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Estimates of Natural Gas Resources and Recovery Efficiencies Associated with Marcellus Development in Northern West Virginia - Reports of Investigation RI-36

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Evaluation of more than 270 digital well log suites has been conducted to provide a first order estimate of the original in-place natural gas resources associated with the Marcellus and Geneseo-Burket organic-rich shales in West Virginia. It is determined that original gas-in-place (OGIP) resources exceed 40 Bcf/mi2 over much of the State and exceed 150 Bcf/mi2 in northcentral West Virginia. These volumes represent substantial increases from prior estimates, reflecting not only improved data volume and quality, but also the calibration of in-place estimates via comparison to observed and predicted well production. Where input assumptions and parameters are poorly constrained (for example grain density or water saturation), they were set at reasonable values that enable resulting OGIP to exceed expected well recovery at any specific location. A primary contributor to increased OGIP volumes is the shift in focus from assessment of a single given lithostratigraphic unit to broader "Reservoir Units" (RUs). Two RUs are deemed to be present within the current area of shale gas development in northern West Virginia. The Marcellus Reservoir Unit (MRU) includes resources within the Marcellus and bounding formations and is defined to extend upwards to either 300 ft above the top of the Marcellus or to the base of the Tully Limestone where the Tully is judged to be a likely fracture (frac) barrier. A separate Geneseo-Burket Reservoir Unit (GBRU) exists wherever the Geneseo-Burket organic-rich shales are not included within the MRU. The GBRU similarly extends upwards 300 ft from the top of the Geneseo-Burket. At present, only the MRU has been a target of significant development using modern horizontal drilling and hydraulic fracturing methods. Additional RUs associated with the Rhinestreet Shale and the Huron Member of the Ohio Shale are present in parts of West Virginia but are not assessed in this report.
Total OGIP resources are estimated at 878 Tcf for the MRU and 115 Tcf for the GBRU. Stratigraphically, 532 Tcf is assigned to the Marcellus Formation, with additional substantial volumes in overlying formations including the Mahantango (125 Tcf) primarily in the northeastern portion of the State, along with the Genesee-Harrell (281 Tcf) and Sonyea (122 Tcf) in the northcentral and northwestern areas. Primary controls on resources are the thickness and organic-richness of the units and distribution of overpressure. In-place resource density is observed to vary significantly within each RU. Within the MRU, strongly-delineated northeast-to-southwest trends of in-place resources correlate well with increased thickness, porosity, and organic-richness of the various units, with likely connection to known basement structures. The study OGIP/mi2 estimates for the MRU are compared with previously reported estimates of technically recoverable resource density (TRR/mi2) to provide an initial estimate of the scale and variation in potential ultimate recovery efficiency (RE) associated with ongoing Marcellus development. It is estimated that RE likely exceeds 50% within the core of the play and declines to less than 10% along the play margins.
Page last revised April 1, 2021.
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