Changes

==Previous research==

==Previous research==

During the 1970s, the U.S. Department of Energy initiated the Eastern Gas Shales Project (EGSP) to study the geology and production potential of the multiple organic-rich shales located in the northeastern United States. A total of 595 separate reports, articles, and reviews were generated by researchers working under the EGSP, leading to a voluminous available database on all the eastern shales, including the Marcellus Shale. In the Appalachian Basin, this enormous research effort was mostly directed toward the study of the controls on production within the Big Sandy field and to identify new major areas of Devonian shale-gas potential. These studies led the way to a significant expansion of the Big Sandy field into southwestern and central West Virginia and parts of southeastern Ohio. A large segment of the EGSP can be accessed from the National Energy Technology Laboratory (2007).

During the 1970s, the U.S. Department of Energy initiated the Eastern Gas Shales Project (EGSP) to study the geology and production potential of the multiple organic-rich shales located in the northeastern United States. A total of 595 separate reports, articles, and reviews were generated by researchers working under the EGSP, leading to a voluminous available database on all the eastern shales, including the Marcellus Shale. In the Appalachian Basin, this enormous research effort was mostly directed toward the study of the controls on production within the Big Sandy field and to identify new major areas of Devonian shale-gas potential. These studies led the way to a significant expansion of the Big Sandy field into southwestern and central West Virginia and parts of southeastern Ohio. A large segment of the EGSP can be accessed from the National Energy Technology Laboratory.<ref>National Energy Technology Laboratory, 2007, [http://www.netl.doe.gov/publications/cdordering.html Archive of unconventional gas resources program].</ref>

==History of the Appalachian basin shale-gas development==

==History of the Appalachian basin shale-gas development==

[[File:M97Ch4FG1.jpg|400px|thumb|{{figure number|1}}A map depicting the historical trends of shale-gas production in the Appalachian Basin and the Marcellus Shale play trend. Map includes present boundaries and names of states, U.S.A. WI = Wisconsin; IL = Illinois; DC = District of Columbia; VT = Vermont; MA = Massachusetts; CT = Connecticut.]]

[[File:M97Ch4FG1.jpg|400px|thumb|{{figure number|1}}A map depicting the historical trends of shale-gas production in the Appalachian Basin and the Marcellus Shale play trend. Map includes present boundaries and names of states, U.S.A. WI = Wisconsin; IL = Illinois; DC = District of Columbia; VT = Vermont; MA = Massachusetts; CT = Connecticut.]]

The Appalachian Basin has a well-established history of shale-gas development ([[:File:M97Ch4FG1.jpg|Figure 1]]). The discovery and commercial use of gas from Devonian shales in the early 1820s in Fredonia, New York, is generally recognized as the birthplace of the natural gas industry. This significantly predates the Drake oil discovery in Titusville, Pennsylvania, in 1859. By 1860, a series of shallow shale-gas fields were developed in a fairway along the Lake Erie shoreline extending from Fredonia, New York, southwest toward the city of Sandusky, Ohio (Harper, 2008). Accurate data for these wells are scarce, but the likely black shale formations produced include the Dunkirk, Rhinestreet, Middlesex, and to a lesser extent the Marcellus. The initial reported gas rates were commonly high, but actual production rates and pressures were low and are not considered commercial by today's standards. These shallow wells were used mainly for domestic and light industrial purposes and were extensively developed from the 1860s through the mid-1900s.

The Appalachian Basin has a well-established history of shale-gas development ([[:File:M97Ch4FG1.jpg|Figure 1]]). The discovery and commercial use of gas from Devonian shales in the early 1820s in Fredonia, New York, is generally recognized as the birthplace of the natural gas industry. This significantly predates the Drake oil discovery in Titusville, Pennsylvania, in 1859. By 1860, a series of shallow shale-gas fields were developed in a fairway along the Lake Erie shoreline extending from Fredonia, New York, southwest toward the city of Sandusky, Ohio.<ref>Harper, J. A., 2008, The Marcellus Shale: An old “new” gas reservoir in Pennsylvania: Pennsylvania Geology, v. 38, no. 1, p. 2–13.</ref> Accurate data for these wells are scarce, but the likely black shale formations produced include the Dunkirk, Rhinestreet, Middlesex, and to a lesser extent the Marcellus. The initial reported gas rates were commonly high, but actual production rates and pressures were low and are not considered commercial by today's standards. These shallow wells were used mainly for domestic and light industrial purposes and were extensively developed from the 1860s through the mid-1900s.

