The Rainbow Keg River "H2H" pool1 is a carbonate reef with only one well. The pool has an areal extent of 44 hectares. A thin oil zone of about five to seven metres thick is situated between a sizable gas cap and a strong water' drive system. The well was initially classified as a gas well when it was production tested in October, 1984. The average hydrocarbon liquid/gas ratio during the test was 160 m3/E6m3. It was later re-classified as an oil well effective 1989–03-01 due to the significant amount of oil produced along with the gas production. Because of its limited reserves, a single well gas flood was implemented to maximize the oil recovery and, at the same time, to minimize the capital investment. However, it is well known that this type of flood is risky, often with premature injected gas breakthrough at the producing interval causing extremely poor or even no sweep efficiency.
This paper focuses on Husky's engineering effort to effectively operate this flood by utilizing reservoir modelling technique, field operation techniques which included methanol injection, downhole choke installation t tracer survey, and cyclic gas injection pulsing/ production (CGIPP)2,3,4 technique. The flood has been in progress for over a year. The pool performance data shows a potential gain in incremental oil from the flood.
The Rainbow Keg River "H2H" pool is located in the Rainbow field, approximately 640 kilometres northwest of Edmonton, Alberta (Figure 1). It was discovered with the drilling of the 9-36-108–7W6 well in December, 1968. The 9–36 well was drill stem tested to produce commercial quantity of gas with a fair amount of hydrocarbon liquid. Due to the lack of gas market, the well was not completed for production until July, 1984.
In October 1984, a four-point modified isochronal test was run at the 9–36 well. The gas rate was tested at 189 E3m3 /d with a hydrocarbon liquid/gas ratio of 160 m 3 /E6m3. The hydrocarbon liquid analysis showed that it had an API gravity of 55.2 °. These test results concluded that the Rainbow Keg River "H2H" Pool was a rich gas reservoir.
The 9–36 well commenced production on 1985-08-22. It produced intermittently until October, 1988 when it was placed on steady production at a gas rate of 228 E3m3 /d with a hydrocarbon liquid/gas ratio of 175 m3 /E6m3. As production continued, the hydrocarbon liquid/gas ratio increased gradually. In March 1989, the hydrocarbon liquid/gas ratio dramatically increased to 413 m3 /E6m3 from 182 m3 /E6m3 measured a month before. The API gravity of the hydrocarbon liquid also decreased to 44.0 °. Consequently, the ERCB re-classified the well as an oil well.
This type of pool performance was unique among the Husky' s operated pools in the Rainbow field. A detailed engineering study was conducted to understand the reservoir and to develop an optimum hydrocarbon recovery scheme for the pool.
