Marcellus Shale (Devonian) -- Appalachian Basin
By Katherine Schmid, Pennsylvania Geological Survey, Pittsburgh Pennsylvania, USA
The Middle Devonian Marcellus Shale of the Appalachian Basin is the most extensive shale play in the U.S., covering about 66,600,000 acres (USGS Marcellus Shale Assessment Team, 2011). Extending from Tennessee to New York, the gross thickness of the Marcellus Shale increases to the northeast, with the thickest area located in northeastern Pennsylvania (Wrightstone, 2009; Erenpreiss and others, 2011; Wang and Carr, 2013). The organic-rich zone of the Marcellus Shale has a net thickness of 50 to over 400 feet (Erenpreiss and others, 2011), and exists at drilling depths of 2,000 to 9,000 feet measured depth (MD) (Zagorski and others, 2012; Wang and Carr, 2013). The organic-rich Marcellus Shale has high radioactivity responses, and thus high gamma ray values on well logs, because the organic matter tends to concentrate uranium ions (Harper, 2008). According to studies during and after the Eastern Gas Shales Project (EGSP), there is a strong relationship between higher-than-normal gamma ray response and total gas content in the black, organic-rich Marcellus Shale. Published data indicates the total organic carbon content (TOC) of the Marcellus Shale is as high as 11% (Repetski and others, 2008). As reported in Milici and Swezey (2006), Repetski and others (2008), and Ryder and others (2013), analyzed samples of the Marcellus Shale had mean random vitrinite reflectance values between 1.0 and 2.5% in the majority of the currently productive area, where most production has been natural gas and natural gas liquids. However, in southwest Pennsylvania, eastern Ohio, and northern West Virginia, reported production included condensate and oil from wells in the Marcellus Shale.
In October 2019, the U.S. Geological Survey (USGS) published Fact Sheet 2019-3050, “Assessment of undiscovered gas resources in the Middle Devonian Marcellus Shale of the Appalachian Basin Province, 2019” (Higley and others, 2019). This fact sheet divided the Marcellus up into six different assessment units. According to this publication, the USGS estimated a mean undiscovered, technically recoverable natural gas resource of about 96 tcf and a mean undiscovered, technically recoverable natural gas liquids resource of 1.5 billion bbls in continuous-type accumulations in the Marcellus Shale. The estimate of natural gas resources ranged from 34 to 181 tcf (95 percent to 5 percent probability, respectively), and the estimate of NGL resources ranged from 0.5 to 3.02 billion bbls (95 percent to 5 percent probability, respectively).
The USGS estimates are for resources that are recoverable using currently available technology and industry practices, regardless of economic considerations or accessibility conditions, such as areas limited by policy and regulations. These Marcellus Shale assessment covered areas in Kentucky, Maryland, New York, Ohio, Pennsylvania, Tennessee, Virginia, and West Virginia. After evaluating production for over 6,000 Marcellus and Utica wells, Boswell (2021) says that these federal assessments “substantially understate available resources” (p. 2). One possible explanation for this is that water saturations used in these assessments are overestimated (Blood, et al., 2020). While examining production in the core areas of the Marcellus shale play, Boswell (2021) observed that cumulative well production per square mile exceeded predictions from USGS and EIA assessments. Boswell (2021) calculates that the ultimate technically recoverable resources is 873 tcf for the Marcellus shale play.
Maryland:
According to the Maryland Geological Survey (MGS), the Marcellus Shale is present in Garrett and Allegany counties in western Maryland, where its thickness is 150 to 250 feet (Brezinski, 2010, 2011). The depth of the Marcellus Shale in western Maryland is zero to more than 8,000 feet MD (Brezinski, 2010, 2011). There is currently (2020) no production from the Marcellus Shale in Maryland. There were no exploration wells drilled to the Marcellus Shale in Maryland between 1996 and 2020. Due to the estimated thermal maturity of the Marcellus Shale in Maryland (Repetski and others, 2008), it is likely that dry gas will be found if wells are drilled and completed in the Marcellus Shale. There is currently a moratorium on drilling unconventional wells in Maryland.
