Subsurface mapping and reservoir analysis of the Upper Devonian Venango and Bradford groups in Westmoreland County, Pennsylvania.

摘要

The Upper Devonian Bradford and Venango groups of southwest Pennsylvania are the principal reservoirs in Westmoreland County. These reservoirs were deposited in several fluvial-deltaic environments as part of the "Catskill delta complex". Although these sandstone units have been actively drilled for many years, uncertainties remain in depositional environments, stratigraphic identification, and correlation in the subsurface. Approximately 135 geophysical logs were correlated, and subsurface maps were generated for the reservoirs. The reservoir units of interest include the Fifth, Bayard, Speechley Stray, Speechley, and Balltown B. By linking geologic parameters to reservoir quality and production, the analysis has provided a better understanding of the reservoirs within the study area. Log analysis and cross plot techniques provided mineral composition changes across the study area. Mineralogical compositions were used to interpret depositional environment. High production rates coincide with thick sandstone lobes and lithology, and are not structurally influenced. It appears that the quartz-rich fluvial-deltaic rocks are the best targets as opposed to carbonate dominated marine rocks. The lower Speechley sequence has the highest potential for natural gas productivity. The lower Speechley sequence was interpreted as a valley-fill estuarine sandstone. The sandstone is vertically and laterally extensive with low water saturation. The Speechley Stray sandstone should also be targeted for natural gas. The lower Speechley sequence was interpreted as a muddy delta front deposited along a shoreline. This sandstone was selected because of the potential for high secondary porosity caused by dissolution of calcite.