Redevelopment of the Brazeau River Nisku A And D Vertical Miscible Floods With Horizontal Wells

Abstract

Abstract 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 m3/d, and the expected incremental reserves are approximately 300,000 m3 for the Nisku A pool and 260,000 m3 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. Introduction The Brazeau River Nisku A and D pools are located approximately 150 km southwest of Edmonton, Alberta. Figure 1 shows the location of the Brazeau River Nisku A and D pools along with other producing Nisku reefs in the area. The first A pool well, 11- 31–48-12 W5M, was drilled in January 1978. The Nisku D pool was discovered in June 1978 with the drilling of well 7–33-48–12 W5M. The A and D pools are both sweet oil reservoirs containing light, volatile oil having a density of approximately 800 kg/m3. The respective solution GORs were 180 and 140 m3/m3. Average porosity ranges from 7 to 10% and the respective net pays are 80 m and 40 m. Average pool permeability of the A pool is 330 mD while the D pool is significantly lower at 50 mD. Table 1 summarizes the reservoir properties of the Nisku A and D pools. The oil properties and pressure information are described in Table 2. The Nisku reefs are of the Upper Devonian Winterburn group at a depth of 3,200 m. The base of these reefs covers approximately one section (259 ha) in areal extent. The Nisku A pool is almost entirely dolomitized containing moldic vuggy pores. In the Nisku D pool, sparry calcite cement results in porosity and permeability reduction by complete or partial plugging of both intercrystalline and moldic vuggy pores. The reefs are extremely variable in terms of primary facies and diagenetic modifications; therefore, reservoir properties are difficult to correlate between wells.