New York:
The Marcellus Shale extends into the northernmost part of the Appalachian basin in central New York. The organic-rich thickness of the Marcellus Shale increases from 20 feet in the west to 250 feet in the eastern part of the basin in New York (Smith and Leone, 2010). The depths of the Marcellus Shale range from zero to as much as 7,000 feet MD in the eastern part of the basin in south-central New York (Smith and Leone, 2010). According to the New York State Department of Environmental Conservation (DEC), 50 vertical wells have been drilled that reported Marcellus Shale as a producing formation. Of those, 14 were listed as active in 2019. Production reported from the Marcellus Shale from the 14 active wells in 2019 (most recent data available) was 17.9 Mcf of gas, down from the high of 64 Mcf reported for 2008. There was no reported oil or condensate production. In 2019, most of the productive wells were located in Steuben County, with some also in Allegany, Chautauqua, Chemung, Livingston, an Wyoming counties. According to the DEC, there were over 350 Mcf of gas produced from the Marcellus Shale between 2000 and 2019. The DEC also reported that between 1967 and 1999, there may have been as much as 543 Mcf of gas produced from the Marcellus Shale.
At the conclusion of a seven-year study of the environmental impact of high-volume hydraulic fracturing (HVHF), the New York DEC published the Final Supplemental Generic Environmental Impact Statement (SGEIS) in April, 2015; it is available at http://www.dec.ny.gov/energy/75370.html. On June 29, 2015, the State Environmental Quality Review (SEQR) Findings Statement for HVHF was issued by the DEC Commissioner (available at http://www.dec.ny.gov/docs/materials_minerals_pdf/findingstatehvhf62015.pdf), which officially prohibits HVHF in New York.
Ohio:
Based on completion reports from the Ohio Department of Natural Resources (DNR), over 27.3 bcf of gas and 972,000 bbls of condensate and/or oil were produced from the Marcellus Shale from 2007 through 2020 (most recent data available). There were 24 wells that reported production from the Marcellus Shale in 2020. According to the DNR completion reports, there were about 5.8 bcf of gas and about 122,000 bbls of oil and/or condensate produced in 2020. The Marcellus Shale wells reported as active were in Athens, Belmont, Jefferson, Meigs, Monroe, Noble, and Washington counties.
The maximum thickness of the Marcellus Shale in Ohio is about 75 feet, but generally the Marcellus Shale is 30-50 feet thick in the productive area in eastern Ohio (Erenpreiss and others, 2011). The depth to the base of the Marcellus Shale in the productive area in eastern Ohio is 2,500-5,000 feet MD (Wickstrom and others, 2011). According to Repetski and others (2008), the Marcellus Shale is in the oil-thermal maturity window in eastern Ohio.
Pennsylvania:
The Marcellus Shale is deepest in north-central Pennsylvania, and the deepest well is in Lycoming County and has a true vertical depth of 9,088 feet. The Olympus Energy Midas 6M well in southwestern Pennsylvania was drilled a record-breaking lateral length of 20,060 ft (Boyer, 2021, Gough, 2020). The organic-rich, high gamma ray portion of the Marcellus Shale is thickest in southwestern and north-central Pennsylvania (Perry and Wickstrom, 2010; Harper, 2008), reaching over 400 feet thick in Susquehanna and Wyoming counties (Erenpreiss and others, 2011). Pennsylvania has continued to be the state with the most gas production from the Marcellus Shale. In 2020, according to the Pennsylvania Department of Conservation and Natural Resources (DCNR) and Department of Environmental Protection (DEP), the areas of greatest drilling activity in the Marcellus Shale continued to be in southwestern and northeastern Pennsylvania. According to the Pennsylvania DCNR and DEP, the county with the most gas production in 2020 from the Marcellus Shale was Susquehanna County. After Susquehanna, the other counties with the most natural gas production in 2020 were Bradford, Washington, Greene, Lycoming, and Tioga. The counties with the most condensate production in 2020 from the Marcellus Shale were Washington and Butler. Forest County reported the most oil production from the Marcellus Shale in 2020 followed by Washington County.
