--> Fractured Oil Reservoirs of the Mancos Formation, Eastern San Juan Basin, New Mexico: Best in the Rockies, by P. A. Dea, B. C. Boyce, T. A. Casey, and T. Velarde; #90986 (1994).

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Abstract: Fractured Oil Reservoirs of the Mancos Formation, Eastern San Juan Basin, New Mexico: Best in the Rockies

Peter A. Dea, Bradford C. Boyce, Tom Ann Casey, Thurman Velarde

The San Juan basin of northwestern New Mexico has produced the most oil from any fractured shale reservoir in the Rocky Mountain region. The Mancos Formation of the San Juan basin has yielded nearly 30 million barrels of oil (MMBO). Approximately 75% of the total, 23.3 MMBO, has come from four fields on the eastern rim of the basin. A recent horizontal well on the Jicarilla Apache Reservation discovered a new 5-10 MMBO Mancos field, extending this prolific trend north of the existing fields. The Jicarilla 3-F has been flowing at rates of 300-800 barrels of oil since 1992.

The oil-bearing reservoirs of the Mancos occur in brittle dolomitic siltstone beds interbedded with more plastic shale of the Niobrara member. The horseshoe-shaped monoclinal flexure surrounding the basin controls the fractured reservoirs. Five structural settings of fracture intensity and oil production are associated with the monocline. These include monoclinal flexure, basal monoclinal flexure, anticlinal nose, synclinal trough and central basin structures. The common structural traits are maximum curvature of the brittle beds and a sudden change in the rate of dip.

Cumulative oil recoveries vary widely, ranging up to 2,465,000 barrels per well. Most of the variability appears related to the type of drive mechanism. Gravity drainage, utilizing gas injection wells and 640 to 1280 acre spacing, recovers 5 to 10 times more oil than solution gas drive.

The prolific fractured Mancos oil trend continues north of the recent discovery on nearly 100,000 acres of untested area within the Jicarilla Indian Apache Reservation. The Jicarilla Apache Tribe, through their Oil and Gas Administration, offers an attractive business and geologic environment for oil and gas exploration and development.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994