The first major shale discovery in the Appalachian Basin was in 1921 in northeastern Kentucky, which established the Big Sandy field. To date, a total of more than 21,000 wells have been drilled in the Big Sandy field in eastern Kentucky, southern West Virginia, southern Ohio, and southwestern Virginia. The primary target in the Big Sandy field is the Upper Devonian Huron Shale, with contributions from the Cleveland, Rhinestreet, and Marcellus Shale intervals. Two characteristics of the Big Sandy field are its significant underpressured profile and a well-established open natural fracture network. This distinguishes the Big Sandy field from modern shale plays such as the Barnett, Fayetteville, and Haynesville shales, which have higher pressure gradients combined with lower density open natural fracture networks. These modern shale-gas plays rely more on the creation of induced artificial fractures to achieve commercial production rates than production from existing open natural fractures. To date, more than 2.5 tcf has been produced from the Big Sandy field,<ref name=Dw1986 /> and it still represents one of the top 100 gas fields in the United States. The development of the Big Sandy field continues using both vertical and horizontal drilling (Morris, 2008).

The first major shale discovery in the Appalachian Basin was in 1921 in northeastern Kentucky, which established the Big Sandy field. To date, a total of more than 21,000 wells have been drilled in the Big Sandy field in eastern Kentucky, southern West Virginia, southern Ohio, and southwestern Virginia. The primary target in the Big Sandy field is the Upper Devonian Huron Shale, with contributions from the Cleveland, Rhinestreet, and Marcellus Shale intervals. Two characteristics of the Big Sandy field are its significant underpressured profile and a well-established open natural fracture network. This distinguishes the Big Sandy field from modern shale plays such as the Barnett, Fayetteville, and Haynesville shales, which have higher pressure gradients combined with lower density open natural fracture networks. These modern shale-gas plays rely more on the creation of induced artificial fractures to achieve commercial production rates than production from existing open natural fractures. To date, more than 2.5 tcf has been produced from the Big Sandy field,<ref name=Dw1986 /> and it still represents one of the top 100 gas fields in the United States. The development of the Big Sandy field continues using both vertical and horizontal drilling (Morris, 2008).

[[File:M97Ch4FG5.jpg|400px|thumb|{{figure number|5}}A map showing the relationship of the Appalachian shale-gas plays to basement structure and position of the Rome trough. Modified from Shumaker (1996). DC = District of Columbia; MA = Massachusetts; CT = Connecticut.]]

[[File:M97Ch4FG5.jpg|400px|thumb|{{figure number|5}}A map showing the relationship of the Appalachian shale-gas plays to basement structure and position of the Rome trough. Modified from Shumaker (1996). DC = District of Columbia; MA = Massachusetts; CT = Connecticut.]]

A key regional component of the emerging Marcellus Shale play is its relationship to basement faulting. [[:File:M97Ch4FG5.jpg|Figure 5]] depicts the basement structure of the Appalachian Basin, together with major interpreted faults, the projected position of the Rome trough, and key Devonian shale and Marcellus Shale production trends. The mapped basement faults fall into two classifications: (1) those faults that are strike parallel to the basin and related to the Rome trough and (2) those faults that trend perpendicular to the strike of the basin and are interpreted as transform faults or cross-strike structural discontinuities (CSDs) (Harper and Laughrey, 1987). These basement faults represent zones of weakness believed to have been reactivated several times during the Paleozoic (Negus-DeWyss, 1979; Lee, 1980; Shumaker, 1993). In addition, reactivation caused significant structural inversion in some areas. It is likely that movement along these faults has continued well into the Quaternary, as the surface expression of several of these major features are clearly apparent on both topographic maps and satellite images.

