Determining structural and stratigraphic controls on natural gas production of the Upper Devonian Gordon sandstone, Catskill delta complex, southern West Virginia

Abstract

Understanding the controls on natural gas production from the Upper Devonian Gordon sandstone may help petroleum geologists and reservoir engineers better develop and implement a plan for reservoir restimulation to recover addition petroleum resources in southern West Virginia. To test whether the controls are structural, stratigraphic or a combination, downhole geophysical data were obtained from the West Virginia Geologic and Economic Survey. A variety of parameters were used as proxies to determine physical characteristics of the rocks in question: gamma ray, bulk density, and density porosity. Gamma-ray was used as a proxy for lithology to correlate the Gordon sandstone from northern West Virginia into southern West Virginia, to determine thickness and lithology variation within the Gordon interval, thickness and distribution of the Gordon interval that is [greater-than or equal to 50% sand, create cross sections, structure contour maps, and isopach maps. Bulk density was used to calculate the log porosity fraction of the material, and later converted to log porosity percent. Using petrophysical data from Ameri et al. (2001) predicted permeability values were calculated for the Gordon sandstone. Cross-sections illustrate that the Gordon interval is correlative across West Virginia; however, the individual sand bodies that comprise the Gordon are lenticular in shape and non-continuous. Gordon sediments are thickest in the northeast along the Catskill delta complex and thin to the west and southwest in a basinward direction. This is also true for Gordon sediments comprised of >50% sand. However, in the south, there is a NNE-SSW linear trend of thicker more sand-rich sediments than that of adjacent Gordon sediments. The primary tract is located along strike of a slight structural high, that is comprised of a thicker sandy Gordon interval that exhibits higher porosity values (12% - 15%), and permeability values (5mD - 20mD) than adjacent Gordon sediments (6% - 9%; 0.7mD - 3mD respectively). Traditionally in northern West Virginia the Gordon sandstone is defined as marginal marine at the point of maximum regressions in late Devonian time. Analysis of the maps produced for this study indicate that Gordon sediments in southern West Virginia were likely deposited as continental shelf sheet sands south of the Catskill delta complex.