HETEROGENEITY OF FLUVIAL-DELTAIC RESERVOIRS IN THE APPALACHIAN BASIN - A CASE-STUDY FROM A LOWER MISSISSIPPIAN OIL-FIELD IN CENTRAL WEST-VIRGINIA

Since discovery in 1924, Granny Creek field in central West Virginia h as experienced several periods of renewed drilling for oil in a fluvia l-deltaic sandstone in the Lower Mississippian Price Formation. Deposi tional and diagenetic features leading to reservoir heterogeneity incl ude highly variable grain size, thin shale and siltstone beds, and zon es containing large quantities of calcite, siderite, or quartz cement. Electrofacies defined through cluster analysis of wireline log respon ses corresponded approximately to facies observed in core. Three-dimen sional models of porosity computed from density logs showed that zones of relatively high porosity were discontinuous across the field. The regression of core permeability on core porosity is statistically sign ificant, and differs for each electrofacies. Zones of high permeabilit y estimated from porosity and electrofacies tend to be discontinuous a nd aligned roughly north-south. Cumulative oil production varies consi derably between adjacent wells, and corresponds very poorly with trend s in porosity and permeability. Original oil in place, estimated for e ach well from reservoir thickness, porosity water saturation, and an a ssumed value for drainage radius, is highly variable in the southern p art of the field, which is characterized by relatively complex interfi ngering of electrofacies and similar variability in porosity and perme ability.