A key regional component of the emerging Marcellus Shale play is its relationship to basement faulting. [[:File:M97Ch4FG5.jpg|Figure 5]] depicts the basement structure of the Appalachian Basin, together with major interpreted faults, the projected position of the Rome trough, and key Devonian shale and Marcellus Shale production trends. The mapped basement faults fall into two classifications: (1) those faults that are strike parallel to the basin and related to the Rome trough and (2) those faults that trend perpendicular to the strike of the basin and are interpreted as transform faults or cross-strike structural discontinuities (CSDs).<ref name=H&L1987>Harper, J. A., and C. D. Laughrey, 1987, Geology of the oil and gas fields of southwestern Pennsylvania: Commonwealth of Pennsylvania Mineral Resource Report 87, p. 91–97.</ref> These basement faults represent zones of weakness believed to have been reactivated several times during the Paleozoic (Negus-DeWyss, 1979; Lee, 1980; Shumaker, 1993). In addition, reactivation caused significant structural inversion in some areas. It is likely that movement along these faults has continued well into the Quaternary, as the surface expression of several of these major features are clearly apparent on both topographic maps and satellite images.

The Rome trough is a prominent structural feature of the Appalachian Basin, representing a failed rift system formed in the Middle Cambrian. The Rome trough has been extensively studied in West Virginia and eastern Kentucky, and it extends into Pennsylvania and New York (Harper and Laughrey, 1987; Shumaker, 1996; <ref>Scanlin, M. A., and T. Engelder, 2003, The basement versus the no-basement hypothesis for folding within the Appalachian Plateau Detachment Sheet: American Journal of Science, v. 303, 519–563 p.</ref>; Kulander and Ryder, 2005). Shumaker (1993) showed several areas where the Rome trough affected sedimentation of key Devonian organic shale members and also where reactivation of basement faults provided for enhanced areas of natural fracturing in the Cottageville and Midway Extra Shale fields in West Virginia. These basement faults are well documented to have been active during the Late Devonian, affecting deposition of reservoir sands along Rome trough-bounding faults in West Virginia and Pennsylvania (Boswell, 1985; Harper and Laughrey, 1987; Murin, 1988; Flaherty, 1994). Closer to the emerging Marcellus Shale play, Kulander and Ryder (2005) defined the boundaries of the Rome trough in southwestern Pennsylvania through a series of regional cross sections and regional seismic profiles. The Rome trough appears to delineate areas of maximum deposition of key organic shale beds in the Marcellus Shale as well as overlying beds such as the Tully Limestone. In addition, it is a critical feature related to both the burial and thermal maturity history of the Marcellus Shale.

The Rome trough is a prominent structural feature of the Appalachian Basin, representing a failed rift system formed in the Middle Cambrian. The Rome trough has been extensively studied in West Virginia and eastern Kentucky, and it extends into Pennsylvania and New York (<ref name=H&L1987 />; Shumaker, 1996; <ref>Scanlin, M. A., and T. Engelder, 2003, The basement versus the no-basement hypothesis for folding within the Appalachian Plateau Detachment Sheet: American Journal of Science, v. 303, 519–563 p.</ref>; Kulander and Ryder, 2005). Shumaker (1993) showed several areas where the Rome trough affected sedimentation of key Devonian organic shale members and also where reactivation of basement faults provided for enhanced areas of natural fracturing in the Cottageville and Midway Extra Shale fields in West Virginia. These basement faults are well documented to have been active during the Late Devonian, affecting deposition of reservoir sands along Rome trough-bounding faults in West Virginia and Pennsylvania (Boswell, 1985; <ref name=H&L1987 />; Murin, 1988; Flaherty, 1994). Closer to the emerging Marcellus Shale play, Kulander and Ryder (2005) defined the boundaries of the Rome trough in southwestern Pennsylvania through a series of regional cross sections and regional seismic profiles. The Rome trough appears to delineate areas of maximum deposition of key organic shale beds in the Marcellus Shale as well as overlying beds such as the Tully Limestone. In addition, it is a critical feature related to both the burial and thermal maturity history of the Marcellus Shale.

