Abstract

Since discovery of the Aneth Field (1956), 360 MMBO (∼1250 MMOOIP) have been produced from Middle Pennsylvanian (Desmoinesian) carbonates of the Ismay and Desert Creek intervals. A sequence stratigraphic framework has been established for the Desmoinesian section in southeastern Utah using: 1) surface exposures at Honaker Trail, located 40 miles (64 km) west of the Aneth Field, 2) well logs near the outcrop area, and 3) core and well logs in the Greater Aneth Field. The sequence stratigraphic approach has allowed correlation of genetically related lithofacies. Bounding discontinuities (sequence boundaries and maximum flooding surfaces) have been correlated from the outcrop to the subsurface. Systems tracts of 3rd-order sequences are comprised of 4th-order sequences and 5th-order parasequences. The stratified reservoirs of Aneth occur within transgressive systems tracts (TST), highstand systems tracts (HST), and to a lesser extent lowstand systems tracts (LST).

Within the TST’s, dolomudstone/wackestone of the lagoon/tidal flat environment cap parasequences and display intercrystalline porosity. Phylloid algal mounds develop within the first shoaling cycle of the HST’s above the maximum flooding surface; interparticle and shelter porosity dominate. Subsequent parasequences within the HST’s exhibit porous and permeable skeletal and nonskeletal grainstone. Oolitic grainstone beds occur beneath the 3rd-order sequence boundaries and display interparticle and oomoldic porosity. In a basin margin position, adjacent to the Aneth platform, hydrocarbons are produced from downslope allochthonous HST oolitic grainstone beds. Siltstone, pervasively dolomitized cryptalgalaminite, and evaporites form lowstand wedges. Porous cryptalgalaminites may be productive where they onlap and pinch out against the Aneth platform.