Stratigraphy and Petroleum Production of Middle and Upper Devonian Shales, Northwestern West Virginia

Abstract

ABSTRACT Middle and Upper Devonian subsurface rocks in six counties in northwestern West Virginia can be divided into formal units of organic-rich black shales overlain by inorganic gray and greenish-gray shales. The section thickens west-to-east from 2,000 to 4,000 feet, including some fine sandstones and siltstones in the upper part. Drilling since 1980 has discovered several productive intervals in this thick sequence. Generally, younger siltstones and shales down to the Huron Shale produce oil and gas; below the Huron, gas dominates. In map view, three broad oil and gas plays can be related to facies changes and to the Burning Springs Anticline. West of this structure, both organic-rich and inorganic shales produce gas; on and immediately east of the anticline, transitional facies (including black and gray shales, and younger siltstones) produce oil and gas; and farther east, siltstone bundles produce gas and some oil. Thus, completion-zone thickness ranges between 30-2,000 feet, with varied completion techniques. Under a current Gas Research Institute contract, we are seeking possible relations among stratigraphy, completion intervals and techniques, initial potential (IP), and production. Preliminary studies in three counties indicate that gas IPs are highest when three or more formations are completed using nitrogen-fracturing. In one first year production study, the average shale oil well east of the Burning Springs Anticline is short-lived, declining by 95% of IP after one year before leveling off. A similar first year production study for 3 adjacent counties indicated less rapid decline of oil wells located along the Burning Springs Anticline.