Discussion on Dynamic Reserves Estimation of Multilayer Gas Reservoir With Material Balance Method

Abstract In recent years, more and more multilayer gas reservoirs were discovered in the world. Forecasting the dynamic reserve of multilayer producer is a major challenge for reservoir engineering. Material Balance Equation (p/z plot) is one of the fundamental methods for reserve estimation. It is usually used in single layer gas reservoir. In this paper, the applicability of multilayer gas reservoir material balance equation for reserve estimation is studied by single well numerical simulation. There are several parameters which influence reserve estimation of multilayer gas reservoir, such as the connectivity between layers of gas reservoir, the difference between formation pressures of the layers, the difference between permeability of the layers. Results of numerical simulation show that vertical permeability is the main factor that influences reserve estimation. Reserve estimation has a large accuracy when vertical permeability is larger than 1E-4mD. Reserve estimation value tends to be smaller than the true value when the vertical permeability is smaller than 1E-4mD, and the more non-homogeneous layer, the larger the deviation is. The results of numerical simulation show that difference between the permeability of the layers is another main factor in reserve estimation. For a larger non-homogeneity between layers, calculated dynamic reserve decreases as increase of non-homogeneity between layers, and the dynamic reserve of the layer with low permeability is low.