--> Abstract: Permeability and Fluid-Flow Patterns in Variably Cyclic Outer-Ramp Carbonates, San Andres Formation, Guadalupe Mountains, New Mexico, Part 2: Spatial Permeability Distribution and Fluid-Flow Simulation, by R. A. Eisenberg, D. J. Goggin, P. M. Harris, and C. W. Grant; #90987 (1993).

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EISENBERG, RICHARD A., D. J. GOGGIN, P. M. HARRIS, and C. W. GRANT, Chevron Oil Field Research Company, La Habra, CA

ABSTRACT: Permeability and Fluid-Flow Patterns in Variably Cyclic Outer-Ramp Carbonates, San Andres Formation, Guadalupe Mountains, New Mexico, Part 2: Spatial Permeability Distribution and Fluid-Flow Simulation

Vertical and lateral permeability distribution within fusulinid-rich, outer-ramp facies of the middle San Andres Formation in the Guadalupe Mountains, New Mexico, were evaluated from field permeameter and conventional permeability measurements on core plugs taken along vertical and horizontal outcrop traverses and on cores from wells drilled adjacent to the outcrop. Geostatistical models of permeability variation, honoring the geologic and petrophysical data, were constructed as input to a waterflood simulator to understand the interactions between heterogeneity and flow in variably cyclic ramp carbonates.

Variograms constructed from conventional plug analyses of permeability for the vertical outcrop transect contain a significant small-scale signal ("noise"), as seen in the high nugget effect (approximately 50 percent of the overall sample variance), and have correlation ranges less than 15 feet (4.5 meters). Different vertical variogram characteristics are displayed by cyclic and noncyclic portions of the middle San Andres. The noncyclic vertical variograms show ranges in correlation less than 12 feet (3.5 meters) and contain a high nugget. Cyclic vertical variograms contain a similar short range in correlation and display a sine wave pattern or hole effect caused by "in-phase/out-of-phase" correlation of the permeability trends within each of the mud-based cycles. Variograms construc ed for horizontal transect data from three distinct stratigraphic units have nearly identical properties. Overall the ranges of correlation are short (10 to 12 feet; 3 to 3.5 meters) when compared to typical interwell distances, supporting a nearly uncorrelated and highly variable permeability model in these outer-ramp carbonates.

Utilizing observed short ranges of vertical and horizontal correlation and honoring the vertical transect data, cross-sectional, fractal permeability fields were generated and input into a waterflood simulator to investigate the sensitivities of oil recovery and overall processing rate to stratigraphy and cyclicity. Cyclic portions of the section are characterized by early water breakthrough and relatively high vertical sweep efficiencies. Within the noncyclic section, waterflood fronts have a piston- or finger-like profile, and vertical sweep efficiency is generally poorer. This modeling suggests that opportunities may exist for contacting bypassed mobile oil through infill drilling and selective recompletion in San Andres reservoirs in similar depositional settings.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.