THE WELL PERFORMANCE OF NATURALLY FRACTURED LENTICULAR SAND RESERVOIRS

The development of a gas-water three dimensional numerical reservoir simulator is presented. This model accounts for the presence of natural fractures and sand lenses. It is assumed that both natural fractures and sand lenses have random distributions in a reservoir. Therefore, the presence/absence of natural fractures or sand lenses at any particular location in the reservoir can be statistically generated a priori by the Monte Carlo method. A double porosity medium is approximated by an equivalent single porosity medium. Only a single equation for each fluid phase is used to describe fluid flow in this equivalent single porosity medium. The fracture concentration and the sand/shale ratio are known parameters. The model can be used to simulate the behavior of a double porosity medium composed of a heterogeneous anisotropic matrix and a heterogeneous anisotropic fracture.;The resulting governing flow equations are solved by the fully implicit procedure. The corresponding finite difference equations are solved iteratively by using either the Point Successive Over-Relaxation or the Line Successive Over-Relaxation.;The simulator can be used as a single-phase gas simulator and as a two-phase gas-water simulator. The model may be a useful tool in the well testing of naturally fractured lenticular sand reservoirs. It can also be used as a performance prediction tool. For the purpose of model verification, the model is applied to some measured pressure drawdown and pressure build-up data. A resonably good match is obtained. Some hypothetical examples are used to demonstrate other capabilities of the model. According to the observed results, it appears that for non-connecting randomly occurring natural fractures, the degree of fracturing does not significantly influence the well performance, at least for the early times. The observed effect of lenticularity on the well production performance is consistent with the results of previous authors.