TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractTerra Nova oil pool is the second largest

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% C 2+ 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.

A 400 m long horizontal well was drilled in both the Brazeau River Nisku A and D pools at a true vertical depth of 3,200 m. Both pools have been under vertical hydrocarbon miscible floods for over ten years. The purpose of these horizontal wells was to increase ultimate pool recovery by reducing well drawdown leading to improved GOR behaviour.The location of the horizontal well in the Nisku A pool was selected based on the existing 2-D seismic data in an effort to further exploit the undeveloped portion of the reservoir. Two side track horizontal holes were drilled to search for the porous zone in the bottom of the reservoir prior to drilling the final horizontal hole approximately 2m above the base of the porous zone. In the Nisku D pool, vertical seismic profiling was conducted to locate the porous zone and to aid in the design of the length, depth and azimuth of the horizontal wellbore.Both wells were open-hole completed. The initial oil rates were 300 -400 m 3 /d, and the expected incremental reserves are approximately 300,000 m 3 for the Nisku A pool and 260,000 m 3 for the Nisku D pool, or 4 and 10% of their respective OOIP. Because of the relatively high initial oil rate of the horizontal wells, the high expenditures of $5 million for the Nisku A pool and $3.4 million for the Nisku D pool were paid out during the first year of production. K J F M E L G C A 62 The Journal of Canadian Petroleum TechnologyFIGURE 5: Nisku A pool GOR history. FIGURE 7: Nisku D pool oil rate. FIGURE 6: Nisku D pool reservoir pressure history.