WEBER, L. JAMES, J. F. SARG, and F. M. WRIGHT, Mobil Exploration and Producing Technical Center, Dallas, TX

ABSTRACT: Reservoir Delineation and Pore System Characterization through Use of Sequence Stratigraphy: An Example from the McElmo Creek Unit, Greater Aneth Field, SE Utah

Nineteen discrete and mappable high-frequency depositional cycles are recognized within three depositional sequences of the Desert Creek and lower Ismay section (middle Desmoinesian) at the McElmo Creek Unit of the Greater Aneth field, southeastern Utah. Significantly, facies stacking within parasequences permits us to (1) map and predict the distribution of porous and permeable facies and (2) characterize variability in reservoir pore systems. This work will assist greatly in future reservoir management.

At McElmo Creek stratified reservoirs occur within transgressive, highstand, and lowstand systems tracts. Within transgressive systems tracts, dolomudstone/wackestone of the lagoon/tidal flat environment comprise parasequences and display intercrystalline and solution-enhanced secondary porosity. In the lower Desert Creek, initial parasequences of the highstand systems tract represent a time of mound building and platform development as a result of coalescing biologic communities of phylloid algae; interparticle and shelter porosity dominate. Subsequent parasequences within the lower Desert Creek highstand systems tract exhibit skeletal and nonskeletal wackestone to grainstone. Porosity is developed on paleodepositional highs at the top of parasequences where shoal water facies reveal preserved primary pore systems that are secondarily enhanced by leaching of less stable carbonate minerals by meteoric water. In the upper Desert Creek highstand systems tract, oolitic grainstone occurs beneath the 3rd-order sequence boundary and displays oomoldic porosity. In a basin margin position, adjacent to the Aneth platform, hydrocarbons are produced from downslope allochthonous peloidal and oolitic grainstone debris aprons. Siltstone, dolostone, and evaporites form lowstand wedges that were deposited 150 feet below the crest of the Aneth carbonate platform. Porous dolomudstone and dolowackestone are productive where they onlap and pinch out against the Aneth carbonate platform.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.