SUMMARY

The Weyburn Unit which covers 52,000 acres is located 10 miles south-east of the town of Weyburn, and 80 miles south e of Regina, the provincial capital of Saskatchewan, Canada. Production consists primarily of medium gravity (25-34°API) sour etude oil with a low GOR.

The field was discovered in 1954 by Central Del Rio Oils Limited, which became part of PanCanadian in 1971. The field was fully delineated by 1960 with vertical wells drilled on 80 acre spacing. The Weyburn Unit was formed in 1962 and a waterflood was implemented employing 151 inverted nine-spot patterns in 1964. A year later oil production peaked at 47,175 barrels per day. Production decline was arrested with the drilling of 157 vertical wells between 1985 and 1992.

Due to declining economics of the vertical infill wells, a horizontal pilot program was initiated in 1991. The success of the pilot led to a commercial scale drilling program which is currently in its 15th phase of drilling. With advancements in technology, the program has evolved from 1,100 foot, single overbalanced lateral wells to dual-build, underbalanced multi-lateral wells with in excess of 12,000 feet of reservoir exposure.

In 1996, oil production averaged 22,694 barrels per day and cumulative production reached 328 million barrels of oil or 25% of the 1.28 billion barrels of OOIP. There are currently a total of 981 wells; 534 vertical oilwells, 130 horizontal oilwells, 171 water injectors and 146 suspended or abandoned wells. The treated oil is shipped to markets in the U.S. Midwest and Central Canada.

The reservoir consists of the naturally fractured Midale Beds of Mississippian age. The Midale Beds are subdivided into an upper chalky dolostone, the Marly and a lower heterogeneous limestone, the Vuggy. Waterflood injection occurs primarily in the Vuggy zone which provides bottom water pressure support for the horizontal wells.

On June 26, 1997, PanCanadian as Unit operator and on behalf of the 37 Partners in the Unit, announced the Weyburn CO₂ miscible flood project. The project is forecast to boost oil production from the Unit to 30,000 barrels per day by the year 2008.

A carbon dioxide (CO₂) miscible flood differs from a waterflood in that water is generally used to sweep or push oil to the producing wells in an effort to improve recovery efficiency. A miscible flood is an enhanced oil recovery (EOR) technique. When the CO₂ is injected under pressure it dissolves in the oil. The CO₂ acts as a solvent to overcome the forces trapping the immobile oil that has been left in the pore system after waterflooding. The carbon dioxide causes the residual oil to swell and lowers its viscosity, making it mobile. Ideal conditions for a miscible flood include a depth of at least 2,500 feet to allow for the high pressures needed to ensure miscibility of oil and CO₂, and an oil gravity of at least 25 ¯API. The Weyburn Unit is an ideal candidate for application of miscible flood technology due to its unique fluid and reservoir characteristics. Similar miscible floods are currently operating at the neighboring Midale field in Saskatchewan, and at the Harmattan East and Joffre fields of Alberta.

The CO₂ used in the miscible flood will come from the Great Plains Synfuel Plant in Beulah, North Dakota. The plant owner, Dakota Gasification Company (DGC) of Bismarck, N.D. will build a 200 mile CO₂ pipeline for deliveries in the 2nd to 3rd quarter of 1999.

Construction of facilities for the Weyburn CO₂ miscible flood project will take 24 months with initial CO₂ injection in 19 patterns. By the year 2001 this will be expanded to 36 patterns; and 75 patterns by 2010 with an expected incremental recovery of 122 million barrels. There is the potential to miscibly flood the entire Unit.