Practical Considerations in Estimating Test Duration for Perforation Inflow Tests

Abstract

Abstract Perforation inflow tests are short, cost-effective and environmentally- friendly solutions to estimate the initial reservoir pressure, permeability and skin, immediately after perforating the well. The reservoir-dominated (radial) flow regime must be reached before terminating the test in order to obtain reasonable estimates of these parameters. These reservoir parameters and chamber (or wellbore) volume directly influence the rate of build-up of pressure and the test duration. In the field, it is not easy to ascertain whether or not sufficient data has been obtained so that the test can be terminated, especially when the data is not analyzed in real time. If the rate of build-up is closely monitored, it is possible to predict whether (i) the minimum required data will be obtained within the stipulated test time, (ii) the test has to be run longer, or (iii) a downhole shut-in is required. In this paper, analytical simulation is used to run a sensitivity study on reservoir and well parameters and see how these affect the onset of the reservoir-dominated flow regime. The impulse derivative is used to identify the presence of reservoir-dominated flow. The rate of pressure build-up at I hour is used to determine if sufficient data will be collected within the test duration. The outcome is a practical field guide to help the operator decide whether the test should be continued, modified or stopped. Introduction Perforation inflow tests are short and therefore increasingly popular in the industry. They can deliver valuable reservoir information, such as the initial reservoir pressure, the reservoir permeability and the skin effect. The data obtained from perforation inflow tests can be divided into two parts:the early-time data is wellbore storage dominated, andthe late-time data is reservoir- dominated. Perforation inflow tests are not likely to exceed approximately 24 hours, and should be designed so that reservoir-dominated flow occurs during that period. For cases where wellbore storage does not excessively affect the early time data and when reservoir permeability is high enough, the duration of the perforation inflow test is likely sufficient to reach radial flow. However, for large wellbore storage and low reservoir permeability, the time to reach reservoir- dominated flow will be prohibitively long. In such cases, one option is to reduce wellbore storage by running a bridge plug, thus reducing the effects that initially masked the true reservoir performance.