ZOU, XIANGDONG, ALAN C. DONALDSON, and KURT DONALDSON, West Virginia University, Department of Geology and Geography, Morgantown, WV

ABSTRACT: Reservoir Heterogeneity of Big Injun Sandstone in West Virginia: Stratigraphic (Including Diagenesis) Controls on Oil Production in Granny Creek Field

Big Injun sandstone (Price/Pocono Formation, Lower Mississippian), of fluvial-deltaic origin, is a heterogeneous oil reservoir in combination trap of Granny Creek field (WV); compartmentalized by stratigraphy, diagenetic facies, and structural features. Two distinctive lithologies of Big Injun sandstone serve as reservoir and seal respectively: (1) lower fine-grained sandstones (reservoir) of C member deposited in westward prograding river-mouth bars with marine-influenced proximal bars as principal pays (porosity: 13-23%; permeability: up to 24 md); compared with (2) upper coarse-grained sandstone (B and A members) of fluvial bedload origin; consisting of relatively impermeable quartz-cemented B member at its base, which probably is major seal except where eroded away in the northeas ern part of field by the pre-Greenbrier unconformity.

Primary initial and cumulative oil production data show two major trends in the field: (1) N/S orientation, which is also thickness trend of tongues of C member; and (2) NW-SE orientation, which is parallel to erosive edge of Big Injun by pre-Greenbrier unconformity. Those trends consist of intermittent high-production areas of approximately 1000 x 1500 x 15 ft dimensions, which separated by some NE-SW features. Major stratigraphic controls on oil production are position, geometry, trend and distribution pattern of permeable proximal bar subfacies in relationship to (1) B member seal, (2) Pre-Greenbrier unconformity, and (3) partial barriers including (A) thin shaly beds between prograding tongues, and (B) inclined thin intervals, cutting across C member tongues, of diagenetic origin. These partial barriers separate the proximal mouth-bar subfacies into compartments. Rome trough and West Virginia dome were growing structures.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.