John M. Layman1
(1) Texas A&M Universtiy, College Station, TX
ABSTRACT: Pore Measurements by Petrographic Image Analysis: Implications for Rapid Identification and Ranking of Reservoir Flow Units, Happy Spraberry Field, Garza County, Texas
The Spraberry Formation (Permian, Leonardian) typically produces from turbidite deposits in the central Midland basin. At Happy Spraberry Field, Garza County, Texas, however, production is from a carbonate interval about 100 feet in thickness. The section is interpreted as shallow-shelf carbonate deposits of the Clear Fork Formation, time-equivalent to Spraberry basinal siliciclastics. Lithologies present in the field include oolitic/peloidal grainstones and packstones, rudstones and floatstones, in situ Tubiphytes boundstone, and laminated to rippled, very-fine grained siltstones and sandstones. The highest quality reservoir facies are those of oolitic/peloidal grainstones and packstones where grain-moldic and solution-enhanced intergranular porosity dominate. Vuggy and intraparticle also contribute to overall, effective porosity.
The purpose of this study was to relate pore geometries attained and identified by digital petrographic image analysis to petrophysical characteristics and, inherently, to reservoir quality. Image analysis was utilized to determine porosity parameters such as size, shape, frequency, and distribution. This process resulted in an automated technique for identifying pore facies within the reservoir. The best reservoir intervals are directly related to optimum-paired values of porosity and permeability, but only certain genetic pore types and percentages are correlabe to PHI-K values determining pore origin and the percentage each pore type contributes to reservoir-prone facies. The interdependence between pore measurements, pore origin, and petrophysical behavior of the rock is integral to understanding how the porosity complex relates to the geology and architecture of the reservoir.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado