Oil production along the east-west trending Duchesne Fault Zone of northeastern Utah has continuously mystified oil and gas operators, past and present. Unusual production, both positive and negative, has resulted from conventional fracture stimulation of traditional sandstones mainly encompassing the Green River and Wasatch formations (Eocene).

Also, shallow (2000 ft ±) production from Green River oil shales has long been recognized particularly from the Duchesne and Bridgeland fields near the western end of the forty mile lineament. In order to maximize both primary and secondary recovery from both kinds of reservoirs, detailed surface mapping and fracture analysis have concluded that east-west faults and paralleling fractures were later affected by northwest trending patterns, all of which contain gilsonite hydrocarbon bodies. Surface sandstones, unlike interbedded carbonates and shales, contain an orthogonal fracture set, the orientation of which is modified by internally variable cross-bedding patterns.

An oriented core and formation imaging log from a test well operated by Equitable Resources, Inc., have revealed the presence of visibly fractured feldspathic litharenites responsible for much of the erratic production. Additionally, dip-slip movement has produced local steepening of beds which could provide structural closure against the near-vertical fault planes.

Future subsurface work in 1997 will focus on the shallow, over-pressured oil shale production, which undoubtedly exists for some distance away from the established Duchesne and Bridgeland fields. The possibility of horizontal drilling in both plays should be strongly considered by all operators.