Application of Tiab's Technique to Multi-Rate Tests
A. Mongi, D. Tiab · 2000
During a pressure drawdown test, it is quite difficult to hold a constant rate long enough to achieve the test requirements. Any change in rate, if not taken into account, can lead to erroneous results. Also pressure drawdown tests are not suitable in sand producing wells. Pressure buildup tests, in high production wells, are uneconomical because of income loss. For these reasons a multirate test is run instead of buildup or constant rate drawdown tests. The conventional analysis of a multirate test requires a type curve matching technique, which is essentially a trial-and-error procedure.A method is presented to analyze variable rate tests in oil reservoirs. This method, referred to as Tiab's Direct Synthesis. utilizes the characteristic intersection points and slopes of various straight lines from a log-log plot of pressure and pressure derivative data. Direct synthesis technique uses exact analytical solutions to obtain reservoir parameters. The pressure derivative concept is introduced for interpreting multirate tests.The proposed technique is applicable for the interpretation of either continuously changing flowrate tests or a series of constant rate tests. This technique is illustrated by several numerical field examples for oil reservoirs.