Effect of Structural Deformation on the Petrology and Distribution of Diagenetic Alteration within the Oriskany Sandstone in Little Mountain Anticline of the Smoke Hole Region of Eastern West Virginia

Abstract

The Lower Devonian Oriskany Sandstone is a quartz arenite formation that is located throughout the Appalachian Basin and extends from New York to Virginia. In West Virginia, Oriskany Sandstone found in the western and central part of the state possesses favorable reservoir porosity values of ~6% and permeability values of ~10md. In the structurally complex northeastern part of West Virginia, the Oriskany Sandstone contains much lower porosity and permeability values due to diagenetic alteration. This study focuses on identifying the diagenetic alterations that create and destroy porosity in northeast West Virginia Oriskany Sandstone. An Oriskany Sandstone bed, located in Little Mountain Anticline of the Smoke Hole Region in northeast West Virginia, was divided into three fold zones and analyzed through thin section. Petrographic and diagenetic analysis was accomplished by using the 300 point count method on samples in thin section. Mineralogically the sandstone contains 63% quartz, 23% feldspar, 7% carbonate, 5% argillaceous and accessory minerals, and the remainder was porosity. Porosity occluding diagenetic alterations observed in Little Mountain Anticline include cementation by quartz, feldspar, and carbonate. All microscopic primary porosity was occluded. Secondary porosity ([less than] 2%) is associated with grain dissolution and the formation of solution seams and stylolites. Solution seams and stylolites are oriented parallel to bedding, having formed due to overburden stresses, and at acute angles to bedding, resulting from deformational stresses. Porosity differs between zones. South limb and axis zones show dissolution and solution seam-related porosity whereas the north limb zone shows only solution seam-related porosity. These microscopic-scale properties are not favorable for natural gas extraction, and unsuitable for potential future CO2 sequestration.