Fieldwide Determination of Directional Permeabilities Using Transient Well Testing

Abstract

Summary We present here a practical method for estimating the directional permeabilities in anisotropic reservoirs. 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 injector/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 to provide fieldwide permeability distribution at well-spacing scale, which is relevant for estimating fluid 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 straightforward 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 test 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 Field, a carbonate field in Kazakhstan. Of the 12 wells, 10 have interwell tests at three different directions, which 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 that 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 interpretation. However, they differ in other areas, emphasizing the need for using dynamic measurements at well-spacing scale for better understanding of fracture distributions/orientations and their effects on flow communication 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 fieldwide 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 petrophysical analyses reduces uncertainty in reservoir characterization. This method has already been implemented in some commercial well-test-analysis software.