A new look at the minimum miscibility pressure (MMP) determination from slimtube measurements

Slimtube measurement is one of the standard experimental techniques used for determining the minimum miscibility pressure (MMP) of an oil and injection gas system prior to the initiation of an enhanced oil recovery (EOR) project. It is preferred because it involves actual fluid displacement in a porous medium. However, the specific criterion for determining the cut-off point during the measurement is not uniquely agreed upon in the literature. Different criteria have been proposed by researchers and this has been one of the setbacks of using Slimtube measurements. The most commonly used criterion is the 1.2 PV criterion, which uses the recovery after injecting 1.2 pore volumes of the displacing gas as the cut-off. However, experimental observations show that even at supercritical condition, the volume of a gas is a strong function of the experimental pressure. Therefore, there is a need to develop an alternative means of determining the MMP that is not subject to particular pore volumes injected during Slimtube measurements. This work presents different means of determining the MMP, based entirely on recovery and the particular displacement phe-nomenon. In this approach, two new parameters are defined - the instantaneous recovery rate (IRR) and the oil recovery rate (ORR). The maximum values for these parameters for each experiment are used as the cut-off value. This new criteria was used in analyzing nine experimental data using oil from the Permian Basin. The results were compared with MMP prediction based on maximum recovery from each of the runs and the results were found to be in agreement. These new criteria will provide consistent cut-off point for experimental runs because Slimtube measurements take a long time to complete. The new procedure ensures that adequate data have been gathered during each experimental run, sufficient for a consistent experimental analysis.