--> ABSTRACT: Exploration Strategies for Deep Cretaceous Reservoirs in Rocky Mountain Basins, by Stephen A. Sonnenberg; #91030 (2010)

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Exploration Strategies for Deep Cretaceous Reservoirs in Rocky Mountain Basins

Stephen A. Sonnenberg

Exploration for Cretaceous reservoirs in the Rocky Mountain basins is currently aimed toward deeper areas. Cretaceous reservoirs in these deeper areas have been subjected to greater diagenesis and thus have significantly lower reservoir quality. Exploration strategies for these areas need to be modified. Exploration for deep reservoirs should include an analysis of basement tectonics, regional stratigraphy, geothermal gradients, and pressure gradients. The analysis of basement tectonics and regional stratigraphy may reveal favorable areas for paleostructural traps. Paleostructures may influence the original environment of deposition, fracturing, and diagenesis. The analysis of geothermal and fluid pressure gradients may reveal areas of significant hydrocarbon generation. aleostructural traps associated with high geothermal and fluid pressure gradients are viewed as the most favorable exploration areas. Examples of fields from the Denver and Powder River basins are illustrated to demonstrate these concepts.

The Wattenberg gas field is located in the Denver basin along the basin axis. Wattenberg is estimated to have reserves of 1.3 trillion ft3 in the J Sandstone over an area of 600,000 acres at depths of 7,600 to 8,400 ft (2,310 to 2,560 m). The field is regarded as a paleostructural trap associated with high geothermal gradients.

The Buck Draw field is located in the deep (> 12,000 ft; 3,657 m) overpressured portion of the Powder River basin and produces from the Fall River (Dakota) Sandstone. Individual wells are capable of producing over 2,000 bbl of oil/day from a naturally fractured reservoir. The fractures are created by abnormally high fluid pressures.

The results of this study may aid exploration for deep Cretaceous reservoirs in Rocky Mountain basins.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.