ABSTRACT: Reservoir Sedimentology and Petrophysical Heterogeneity of Big Injun Sandstone of West Virginia

ZOU, XIANGDONG, ALAN C. DONALDSON, RICHARD SMOSNA, and KATHY R. BRUNER, West Virginia University, Morgantown, WV

Based on the analysis of geophysical logs and cores from closely spaced wells, the lower Big Injun sandstone of Granny Creek oil field is identified as a fluvial-deltaic deposit. Abundant lateral and vertical heterogeneities are related to sedimentation and diagenetic controls. It consists of two distinctive lithologies throughout the fields: fine-grained sandstones overlain by pebbly and coarse-grained sandstones.

The lower fine-grained litharenites and sublitharenites are of distributary-mouth bars. Stratigraphic cross sections using geophysical logs show this delta-front deposit as three laterally accreting sandstones that are partitioned by intertonguing shales, providing evidence of a southwestward prograding shoreline. Subfacies include (1) distal mouth bar: very fine-grained sandstone, shaly and organic rich; (2) marine-influenced proximal mouth bar: fine-grained sandstone,

texturally mature, slightly pebbly; and (3) fluvial-influenced proximal mouth bar: interbedded very fine- and coarse-grained sandstones. The principal pay is the marine influenced proximal bar, where porosity ranges from 13 to 23% and permeability, up to 24 md.

Upper coarse-grained part of the reservoir, consisting of quartzarenites and sublitharenites, is fluvial in origin. Subfacies include: (1) channel lag, (2) point bar, and (3) chute fills. Porosity is significantly reduced by cements.

Isopach maps indicate that some high oil production follows the shoreline trend of the mouth-bar sandstones, particularly where overlap of imbricated sandstones occurs. The reservoir is suitable for enhanced oil recovery by water flooding.

AAPG Search and Discovery Article #91013©1992 AAPG Eastern Section Meeting, Champaign, Illinois, September 20-22, 1992 (2009)