A Quarter Century of Progress in the Application of CO2 Immiscible EOR Project in Bati Raman Heavy Oil Field in Turkey

Abstract

The Bati Raman field is the largest oil field in Turkey containing approximately 1.85 billion barrels of initial oil in place at an average depth of 4300 ft. The oil is heavy (12 o API) with high viscosity and low solution gas. Primary recovery between 1961 and 1986 was less than 2% of OOIP.The commercial CO 2 -EOR project began in 1986 and is still active. With the implementation of the CO 2 flood, the recovery is expected to potentially reach up to 10% of OOIP.The reservoir rock is naturally fractured carbonate where the heterogeneities and the unfavorable mobility ratio of CO 2 and crude caused inefficient sweep. The solubility of CO 2 in the oil, which is highly sensitive to reservoir operating pressure, was a significant factor for the success of the CO 2 flood. Currently, the injected agent is increasingly bypassing the remaining oil and the production is curtailed by excessive high gas/oil ratio (GOR) severely jeopardizing recovery. These conditions prompted the use of applications of the conformance-improvement systems in the wells in western part of the field.Successful applications of fracture plugging polymer gel system intended for the conformance improvement were carried out in the years of 2002 and 2004. Also, to improve the recovery by a better sweep (or displacement), a chemically augmented water injection process was proposed in the areas having relatively lower reservoir pressure. Chemicals were tested for wettability alteration and IFT reduction to select the best performing ones. After an economic analysis, a field trial of the water alternating gas (WAG) injection process with caustic was put into progress in 2010.Optimized application cases were determined by tuning the total gas injection rates of the field, proration of the individual well rates according to the GOR, investigation of infill drilling, and alteration of the gas injection pattern, based on the results of the simulations carried out in different time frames of the project history.The Bati Raman immiscible CO 2 injection project has been acknowledged as one of the most unique and successful enhanced oil recovery (EOR) applications in the history of fractured heavy-oil carbonate reservoirs. This paper presents a comprehensive overview of this project after a quarter century of experience. IntroductionBased on its in-situ gravity of 12º API and viscosity of 600 cp, the Bati Raman oil is classified as extra heavy. Due to adverse oil properties (12º API viscosity of 600 cp, and low solution gas), low reservoir energy and heterogeneity caused by naturally fractured and vuggy structure, only 1.7 percent of the OOIP corresponding to 32 million STB, was produced prior to CO 2 application. All primary recovery was due to fluid and rock expansion. With a drastic drop of pressure in reservoir after a short period of time the effect of solution gas drive was dwindled. Hence supplemental recovery through EOR was called for. Water drive resulted in insignificant additional oil; consequently, the field was extensively studied for an efficient...

CO2 retention values in enhanced oil recovery

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