Offsetting the Rome trough strike-parallel basement faults are a series of cross-striking basement faults, which are likely transform faults created during rifting episodes in the Cambrian and Ordovician (Harper and Laughrey, 1987). These faults experienced several subsequent episodes of reactivation. The faults have been identified based on lineament studies, remote-sensing analysis, surface drainage patterns, and structural mapping. The surface expressions of these strike-normal faults were termed cross-strike structural discontinuities by Wheeler (1980). The two most significant are the Tyrone-Mt. Union lineament (Canich and Gold, 1977; Rodgers and Anderson, 1984) and the Pittsburgh-Washington lineament (Lavin et al., 1982). Rodgers and Anderson (1984) reported that an increase in natural fracturing and also enhanced hydrocarbon and fluid migration occurred along the Tyrone-Mt. Union lineament.

Offsetting the Rome trough strike-parallel basement faults are a series of cross-striking basement faults, which are likely transform faults created during rifting episodes in the Cambrian and Ordovician.<ref name=H&L1987 /> These faults experienced several subsequent episodes of reactivation. The faults have been identified based on lineament studies, remote-sensing analysis, surface drainage patterns, and structural mapping. The surface expressions of these strike-normal faults were termed cross-strike structural discontinuities by Wheeler (1980). The two most significant are the Tyrone-Mt. Union lineament (Canich and Gold, 1977; Rodgers and Anderson, 1984) and the Pittsburgh-Washington lineament (Lavin et al., 1982). Rodgers and Anderson (1984) reported that an increase in natural fracturing and also enhanced hydrocarbon and fluid migration occurred along the Tyrone-Mt. Union lineament.

Within the Appalachian Basin, these features have a significant and typically detrimental effect on oil and gas production from many reservoirs, including the Lower Devonian Oriskany/Chert, Upper Devonian sands, Silurian Medina reservoirs, and the Ordovician Rose Run Sandstone reservoirs, with field terminations occurring at or near the cross-strike features. The effects that CSDs may have on Marcellus Shale production is not fully known at this time. However, it should be noted that one of the major Marcellus development projects to date is the Range Resource Washington County project, which straddles the Pittsburgh-Washington lineament.

Within the Appalachian Basin, these features have a significant and typically detrimental effect on oil and gas production from many reservoirs, including the Lower Devonian Oriskany/Chert, Upper Devonian sands, Silurian Medina reservoirs, and the Ordovician Rose Run Sandstone reservoirs, with field terminations occurring at or near the cross-strike features. The effects that CSDs may have on Marcellus Shale production is not fully known at this time. However, it should be noted that one of the major Marcellus development projects to date is the Range Resource Washington County project, which straddles the Pittsburgh-Washington lineament.

* Gwinn, V. E., 1964, Thin-skinned tectonics in the Plateau and northwestern Valley and Ridge provinces of the central Appalachians: Geological Society of America Bulletin, v. 75, no. 9, p. 863–900, doi:10.1130/0016-7606(1964)75[863:TTITPA]2.0.CO;2.

* Gwinn, V. E., 1964, Thin-skinned tectonics in the Plateau and northwestern Valley and Ridge provinces of the central Appalachians: Geological Society of America Bulletin, v. 75, no. 9, p. 863–900, doi:10.1130/0016-7606(1964)75[863:TTITPA]2.0.CO;2.

* Hamilton-Smith, T., 1993, Stratigraphic effects of the Acadian orogeny in the autochthonous Appalachian Basin, in D. C. Roy and J. W. Skehan, eds., The Acadian orogeny: Recent studies in New England, Maritime Canada, and the authochthonous foreland: Geological Society of America Special Paper 275, p. 153–164.

* Hamilton-Smith, T., 1993, Stratigraphic effects of the Acadian orogeny in the autochthonous Appalachian Basin, in D. C. Roy and J. W. Skehan, eds., The Acadian orogeny: Recent studies in New England, Maritime Canada, and the authochthonous foreland: Geological Society of America Special Paper 275, p. 153–164.

