Use of Transient Data to Calculate Absolute Permeability and Average Fluid Saturations

Abstract

Abstract A new well testing analysis method is presented. The method allows for calculating the absolute permeability of the formation in the area influenced by the test and the average saturations in this area. The method applies to two-phase flow in the reservoir (oil and water or oil and gas). Future expansion to three-phase flow is possible. Current analysis methods yield only the effective permeability for the dominant flowing phase and the "total mobility" of all phases. The new method uses the surface flow rates and fluid properties of the flowing phases and the same relative permeability relations used in characterizing the reservoir and predicting its future performance. The method has been verified by comparing the results from analyzing several synthetic tests that were produced by a numerical simulator with the input values. Use of the method with field data is also described. The new method could be applied wherever values of absolute permeability or fluids saturations are used in predicting well and reservoir performance. Probably the major impact would be in reservoir simulation studies where the need to transform well testing permeability to simulator input values is eliminated and an additional parameter (fluids saturations) becomes available to help history match the reservoir performance. This work will also help in predicting well flow rates and where absolute permeability changes with time (e.g., from compaction). Results showed that the values of absolute permeability in water-oil cases could be reproduced within 3% of the correct values and within 5% of the correct values in gas-oil cases. Errors in calculating the fluid saturations were even less. One of the main advantages of this method is that the relative permeability curves used in calculating the results and later on in using the results are the same ensuring consistent process. The impact of this study will be to expand the use of the information already contained in transient data and surface flow rates of all phases. The results will provide engineers with additional parameters to improve and speed up the prediction of well and reservoir performances in just about all studies.