Four (4) immiscible Carbon Dioxide (CO2) pilot floods were implemented between 1973 to 1990 in the Petroleum Company of Trinidad and Tobago’s (Petrotrin’s) reservoirs at its Forest Reserve and Oropouche fields, Trinidad. CO2 was sourced from an ammonia plant and piped twenty-five (25) miles to the fields. The projects were conducted in a gravitystable mode after primary, secondary and tertiary production (after natural gas and water injection). CO2 was injected into thick sands of variable continuity containing medium gravitycrude (17 to 29o API). Production increases were observed in all projects. Injected CO2 probably swelled the oil, reduced viscosity and helped form oil banks that could move easier under gravity. Oil production rates and recovery improved as a consequence. In some of the projects, these beneficial effects continued for many years even after discontinuation of CO2 injection (supply interruptions) aided by water influx. Interruptions in CO2 supply did not seem to harm incremental oil recovery materially. Channeling was observed at high injection rates and promoted in reservoirs with low transmissibility.Oil recovery improved as more offtake (production) wells were added downstream of the injection wells. This reinforced the importance of optimizing volumetric sweep, and of capture during CO2 flooding by judiciously selecting injection and off- take locations. Incremental recovery ranges between 2 to 8% of the Original Oil in Place (OOIP) with predicted ultimate recoveries of 4–9% of the OOIP. Cumulative CO2 utilizations improved with efficient production practices and range from 3-11 Mcf/bbl to date.Exploitation of similar reservoirs was indicated for increasing production/ recovery via CO2 injection. Learnings from the four (4) CO2 projects analysed can be used to define selection criteria for new CO2 injection projects and to improve management of existing projects.
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