Lateral Continuity of Stochastic Shale Barriers

Abstract

Characterizing shale barriers in oilsands reservoirs is of critical importance for recovery predictions. High net to gross reservoirs contain small shale intervals that impede vertical drainage and have a large impact on recovery. The information on reservoir and shale interval thicknesses collected from vertical delineation wells provide only limited information about the horizontal extent and connectivity of these intervals. The main challenge is that often, such flow barriers cannot be correctly characterized due to the large spacing of delineation wells; the shales are laterally too small to be correlated between wells. Stochastic shales' characteristics are a strong function of their depositional environment (Harris, 1975). Over the past few decades, a significant amount of stratigraphic literature on the nature and character of mud beds in fluvial and tidal settings has been published (Galloway and Hobday, 1996; Miall, 1996). However, the detailed geometry and structure of remnant shales in dominantly sandy sediments is not well documented which motivates studies such as this. This paper proposes a novel methodology based on an inverse modeling scheme to estimate the lateral extent of shales independent of the gridding system. The paper includes a description of the methodology and a case study with implementation details and validation steps.