The recent period of depressed oil prices which reached as low as $US 5.97/bbl for heavy oil drove major reviews in heavy oil recovery economics, and led to a substantial shift in the operation of four (4) of Petrotrin's thermal projects. The shift was predicated upon key factors such as:

  1. experience derived from the North Fyzabad project, a mature steamflood which was converted to a heat scavenging project in 1996

  2. the need to assure project viability by maintaining a reasonable lifting cost.

  3. at least sustain the present level of decline rates associated with each project.

In February 1999, North Palo Seco, Apex Quarry and Bennett Village, three (3) mature thermal projects at Petrotrin were placed on the water-alternating-steam-process (WASP) and another, Central Los Bajos was converted in August 1999. The four (4) projects are in close proximity each exploiting the Lower Morne L'enfer sandstone and their operating and reservoir characteristics are quite similar. In two (2) of the schemes, selected patterns were converted to WASP, the other patterns being kept on continuous steam. The criteria for pattern selection were pattern temperature, steam-oil-ratio, produced WOR, susceptibility to steam breakouts, and minimal alteration to main piping system.

The paper discusses capital expenditure for the conversion which was kept to an absolute minimum, operating cost which was subsequently reduced; profitability which increased; reservoir response to water injection which resulted in an increase in oil production rate and problems associated with implementation. The paper also discusses techniques of day-to-day flood monitoring, highlights operational problems and presents future operating strategies.

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