--> ABSTRACT: Geological and Engineering Characterization of a Fracture-Modified Grainstone Reservoir: Taylor-Link West San Andres, Pecos County, Texas, by C. Kerans, G. W. Vander Stoep, F. J. Lucia, and M. P. Parsley; #91030 (2010)

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Geological and Engineering Characterization of a Fracture-Modified Grainstone Reservoir: Taylor-Link West San Andres, Pecos County, Texas

C. Kerans, G. W. Vander Stoep, F. J. Lucia, M. P. Parsley

The Taylor-Link West San Andres field is located on the southern margin of the Central Basin platform, flanking the deep Sheffield channel to the south. Of the 47 million bbl of original oil in place, 10.5 million bbl were recovered during primary production; a secondary (waterflood) program was initiated recently. The 100-ft oil column in this field is contained within a north-trending high-energy grainstone shoal complex capping an upward-shallowing succession of outer-ramp fusulinid wackestones and mollusk-crinoid wackestones. Complicating the relatively simple facies setting of the reservoir is a superimposed karst profile developed during pre-Grayburg exposure of the southern margin of the Central Basin platform. Interparticle porosity in the grainstone is typified b 20-50-md permeability, whereas short, wide-aperture fractures are a second pore type with permeability between 100 and 2,000 md. Local zones of microrhombic dolomite porosity believed associated with the karst development also contribute to the pore system.

Most injected water is cycled through fractures, leaving the majority of unswept oil in matrix (interparticle) pore space. Mapping of matrix permeability was accomplished by establishing petrophysical relationships with data from core plugs rather than whole core in order to avoid the contribution of permeability from fractures. A map of log (Khmatrix) reproduces the outline of the grainstone shoal, whereas maps of log (Khtotal/Khmatrix), which is proportional to log (Khfracture), and Sw appear to indicate areas of high fracture permeability. These data, combined with fracture analysis of cores, may aid planning of profile modification for improved contact of injected water with matrix porosity and remaining mobile oil.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.