Monitoring The Performance Of Pembina Nisku Miscible Floods

Abstract

Abstract Esso Resources Canada Ltd. operates gravity-stable hydrocarbon miscible floods in seven Pembina Nisku pinnacle reefs. All these floods were started between 1982 and 1985 and recovery from the more mature floods has exceeded 50% of original-oil-in-place (OOIP), During 1989 a number of infill wells were drilled to maintain productivity and reduce solvent coning. Open hole gradiomanometer logs were run in these wells to determine gas, solvent, oil and water contacts. Previous cased hole contact logging had been unsuccessful and these infill wells afforded an opportunity to assess the progress of the miscible floods with open hole contact logs. This paper reviews the performance of the miscible floods and describes the results of the contact logging, The implications of the contact log results are discussed in regard to solvent bank dispersion, volumetric conformance and displacement efficiency, and future infill drilling and completion strategy. Introduction Sequence of Development The Pembina Nisku pinnacle reefs are located approximately 160 km southwest of Edmonton. Figure 1 shows the 17 Esso working interest pools in the area of which eight are waterfloods and nine are vertical miscible floods. Esso operates seven of the miscible floods. The Pembina Nisku G and K pools were the first pools to be miscibly flooded. After primary depletion to the bubble point pressure (between 1978 and 1979) the pools were shut in until 1981, when facilities were in place to commence miscible flooding. As shown in Table 1, the cumulative recovery to date (1989 year-end) is 56% and 50% of OOIP for the G and K pools, respectively. The Pembina Nisku O and P pools followed with miscible flood start up in 1983. These pools have produced 40% and 44% of their respective OOIPs to date. M pool was a Getty Oil pool, later acquired by Texaco, which also started miscible flooding in 1983. It has a recovery to date of 48% of OOIP. Pressure maintenance in the largest of the Nisku pools, the L pool, began in 1981 with a waterflood. At that time there was a concern that a Cynthia shale tongue between the Upper and Lower Zeta Lake reef portions might be widespread laterally and disturb the solvent bank integrity in a miscible flood.. Subsequent infill drilling showed that the shale was localized in the region of the two southernmost wells. Consequently, waterflooding was suspended in 1985 and a miscible flood was started. Production of injected water also commenced that year as pan 0 f a scheme to recover residual oil in the water flushed zone. The Q pool also began miscible flooding in 1985. The cumulative production for the L and Q pools is 48% and 36% of their respective OOIPs. Prior to 1989 production was primarily constrained by market demands, the provincial allowable or Energy Resources Conservation Board (ERCB) maximum rate limitation (MRL) rates. In 1988 and 1989, solvent coning in wells completed at the base of porosity made it necessary to drill additional infill wells to reduce drawdowns and maintain pool productivity.