Type-curve analysis of modified two-rate flow test: A simple yet effective technique to minimize the non-uniqueness of interpretation results

Abstract

Two-rate flow test is widely used in petroleum industry to determine reservoir parameters because its advantage of avoiding the need of shutting in the well. Field practice of hundreds of wells in Changqing Oilfield, China, show that lacking the pressure data before production-rate change period during the two-rate flow test – which is a customary rule in the pressure measurement – is likely to bring about unreasonable interpretation results. In this paper, we extend the three-rate flow test (Selim, 1967) by applying Gringarten-Bourdet type curve analysis method, rather than specialized plot, to analyze the testing pressure behavior. This method, we call it modified two-rate flow (MTRF) technique, is tested by measuring a short period of pressure data for an extra production rate (usually it is designed back to initial stabilized condition to reduce the production losses) based on conventional two-rate flow test. As a result, the total measurement time for the MTRF test is nearly equal to, or slightly longer than, conventional two-rate flow test, and much shorter than three-rate flow test. The mathematical justification of Gringarten-Bourdet type curve that applied in MTRF test is re-derived, and the well test designs for horizontal and multi-fractured horizontal wells are conducted to validate the applicability of the MTRF method. Results show that the results of conventional two-rate flow tests are largely dependent on the initial parameters we set, while the results obtained by MTRF method are very close to the correct values even with different and far away initial values. This new technique not only reserves the same advantages as two-rate technique, but also minimizes the non-uniqueness of the results by add an extra pressure history, thus providing a double-check of the results, like permeability, reservoir pressure, and so on.