A NUMERICAL APPROACH FOR PERMEABILITY ESTIMATION IN RADIALLY HETEROGENEOUS RESERVOIRS

Abstract

Analytical solutions are used extensively for pressure transient analysis in radially heterogeneous reservoirs. They are generally used for evaluating variation of reservoir properties along the reservoir radius. However, the available analytical solutions are not sufficiently accurate to determine boundaries of zones. As a result, the interior boundaries of heterogeneous zones are often estimated as a function of the average permeability of zones, which sometimes is a cause of nonunique solutions. As a matter of fact, the skin factor does not provide accurate information about the radius and permeability of an altered zone separately. A new numerical well test procedure is presented in this paper based on the finite element method and a special zonal discretization that utilizes nonlinear regression, which is able to detect the interior boundaries of heterogeneous zones. The results demonstrate that this numerical approach is able to capture the spatial variation of permeability in the radially heterogeneous reservoirs under various boundary conditions. A key advantage of this numerical procedure is quantifying heterogeneity in terms of the radius and permeability of the dissimilar zones, whereas analytical methods generally provide a combination of these parameters.