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Abstract: Reservoir Characterization of a Heterolithic Carbonate Mound, Runway Field, Paradox Basin, Utah

LORENZ, DOUGLAS M., REGA, Inc.; W.E. CULHAM, REGA, Inc.; T.C. CHIDSEY, JR., Utah Geological Survey; KRIS HARTMANN, Harken Southwest Corp.

The Pennsylvanian (Desmoinesian) Desert Creek carbonates of Runway field in the Paradox basin of southeastern Utah provide an unusual opportunity for evaluating the utility of detailed geostatistical characterization of an areally restricted, heterolithic carbonate mound reservoir. This investigation is part of Phase I in a DOE Class II Shallow Shelf Carbonate Reservoir demonstration of cost-effective methods for improving oil recovery from this and similar small (2 to 10 million barrels [0.32-1.59 million m{3}]) carbonate mound fields.

The Desert Creek carbonate mound at Runway field is a lenticular, lobate buildup 0.9 miles (1.5 km) long and 0.5 miles (0.8 km) wide, encompassing almost 200 acres (80 ha), with net pay thickness of 60 to 80 feet (18-24 m). It is comprised of a variety of carbonate lithotypes, which are particularly heterogeneous in the upper 60 percent of the reservoir. In common with more than a dozen other similar mound buildup reservoirs on the periphery of the giant Greater Aneth field, stratigraphy in the Runway mound consists of three distinctly different carbonate sequences: an underlying series of tight, non-reservoir mudstones and finely crystalline dolomites (platform interval), overlain by a sequence of phylloid-algal limestones and bryozoan-dominated lime-mudstones (mound-core interval), capped by a series of interbedded lime mudstones, packstones/wackestones, skeletal grainstones, and dolomites (supra-mound interval).

Three wells, two regularly spaced seismic swath surveys, pressure buildup tests on all three wells, and seven years of production history provide the data for characterizing the Runway reservoir. Based on previous work on the nearby Anasazi reservoir and detailed core descriptions from two Runway wells, nine lithotypes were identified for characterizing internal reservoir architecture. A two-stage conditional geostatistical modeling procedure was employed: first the lithotype bodies were emplaced using a marked point (Boolean) stochastic process, then reservoir properties were distributed within this architecture using simulated annealing, based on indicator variograms and average porosity distributions obtained from seismic amplitude data.

Despite significant differences in carbonate lithotype composition and detailed stratigraphic development in the Runway and Anasazi reservoirs, the successful implementation of similar reservoir modeling procedures demonstrates the flexibility and general application of such hybrid techniques. These methods can serve as prototypes in characterizing other carbonate mound reservoirs for simulation, production forecasting, and enhanced recovery development planning.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah