ABSTRACT

Since 1952, Paleozoic carbonate rocks beneath the Fort Peck Reservation have produced 83 million barrels of oil. Of the 1000 exploration wells drilled in the last 40 years more than 300 have been successful. Reservoirs are primarily in the Mississippian Charles Formation (56 MMBO produced) and the Devonian Nisku (Birdbear) Formation (22 MMBO produced). The Charles production has been mostly at Poplar dome and Lustre field, however ten other fields have produced from Charles age rocks. Limited production is found in the top of the Mississippian Mission Canyon Formation in two fields.

Other formations producing oil on the Reservation include: Devonian Duperow (2 fields), Winnipegosis (1 field), Silurian Interlake (1 field), Gunton (1 field), and Ordovician Red River (4 fields). Significant Winnipeg gas DST recoveries have also been reported in, and adjacent to, the Reservation.

Charles reservoirs are usually less than 6,000 ft (1829 m) deep and are driven by solution gas and or water. Initial production rates are typically less than 200 BOPD, yet many Poplar wells were considerably better (500-6,000 BOPD). Charles wells produce less than 200,000 barrels, usually under 10-15% exponential declines. Unitization has kept many Poplar wells producing long past normal economic lives. Fracturing is now thought to be important in enhancing Charles reservoirs, especially in the newer fields. Salt dissolution events and timing are emphasized in an interpretation of the Poplar reservoir.

The Nisku tantalizes explorationists with small, high volume structures, thought to form over two-stage salt dissolution features. Nisku wells typically began at more than 500 BOPD and through long lives, at recurrent hyperbolic decline rates, can produce more than a million barrels. Depths average 7500 ft (2286 m).

Fields adjacent to the Reservation's eastern edge have produced more than 13 million barrels mainly from the Ordovician Red River Formation, at depths of 10,700 ft (3262 m). Reservation fields have proven reserves of at least 18 million barrels.