HOHN, MICHAEL ED, and RONALD R. McDOWELL, West Virginia Geological and Economic Survey, Morgantown, WV

ABSTRACT: Geostatistical Simulation of Reservoir Heterogeneity in a Lower Mississippian Sandstone, Appalachian Basin

Since the discovery of the Mount Morris (Pennsylvania) field in 1886, oil and gas have been produced from the lower Mississippian, Big Injun sandstone in approximately 40 fields in northern and central West Virginia and southern Pennsylvania. Big Injun oil fields are noted for poor success in offset drilling and difficulty in water flooding. As part of a study of Big Injun heterogeneity in the Granny Creek field in West Virginia, geostatistical techniques have been used to simulate reservoir properties.

Available data include initial potential, cumulative production, porosity and permeability from core plugs, and porosity computed from density logs. Initial potential (IP) data are the least reliable, but are abundant and reflect local permeability. Variography and indicator kriging of IP's for Granny Creek show highs arranged in a narrow N-S trend and in a second, broad NW-SE trend. Indicator variograms of ten-year cumulative production show a distinct N-S anisotropy for cutoffs at or below the median. This anisotropy is attenuated at higher rates of production, and, above the median, becomes sub-parallel to the NW-SE trend in IP's. Conditional simulation using the sequential indicator algorithm illustrates a high level of uncertainty, and heterogeneity ranging from field scale to th scale of individual well pairs.

Porosity and permeability data taken from cores and geophysical logs are problematic because of the different sources. A Markov-Bayes approach was used to derive conditional simulations of porosity and permeability allowing direct comparison with production trends. Geostatistical simulation highlights areas of high calculated original oil in place (OOIP) as well as low cumulative production.

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