Pore Characteristics as Surrogates for Permeability in Mapping Reservoir Flow Units: Vacuum San Andres Field, Lea County, New Mexico

AHR, WAYNE M., Texas A & M University, College Station, TX

A study of the Vacuum San Andres field reveals that porosity and permeability in this anhydritic dolomite reservoir are not limited by facies boundaries. Processes of early dolomitization followed by leaching created a mainly diagenetic pore system with five fundamental pore types: (1) intercrystalline; (2) intergranular; (3) intragranular; (4) moldic; and (5) vuggy. Percent porosity, from core analyses and derived from borehole logs, was mapped by dividing the San Andres Formation within the field into 20 slices of 20 ft each. Average porosity for each slice was contoured by computer and spot-checked by hand contouring. Sectors with porosity less than 6%, 6-12%, 12-18%, and greater than 18% were hand-colored to form a 4-dimensional map of percent porosity in space. The maps for each lice were stacked to create a physical model of field-wide porosity distribution. Measurements of pore dimensions in each pore category in each thin section were made to determine the distribution of mean pore size by type in each percent-porosity sector. Mean pore size was plotted against permeability to test for correspondence. The distribution of pore types and sizes within each percent-porosity sector was compared with core lith logs and with values from borehole logs to identify co-variant pore, rock, and borehole log properties with which to construct a flow-unit map. The flow units are thereby defined by using pore characteristics as surrogates for permeability and by using the correspondence between rock type and pore properties to extend mapping capabilities beyond cored wells a an aid in reservoir characterization for enhanced oil recovery.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)