The Weybum Unit is one of the largest medium-sour crude oil reservoirs in Canada, containing approximately 207 E6 m3 of original oil in place. The field was discovered in 1955 and has been on water flood since 1964. The Weyburn Unit includes 530 production wells and 170 water injectionwells. This includes the vertical infill wells added in the mid 1980's and over 140 horizontal wells which were added over the past seven years.

The Weybum Unit has been a successful operation for PanCanadian Resources and for the many working interest owners in the Unit. However, the field is a mature water flood with high water cuts and decreasing oil production.Without some kind of tertiary recovery, it would soon become necessary to suspend or abandon large blocks of production wells in the Unit. The development of a large scale CO, flood in the Weybum Unit will be the most significant development in the SE Saskatchewan oil patchsince the discovery of the Weybum field.

The Weybum Unit covers 180 km2 in southeastern Saskatchewan. The Weybum oil pool produces 25 to 34 degree API medium gravity sour crude from the Midale beds of the Mississippian Charles formation. The are twolayers in the Midale beds, the Marly zone and the Vuggy zone. The Marly is a chalky dolomite with low permeability. Below the Marly is the Vuggy zone, a highly fractured and permeable limestone. The water flood whichwas developed in the 1960's has recovered most of the oil from the Vuggy zone but much less of the oil from the MarIy zone.

The production responsibilities of the Weybum field operators have been well defined for the water flood operation. Water injection rates are optimized in many parts of the field to maximize oil production. Water distribution is adjusted to maintain the target voidage replacement ratios. Pump-off controllers have been installed on many wells to improve rod pump reliability and to minimize the production well down hole pressure.

The construction of a commercial scale CO2 flood will cause a step change in the complexity of the Weyburn production operation. The operator will be managing a valuable commodity, that is the CO2 itself, in order to maximize the production of oil. At the same time, the safe operation of the pipeline and satellites will be of utmost importance as high pressure sour gas is transported throughout the field. The field operator will become an important part of the commercial and social success of this project.

The stakes are high. By improving the recovery of oil in this Unit from the 30% anticipated with conventional water flood, an incremental 21 000 000 m3 of oil will be produced over the next 20+ years. This compares to the 53 000 000 m3 of oil which have been produced in the 40 years since the field was discovered.1

Two priorities in the execution of this project are training and safety. Training will be required to give the operating team the best understanding of the principles of CO2 miscible flooding.

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