A Thermal Simulator for Naturally Fractured Reservoirs

Abstract

Abstract Because of the relatively heavy oil (8 − 12° API) encountered in many naturally fractured reservoirs, thermal recovery processes could be viable recovery techniques to produce oil from these reservoirs. To facilitate the simulation of these processes, a simulator to model thermal effects in naturally fractured reservoirs has been developed. The model uses the double porosity concept and is three dimensional, three phase, and compositional. It allows the rock matrix block to be subdivided into a two-dimensional (r−z) grid block in order to study effects of gravity, capillary pressure, and mass and energy transfer between fractures and matrix blocks. The simulator is fully implicit and has a coupled wellbore mathmatical formulation, and simultaneously solves the unknowns for fractures and matrix blocks. An efficient solution procedure is implemented so that the cost of modelling naturally fractured reservoirs is not significantly greater than the cost of conventional single porosity thermal simulation. An example, steam injection into a five-spot pattern, is included to illustrate the significant effects of physical properties and model construction. Oil recovery predictions are sensitive to capillary pressure values, the number of cells used to divide the matrix block, and the size of the matrix blocks.