Assigning Effective Values to Simulator Gridblock Parameters for Heterogeneous Reservoirs

Abstract

Summary: Characterization of heterogeneous reservoirs for simulation studies by use of a statistical component to the reservoir description combined with calculation of effective permeabilities is discussed through a case study of a fluvial reservoir. Inspection of whole core and logs from the Sherwood reservoir revealed that it is extremely heterogeneous, containing short shales embedded in a mixture of sands and silts. A statistical approach was used to quantify the distribution of core-plug porosity and permeability measurements to discriminate between significantly different rock types. A successive rescaling procedure was then adopted in which we first calculated effective values for each rock type from the core-plug data. These results were combined with statistics on the spatial distribution of the rock types to calculate effective values for the nonshale part of each layer. Finally, the effect of the shales on the vertical permeability was incorporated. The resulting anisotropy ratios, on the order of 10-3, were used successfully in black-oil model studies, a good match between the simulator predictions and observed production data being achieved with minimal fine tuning of the model parameters.