* Harper, J. A., 2008, The Marcellus Shale: An old “new” gas reservoir in Pennsylvania: Pennsylvania Geology, v. 38, no. 1, p. 2–13.

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* Harper, J. A., and C. D. Laughrey, 1987, Geology of the oil and gas fields of southwestern Pennsylvania: Commonwealth of Pennsylvania Mineral Resource Report 87, p. 91–97.

*  

* Heidbach, O., M. Tingay, A. Barth, J. Reinecker, D. Kurfebeta, and B. Muller, 2008, The world stress map based on the database release 2008, equitorial scale 1:46,000,000: Paris, Commission for the Geological Map of the World, doi:10.1594/GFZ.WSM.Map2009, 2009.

* Heidbach, O., M. Tingay, A. Barth, J. Reinecker, D. Kurfebeta, and B. Muller, 2008, The world stress map based on the database release 2008, equitorial scale 1:46,000,000: Paris, Commission for the Geological Map of the World, doi:10.1594/GFZ.WSM.Map2009, 2009.

* Jarvie, D. M., R. J. Hill, and R. M. Pollastro, 2005, Assessment of the gas potential and yields from shales: The Barnett Shale model, in Unconventional energy resources in the southern midcontinent, 2004 symposium: Oklahoma Geological Survey Circular 110, p. 37–50.

* Jarvie, D. M., R. J. Hill, and R. M. Pollastro, 2005, Assessment of the gas potential and yields from shales: The Barnett Shale model, in Unconventional energy resources in the southern midcontinent, 2004 symposium: Oklahoma Geological Survey Circular 110, p. 37–50.

* Murin, T. M., 1988, Sedimentology and structure of the First Bradford Sandstone in the Pennsylvania plateau province: Master's thesis, University of Pittsburgh, Pittsburgh, Pennsylvania, 95 p.

* Murin, T. M., 1988, Sedimentology and structure of the First Bradford Sandstone in the Pennsylvania plateau province: Master's thesis, University of Pittsburgh, Pittsburgh, Pennsylvania, 95 p.

* Murphy, A. E., 2000, Physical and biochemical mechanisms of black shale deposition, and their implications for ecological and evolutionary change in the Devonian Appalachian basin: Ph.D. dissertation, Northwestern University, Evanston, Illinois, 363 p.

* Murphy, A. E., 2000, Physical and biochemical mechanisms of black shale deposition, and their implications for ecological and evolutionary change in the Devonian Appalachian basin: Ph.D. dissertation, Northwestern University, Evanston, Illinois, 363 p.

* National Energy Technology Laboratory, 2007, Archive of unconventional gas resources program: http://www.netl.doe.gov/publications/cdordering.html (accessed August 1, 2010).

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* Negus-deWyss, J., 1979, The eastern Kentucky gas field: A geological study of the relationship of oil shale gas occurrence to structure, stratigraphy, lithology, and inorganic geochemical parameters: Ph.D. dissertation, West Virginia University, Morgantown, West Virginia, 199 p.

* Negus-deWyss, J., 1979, The eastern Kentucky gas field: A geological study of the relationship of oil shale gas occurrence to structure, stratigraphy, lithology, and inorganic geochemical parameters: Ph.D. dissertation, West Virginia University, Morgantown, West Virginia, 199 p.

* Nyahay, R., J. Leone, L. B. Smith, J. P. Martin, D. J. Jarvie, 2007, Update on regional assessment of gas potential in the Devonian Marcellus and Ordovician Utica shales of New York: Search and Discovery Article 10136: http://www.searchanddiscovery.com/documents/2007/07101nyahay/#05 (accessed October 9, 2009).

* Nyahay, R., J. Leone, L. B. Smith, J. P. Martin, D. J. Jarvie, 2007, Update on regional assessment of gas potential in the Devonian Marcellus and Ordovician Utica shales of New York: Search and Discovery Article 10136: http://www.searchanddiscovery.com/documents/2007/07101nyahay/#05 (accessed October 9, 2009).