Graham E. Fogg

Outcrop/Subsurface Comparisons of Heterogeneity in the San Andres Formation

An integrated outcrop and subsurface study of permeability variations in the San Andres formation demonstrates the extreme heterogeneity present in this economically important carbonate horizon. Permeability measurements were made with a field permeameter and were compared to subsurface core data. Geostatistical techniques were used to predict variability and scales of spatial correlation. Measured permeability showed substantial variability within units arranged in three correlation scales. Outcrop permeability data exhibited no marked permeability anisotropy in predicted spatial correlation length. Several scales of spatial variability have been observed in an outcrop section, with subsurface results in agreement.

Geological/Stochastic Mapping of Heterogeneity in a Carbonate Reservoir

Two major problems in estimating interwell porosity and permeability patterns are estimating permeability profiles in uncored wells and interpolating wellbore information between wells. This paper reports on a technique combining core analysis, rock fabrics, and wireline logs used to estimate permeability values at 1-ft intervals in 32 wells in Section 15 of the Dune field. Stochastic geologic interpolation was generated with a geostatistical method known as conditional simulation. Simulation of water-flooding showed that the stochastic realizations with a low degree of continuity gave the most realistic results. Infill drilling to achieve an average well spacing of 2.5 acres increased recovery by 27 to 32%.