Methodology for Miscible Gas Injection EOR Screening

Abstract Miscible gas injection is the most widely applied light oil enhanced oil recovery (EOR) process. A methodology, based on well-established physical principles, has been developed for estimating the conditions under which gas will be miscible with oil. The methodology enables rapid screening of a range of potential gas injectants (such as CO2, enriched hydrocarbon gas, N2, or H2S) through the use of readily available gas and oil properties. The methodology has been applied to numerous reservoirs worldwide. An overview of the methodology is provided along with an illustration of its application to screening of gas injection EOR for the Malay Basin. The methodology makes use of a correlation1 that can be used to rapidly estimate miscible or near-miscible residual oil saturation, Sorm, minimum miscibility pressure (MMP), or minimum miscibility enrichment (MME) for a wide range of injected gases, crude oils, temperature and pressure conditions. The correlation is based on representation of the physical and chemical properties of the crude oil and injected gas through Hildebrand solubility parameters. Thirty-four offshore reservoirs operated by either ExxonMobil Exploration and Production Malaysia Inc. (EMEPMI) or production sharing contract (PSC) partners were screened for gas injection EOR. Potential injection gases included pure CO2, CO2 diluted with methane, field separator gas, CO2 enriched with LPG, and separator gas enriched with LPG. A spreadsheet was created to facilitate calculation of MMP or MME using the solubility parameter correlation for a large number of reservoirs and potential injection gases. The correlation was useful for ranking reservoirs and potential injectants with respect to gas injection EOR potential and identifying which reservoirs to carry forward for in-depth laboratory and simulation evaluation. In general, the predictions of the correlation compare reasonably with the more costly experimental data obtained in subsequent detailed evaluation.