Lessons From Trinidad's CO2 Immiscible Pilot Projects

Abstract

Summary Four immiscible carbon dioxide (CO2) pilot floods were implemented in the Petroleum Co. of Trinidad and Tobago's (Petrotrin's) reservoirs at its Forest Reserve and Oropouche fields, Trinidad, over the period 1973 to 1990. The projects were conducted in a gravity-stable mode after primary, secondary, and tertiary production (after natural-gas and water injection). CO2 was injected into thick sands of variable continuity containing medium-gravity crude (17 to29°API). Production increases were observed in all projects. It is postulated that injected CO2 swelled the oil, reduced viscosity and helped form oil banks that could move more easily under gravity. Oil-production rates and recovery improved as a consequence. In some of the projects, these beneficial effects continued for several years, even after discontinuation of CO2 injection(supply interruptions), with recovery aided by water influx. Interruptions in CO2 supply did not appear to harm incremental oil recovery materially. Channeling was observed at high injection rates and was promoted in reservoirs with low transmissibility. Oil recovery improved as more offtake (production) wells were added downstream of the injection wells. This phenomenon reinforced the importance of optimizing volumetric sweep and of capture during CO2 flooding by judiciously selecting injection and offtake locations. Incremental recovery ranges between2 and 8% of the original oil in place (OOIP), with predicted ultimate recoveries of 4 to 9% of OOIP. Cumulative CO2 use improved with efficient production practices and ranges from 3 to 11 Mcf/bbl to date. Introduction The Forest Reserve and Oropouche fields are located in the southwest peninsula of the island of Trinidad, as shown in Fig. 1. In 1973, CO2 injection was initiated into a former natural-gas-injection project in Forest Reserve when there was a shortage of natural gas. Three immiscible pilot floods and one cyclic-injection project were later implemented between 1974 and 1986. Another immiscible pilot flood was implemented in 1990 in the Oropouche field. These projects were implemented in a "poor boy" mode using existing wells and equipment. CO2 is piped 25 miles from an ammonia plant, compressed, and injected into target reservoirs. This paper documents Petrotrin's 30 years of experience1 with CO2 immiscible injection into these projects and presents a comparative analysis of the performance of the four enhanced-oil-recovery (EOR) projects with some immiscible CO2-flood projects from the literature. Results and lessons learned will be used to guide the extension of CO2 injection to other similar reservoirs in the company's operations and to improve the management of existing projects.

An Experimental and Modeling Study on Interactions of Cold Lake Bitumen with CO2, C3, and C4 at High Temperatures

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The Impact of the Clean Development Mechanism and Enhanced Oil Recovery on the Economics of Carbon Capture and Geological Storage for Trinidad and Tobago

“…Secondly, this "source area" is relatively close to potential geologic storage sites. These potential sites include the spent oil fields in the Fyzabad and Oropouche areas [6] and the gas fields and saline aquifers off the east coast of Trinidad [3]. Thirdly, transportation and compression costs would be relatively lower in T&T because of the comparatively cheap cost of electricity and the close proximity of the storage sites.…”

“…Past CO 2 flooding projects in Trinidad illustrated a CO2 consumption rate of about 8 Mcf/bbl [6]. Given the density of CO 2 , this translates into 0.45 tonnes CO 2 to recover 1 barrel of oil.…”

“…Historical data for similar projects suggest that an initial productivity rate of about 300bbls/day is normal [6]. The EOR technology has since advanced and for this paper we assume an average initial productivity rate of 450 bbls per day.…”

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