Abstract
Current exploration activity in the northern portions of the Pleasant Valley-Monument Butte fields has been given great impetus by enhanced fracture permeability in what are generally low-permeability sandstone reservoirs. Associated with the Duchesne fault zone, these fractures trend both parallel to existing faults (approximately east-west), and oblique to structural trends (approximately northwest). Extensive coring has substantiated the existence of fractured reservoirs in both the green shale and black shale facies of the Green River Formation (Eocene), although some fracturing is probably compaction induced. Gilsonite orientation can serve as a finger post to these fracture systems in that many gilsonite veins parallel fracture traces. Other gilsonites parallel apparent rollovers or open anticlinal features as expressed on the surface. These extremely gentle folds generally trend northeast and may also be a clue to increased production. Finally, updip truncation of reservoir sandstones by high-angle faults represents another concept related to increased Green River recoveries. Some faulted sequences dip rather severely to the north (15°-30°) compared to the regional dip (2°-3°). These displaced strata may contain a known reservoir whose hydrocarbon contents are trapped against one of these east-west lineaments of the Duchesne fault zone. End_of_Article - Last_Page 932------------
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