In early 2001, Terra Nova is expected to start production at an average rate of 115,000 barrels of oil per day. Terra Nova oil pool is the second largest oil pool discovered in the Grand Banks of the Canadian East Coast. As a part of the oil recovery process optimization effort, miscibility conditions were evaluated using different techniques, for Terra Nova oil with various gas streams available from the offshore production facilities.
The techniques used consisted of the conventional slim-tube test, the rising bubble apparatus and the recently developed Vanishing Interfacial Tension (VIT) technique. In addition, published correlations were also used in estimating minimum miscibility pressures. This paper presents the results of these experimental studies and compares them with predictions from correlations as well as with visual evidence of miscibility.
The VIT technique is based on the fundamental definition of miscibility as the point at which the interface between gas and oil vanishes or the interfacial tension diminishes to zero. A computerized drop shape analysis technique was used to determine gas-oil interfacial tensions.
The miscibility pressures obtained from the new VIT technique were 3–5% higher than those from visual observations and agreed well with the slim-tube results as well as with the correlations, at enrichment levels greater than 30 mole% C2+ in the injected gas stream. The rising bubble apparatus yielded significantly higher MMPs. This study demonstrates that the VIT technique is rapid, reproducible and quantitative in addition to providing visual evidence of gas-oil miscibility.
The recent world-wide survey of enhanced oil recovery (EOR) projects conducted by the Oil and Gas Journal1 indicates that even with the uncertainty caused by the oil price collapse prior to mid-1999, operators still see EOR processes as opportunities for increasing recovery factors from known oil accumulations. This survey lists 18 field-wide or pilot gas injection projects planned to start between 2000 and 2001 which includes 7 CO2 miscible projects, 7 hydrocarbon miscible projects, 2 hydrocarbon immiscible WAG projects, and 2 nitrogen projects in the world. The size of these projects range from 10 acres for the Sprayberry Trend in Midland County in Texas to 52,000 acres for the PanCanadian's CO2 flood in the Weyburn Unit in Saskatchewan. The survey concludes that EOR processes have weathered the low oil price environment of the last two years and continue to contribute significant oil production.
Terra Nova, discovered in 1984, is the second largest oil pool in the Grand Banks of the Canadian east coast. It is located 350 kilometers south-southeast of St. Johns, Newfoundland in 95 meters of water depth. It is anticipated to start production in early 2001 at about 115,000 barrels per day. The production strategies considered for Terra Nova included waterflood, solution gas injection for gas storage and enriched gas injection for miscible flood.
In order to evaluate the potential for carrying out a miscible flood in Terra Nova, miscibility conditions were determined for Terra Nova live oil and several field gas streams of differing compositions using the slim-tube displacement test, rising bubble apparatus and the recently developed Vanishing Interfacial Tension (VIT) technique.