Field-Wide Determination of Directional Permeabilities using Transient Well Testing
Authors: Pan Yan , Kamal Medhat , Narr Wayne 
Published: September 2016

A practical method for estimating the directional permeabilities in anisotropic reservoirs is presented. The method uses pressure-transient-analysis results from at least three sets of interference/pulse tests among wells offset at different azimuths. Knowledge of the maximum/minimum permeability directions in anisotropic reservoirs helps to optimize injectors/producer locations, and is important for reservoir management especially under secondary/enhanced recovery of hydrocarbons. The proposed method uses transient-test data rich with dynamic information aiming to provide field-wide permeability distribution in well-spacing scale, which is relevant for estimating fluids movement and recovery. Its application in a carbonate oil-field in Kazakhstan is also discussed.

The proposed method uses well coordinates and multiple sets of analysis results of interwell transient tests through mathematical matrix operations. It is straight-forward to use and works efficiently. The algorithms to calculate directional permeabilities in anisotropic homogeneous reservoirs from interference-tests were first introduced by Ramey 1975 and extended to pulse-tests by Kamal 1983. Our new approach can use the analysis results of any type of interwell transient tests directly in heterogeneous reservoirs. Any valid modern methods can be used to analyze each interwell test, and all analysis results can be integrated to generate the field permeability-tensor map.

The proposed method was validated using synthetic cases. Its application in a large set of multiple-well tests in a naturally fractured reservoir illustrated its practicality and efficiency. Extensive interwell transient data have been collected and analyzed from carefully designed and conducted tests among 12 wells in Korolev (a carbonate field in Kazakhstan). Ten of twelve wells each have interwell tests at three different directions, and that allows the calculation of directional permeabilities. The permeability-tensor map is generated for the entire field and compared with the fracture orientations derived from geological structure and image-log interpretation. Both static and dynamic data resources indicate fracture orientations vary substantially throughout the field. In some areas, the dominant permeability directions from interwell transient data are consistent with those from image-log. However, they differ in other areas emphasizing the need for using dynamic measurements in well-spacing scale for better understanding of fracture distributions/orientations and their impacts on flow communications among wells.

The novelty of this method of estimating directional permeabilities is that it uses well coordinates and analysis results of individual interwell transient tests directly in heterogeneous reservoirs. It is convenient and efficient. It can be easily used to generate a field-wide permeability-tensor map using dynamic transient data. Its application in a large carbonate reservoir demonstrates its practicality even in fields with complex varying anisotropy. Integrating the results from this method with those from geological and petrophysics analyses reduces uncertainty in reservoir characterization.