Lessons from Trinidad's CO2 Immiscible Pilot Projects
- Lorna J. Mohammed-Singh (Petrotrin) | Ashok K. Singhal (Alberta Research Council)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- October 2005
- Document Type
- Journal Paper
- 397 - 403
- 2005. Society of Petroleum Engineers
- 6.5.2 Water use, produced water discharge and disposal, 5.4.2 Gas Injection Methods, 5.4 Enhanced Recovery, 4.6 Natural Gas
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Four immiscible carbon dioxide (CO2) pilot floods were implemented in thePetroleum Co. of Trinidad and Tobago's (Petrotrin's) reservoirs at its ForestReserve and Oropouche fields, Trinidad, over the period 1973 to 1990. Theprojects were conducted in a gravity-stable mode after primary, secondary, andtertiary production (after natural-gas and water injection). CO2 was injectedinto thick sands of variable continuity containing medium-gravity crude (17 to29°API).
Production increases were observed in all projects. It is postulated thatinjected CO2 swelled the oil, reduced viscosity and helped form oil banks thatcould move more easily under gravity. Oil-production rates and recoveryimproved as a consequence. In some of the projects, these beneficial effectscontinued for several years, even after discontinuation of CO2 injection(supply interruptions), with recovery aided by water influx. Interruptions inCO2 supply did not appear to harm incremental oil recovery materially.Channeling was observed at high injection rates and was promoted in reservoirswith low transmissibility.
Oil recovery improved as more offtake (production) wells were addeddownstream of the injection wells. This phenomenon reinforced the importance ofoptimizing volumetric sweep and of capture during CO2 flooding by judiciouslyselecting injection and offtake locations. Incremental recovery ranges between2 and 8% of the original oil in place (OOIP), with predicted ultimaterecoveries of 4 to 9% of OOIP. Cumulative CO2 use improved with efficientproduction practices and ranges from 3 to 11 Mcf/bbl to date.
The Forest Reserve and Oropouche fields are located in the southwestpeninsula of the island of Trinidad, as shown in Fig. 1. In 1973, CO2 injectionwas initiated into a former natural-gas-injection project in Forest Reservewhen there was a shortage of natural gas. Three immiscible pilot floods and onecyclic-injection project were later implemented between 1974 and 1986. Anotherimmiscible pilot flood was implemented in 1990 in the Oropouche field.
These projects were implemented in a "poor boy" mode using existing wellsand equipment. CO2 is piped 25 miles from an ammonia plant, compressed, andinjected into target reservoirs.
This paper documents Petrotrin's 30 years of experience1 with CO2 immiscibleinjection into these projects and presents a comparative analysis of theperformance of the four enhanced-oil-recovery (EOR) projects with someimmiscible CO2-flood projects from the literature. Results and lessons learnedwill be used to guide the extension of CO2 injection to other similarreservoirs in the company's operations and to improve the management ofexisting projects.
|File Size||1 MB||Number of Pages||7|
1. Bahaw, J.P.: "Enhanced Oil Recovery Using CO2—Trintoc's Experience toDate," paper presented at the 1991 10th Technical Conference and Exposition,Port of Spain, Trinidad, 26-28 June.
2. Mohammed-Singh, L.J. and Singhal, A.K.: "Lessons From Trinidad's CO2Immiscible Pilot Projects 1973-2003 ," paper SPE/DOE 89364 presented at the2004 SPE/DOE Symposium on Enhanced Oil Recovery, Tulsa, 17-21 April.
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