Determination of the Minimum Miscible Pressure of the Supercritical Carbon Dioxide and the Formation Oil System by the Pendant dro‎p Method

Carbon dioxide miscible displacement plays an important role in the field of miscible displacement for enhanced oil recovery. However, there is a very important relationship between the formation of miscible displacement and the minimum miscible pressure. The pendant drop method in the interfacial tension method was firstly used to predict the minimum miscible pressure of the supercritical carbon dioxide and the formation of oil in the test area oilfield. Under the condition of the simulated reservoir temperature 111.5 °C, the interfacial tension of the supercritical carbon dioxide and the formation oil system was tested experimentally by using formation oil samples of the test area oilfield. The range of test pressure was from 10.06 MPa to 28.57 MPa. Besides, the relation curve of the test pressure and the interfacial tension was drawn. The results show that under the reservoir temperature, the interfacial tension between the supercritical carbon dioxide and the formation oil shows an approximately linear downward trend with increasing the test pressure. The mathematical expression was obtained by the linear regression analysis. According to the extrapolation, the vanishing point of the interfacial tension was obtained. Then the minimum miscible pressure of the supercritical carbon dioxide and the formation oil system was determined. The actual test was carried out to verify the result by the pendant drop method. Finally, the minimum miscible pressure of the supercritical carbon dioxide and the formation oil system of the test area oilfield was determined to be 29.4 MPa.