Geological Heterogeneity Modeling and Permeability Tensor Calculation for an Unstructured Grid Block

M.Hassanpour, Rahman¹, Oy Leuangthong² (1) School of Mining and Petroleum Engineering, University of Alberta, Edmonton, AB (2) University of Alberta, Edmonton, AB

Heterogeneity in a hydrocarbon reservoir generally refers to the complex spatial distribution of rock properties. Simulation of flow in three dimensional reservoirs involves complex geometry and geology; feeding large, fine scale models of facies and/or petrophysical properties into a flow simulator is computationally expensive and inefficient. The use of unstructured grids permits fine resolution of important features such as fault, channels and deviated wells while saving computational effort far way from wells where a coarser resolution is adequate. This inconsistent scale of grid blocks presents an interesting case where coarse scale blocks may consist of multiple facies and/or subsequences; accounting for connectivity of facies within and between adjacent coarse blocks may impart valuable information with respect to flow prediction. Determination of the upscaled permeability of the inherent heterogeneity within these coarse scale blocks is an important component of forecasting flow performance of an unstructured grid. In these cases, a full permeability tensor arises instead of a diagonal tensor.

This study proposes methodologies to (1) account for geological heterogeneity within and between unstructured grid blocks, and (2) calculate the full permeability tensor for this heterogeneous coarse scale irregular block. For the first task, a conventional indicator kriging and simulation approach is used to simulate connected blocks one at a time, with successively increased conditioning to previously simulated locations. The second task applies a flow-based upscaling method using the high resolution facies model captured by geological modeling in the first phase. The full permeability tensor is calculated for a polygonal unstructured grid and some sensitivities are performed for both tasks.