L. Dolton, K. I. Takahashi, and K. L. Varnes, eds., 1996, 1995 National assessment of United States oil and gas resources – Results, methodology, and supporting data: U.S. Geological Survey Digital Data Series DDS-30, Release 2, [CD-ROM]. Schmoker, J. W., C. J. Quinn, R. A. Crovelli, V.F. Nuccio, and T. C. Hester, 1996, Production characteristics and resource assessment of the Barnett Shale continuous (unconventional) gas accumulation, Fort Worth Basin, Texas: U.S. Geological Survey Open-File Report 96-254, 20 p. Shirley, K., 2002, Barnett Shale living up to potential: AAPG Explorer, v. 23, no. 7, p.18-27. Sloss, L. L., 1976, Areas and volumes of cratonic sediments, western North America and eastern Europe: Geology, v. 4, p. 272-276.
Swindell, G.
S, 2002, Newark Walper, J. L., 1982, Plate tectonic evolution of the Fort Worth Basin, in Martin, C.A., ed., Petroleum geology of the Fort Worth basin and Bend arch area: Dallas Geological Society, p. 237-251. ACKNOWLEDGMENTSThe authors are grateful for the constructive reviews of the manuscript by Deborah Higley, Michael Brownfield, and William Keefer. We would also like to thank Republic Energy, Inc. for permission to sample several of their oil and gas wells for geochemical analyses in hopes to further understand the Barnett-Paleozoic Total Petroleum System. This study has also benefited from discussions with the Discovery Group, Denver, CO. |
Figure
1. Generalized diagram showing categories of conventional and continous
oil and gas accumulations.
Figure
2. Schematic plan view of a Total Petroleum System showing pod of
mature source 
Figure
3. Map showing major structural elements (black lines), oil (green
dots) and gas (red dots) well production, location of Newark 
Figure
4. Generalized stratigraphic subsurface section of USGS Bend Arch-Fort
Worth Basin Province showing stratigraphic extent of Barnett-Paleozoic
Total Petroleum System,
Figure
5. Events chart for Mississippian-Pennsylvanian Barnett-Paleozoic Total
Petroleum System (TPS)
Figure
6. (A) Location map and (B) generalized cross section AA’ of north Fort
Worth Basin area showing main gas- producing area of continuous Barnett
Shale accumulation at Newark 
Table 1. Plays identified in
the 1995 USGS National Oil and Gas Assessment (after Ball and Perry,
1996) and proposed assessment units (AU) for 2003 USGS National Oil and
Gas Assessment of the Barnett-Paleozoic