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Abstract

Reservoirs in deep-water sandstones of the Delaware Mountain Group in West Texas and New Mexico have low primary recovery efficiency (<14 percent). Reservoir characterization of a representative Delaware Mountain Group field was performed to identify geologic constraints on producibility. The Ramsey sandstone of the Bell Canyon Formation was investigated in the Ford Geraldine unit, Culberson and Reeves Counties, Texas. Outcrops of the Bell Canyon Formation in Culberson County, Texas, were studied to better interpret the depositional processes that formed the reservoirs at the Ford Geraldine unit and to determine the dimensions of reservoir sandstone bodies.

On the basis of core descriptions, subsurface mapping, and the depositional model developed from outcrop, the 0-to 60-ft-thick (0- to 18-m) Ramsey sandstone interval in the Ford Geraldine unit was interpreted to consist of sheetlike turbidite lobe deposits overlain and incised by channel and levee deposits. Because of the narrow range of grain sizes in Ramsey sandstones and the absence of detrital clay, log patterns are generally not diagnostic of facies. Comparison of sedimentary structures viewed in core to facies identified in outcrop was key to interpreting the reservoir facies. Lobe deposits consist of massive and convoluted sandstones that have load and dewatering structures, suggesting that the sandstones were deposited rapidly from high-density turbidity currents. Channel facies, which are approximately 1,200 ft (370 m) wide and 15 to 35 ft (5 to 10 m) thick, overlie and locally incise the lobe deposits. They consist of massive and crossbedded sandstones interpreted to have been deposited from high-density turbidity currents. Channel margins, characterized by rippled and convoluted sandstones interbedded with siltstones, are interpreted as channel levees formed by overbanking of low-density turbidity currents. The levees are onlapped by massive sandstones interpreted as interchannel lobes or splays. Ramsey sandstones are bounded by laterally continuous, organic-rich siltstones deposited by settling from suspension. Siltstone beds and extensively calcite cemented sandstones are the most important causes of reservoir complexity and reduced sweep efficiency.

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