According to DCNR and DEP, by the end of 2020, about 7,220 wells reported production from the Marcellus Shale, with most production from horizontal wells. Almost 3.2 tcf of gas, about 1.6 million bbls of condensate and 731 bbls of oil were produced from the Marcellus Shale in 2020. In 2020, the largest producers of natural gas from the Marcellus Shale were Cabot Oil & Gas Corporation, Chesapeake Appalachia LLC, SWN (Southwestern Energy) Production Company LLC, Range Resources Appalachia LLC, and Chief Oil & Gas LLC. Range Resources was the largest producer of condensate from the Marcellus Shale in 2020. Tennessee:
According to de Witt and others (1993), the Marcellus Shale is present in the subsurface in northeastern Tennessee. Therefore, in 2011, the USGS determined that the Foldbelt Marcellus Assessment Unit extended into Tennessee (Figure 1). According to the Tennessee Department of Environment and Conservation, Division of Water Resources, Oil and Gas Section, there is no production from the Marcellus Shale in Tennessee.
Virginia:
According to the Virginia Division of Gas & Oil (DGO), there were no wells drilled exclusively for the Marcellus Shale in Virginia between 2004 and 2018. It is possible that natural gas was produced from the Marcellus Shale co-mingled with other zones in vertical wells, but the quantity is unknown. According to Ryder and others (2015), the Marcellus Shale is present but thin in southwest Virginia. Erenpreiss and others (2011) and Wang and Carr (2013) indicate the Marcellus Shale is less than 50 feet thick in southwest Virginia.
West Virginia:
West Virginia is second to Pennsylvania in cumulative production of natural gas from the Marcellus Shale. According to the West Virginia Geological & Economic Survey (WVGES), the first production reported from a horizontal well completed in the Marcellus Shale in West Virginia was in 2007. From 2007 through 2020, about 10.6 tcf of gas were produced from horizontal wells completed in the Marcellus Shale, as well as about 72.7 million bbls of oil and/or condensate, and about 194.4 million bbls of NGL. According to the WVGES, there was reported production from the Marcellus Shale in 2,230 horizontal wells in 2020. In 2020, there were about 17.7 million bbls of oil and/or condensate, almost 57.7 million bbls of NGL, and about 2.1 tcf of gas produced from the Marcellus Shale in horizontal wells.
In 2019, the companies that reported the most gas production from the Marcellus Shale were Antero Resources Corporation, Southwestern Prod Co., EQT Production Co., Northeast Natural Energy, and HG Energy, Inc. (Dinterman, 2020). The companies reporting the most liquids production from the Marcellus Shale in 2019 were Southwestern Production Co., Antero Resources Corp., Tug Hill Operating, Jay-Bee Oil and Gas, and HG Energy LLC. (Dinterman, 2020).
In 2019, the counties from which most of the liquids were produced from the Marcellus Shale were Tyler, Marshall, Ohio, Brooke, and Ritchie (Dinterman, 2020). The counties from which most of the natural gas was produced were Tyler, Doddridge, Ritchie, Ohio, and Marshall (Dinterman, 2020).
In the area where there is Marcellus Shale production in West Virginia, the thickness of the Marcellus Shale is 30 to 120 feet, according to WVGES. The depth to the base of the Marcellus Shale ranges from about 4,000 feet MD in Brooke and Jackson Counties to about 7,000 feet MD in Taylor and Preston Counties. According to Moore and others (2015), in northern West Virginia, the total organic carbon (TOC) content is generally 10% or greater, and reservoir pressures range from 0.3 to 0.7 psi/foot.
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