Characterization of Fluvial Sedimentology for Reservoir Simulation Modeling

Abstract

Summary This paper presents a critical study of a 3D stochastic simulation of a fluvial reservoir and of the transfer of the geological model to a reservoir simulation grid. The stochastic model is conditioned by sand-body thickness and position in wellbores. Geological input parameters—sand-body orientation and width/thickness ratios—are often difficult to determine, and are invariably subject to interpretation. Net/gross ratio (NGR) and sand-body thickness are more easily estimated. Sand-body connectedness varies, depending on the modeling procedure; however, a sedimentary process-related model gives intermediate values for connectedness between the values for a regular packing model and the stochastic model. The geological model is transferred to a reservoir simulation grid by use of transmissibility multipliers and an NGR value for each block. The transfer of data smooths out much of the detailed geological information, and the calculated recovery factors are insensitive to the continuity measured in the geological model. Hence, we propose improvements to the interface between geological and reservoir simulation models. Input for our conditional, statistical, sedimentary, process-related model includes regional geological parameters (rates of subsidence and aggradation and grossly contoured paleotopography) and local values (depth, thickness, and direction and width of sand bodies ascertained from well-test and core analyses). Integration of sedimentological understanding of the reservoir's depositional environment is emphasized.