Well Test Analysis of Multilayer Edge-Water Gas Reservoirs

Abstract

Because the application of zonation test and multilayer test is rare, the well tests of most multilayer edge-water gas reservoirs are often interpreted with singer layer model, which lead to erroneous analyses. In order to recognize the edge-water and obtain the parameters in multilayer gas reservoirs accurately, a well test model of a vertical well in multilayer edge-water gas reservoirs considering the distinct respective properties and distinct respective distances to edge-water in each layer is established and solved. Type curves of pressure transients are plotted. The effects of distinct properties between layers on the well test type curves with different distance to edge-water are analyzed. The results showed that the effect of edge-water is reflected early on type curves due to the distinct diffusivity between layers. This results in relatively small value of the minimum distance to edge-water which is interpreted with a singer layer model. The greater the different diffusivity between layers the earlier the reflective of edge-water on type curves. The greater the different diffusivity between layers the smaller interpretative value of the minimum distance to edge-water too. Therefore, a well test interpretation method of a vertical well in multilayer edge-water gas reservoirs is proposed which combines the single layer edge-water well test interpretation, multilayer edge-water well test model and the ratio of formation capacity and porosity between layers from well log interpretation. The correct value of minimum distance to edge-water and the approximate permeability of each layer can be obtained by use of the proposed well test interpretation method. Field case buildup analyses of a gas well in multilayer edge-water gas reservoirs show the applicability of the new well test interpretation method.