ABSTRACT: Geostatistical Simulation of Petrophysical Rock Types

MURRAY, CHRISTOPHER J., Stanford University, Stanford, CA

The distribution of petrophysical rock types directly controls the fluid flow properties of a reservoir. This paper presents the spatial modeling and simulation of petrophysical rock types of the Cretaceous Muddy Sandstone at Amos Draw field in the northern Powder River basin of Wyoming. Nine cored wells in the field provided sedimentologic descriptions and petrophysical measurements (porosity and permeability). Geophysical well log data (gamma ray, density, and resistivity logs) were also available for the cored wells. In addition, there were 61 uncored wells for which geophysical well logs alone were available. Cluster analysis and crossplots of the core data were used to identify several petrophysical rock types in the cored wells. Examination of the cores and the production data s owed that those rock types were deposited in depositional environments having different production characteristics. Discriminant function analysis of the well log data was used to determine the probability that data points in the 61 uncored wells belonged to each of the rock types previously identified. Spatial modeling of the distribution of the petrophysical rock types was performed using variogram analysis. The variogram modeling depended heavily on geologic models of the depositional environments of each of the petrophysical rock types. Multiple simulations of the distribution of rock types between the wells were then generated using sequential indicator simulation. The simulations of the lithofacies can be used for the generation of permeability and saturation fields that honor the eologic model for the spatial distribution of the rock types.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)