Madden deep unit of the Wind River Basin: A new frontier formation play

The Madden Deep unit, located in the Wind River basin of central Wyoming, has been a source of natural gas production from Upper Cretaceous and Lower Tertiary formations. Drilling in excess of 24,000 ft occurred during the mid-1980s and early 1990s to explore for and develop Paleozoic gas potential. These well bores penetrated the Upper Cretaceous Frontier Formation at depths below 20,000 ft. Open-hole logs, cores, and drilling cuttings suggest a significant gas accumulation within the Frontier. The Frontier Formation represents a series of coarsening-upward, shallow-marine sequences deposited as a seaward-stepping system along the Western Cretaceous Seaway margin. In Madden field, the fifth bench of the Frontier contains traditional facies from foreshore/beach, to upper and lower shoreface, to offshore regimes. Common to deposites elsewhere, the best reservoirs are found in the foreshore/beach settings at the top of the bench. Production is not related to easily understood porosity regimes; primary intergranular porosity is virtually nonexistent. An overpressured reservoir with numerous vertical/subvertical fractures accounts for production. Microfractures and megafractures, up to 10 mm across, provide permeabilities that exceed 1 d. Fractures are partly filled by abundant quartz and minor calcite. Mineralization would allow singificant reservoir pressure drawdown without reducing aperture width. Majormore » fractures apparently strike west-northwest, and such orientation data may permit a horizontal drilling venture when technology is capable of surviving such deep, overpressured, and high-temperature environments.« less