ABSTRACT

Vertical and horizontal transects were sampled from core and outcrop of the San Andres Formation at Lawyer Canyon, Guadalupe Mountains, New Mexico, to assess permeability variation in a geologic framework of upward-shallowing carbonate cycles and to show the potential effect these variations have on viscous-dominated flow behavior in analogous reservoirs. These cycles occur in a ramp-crest facies tract, are 3–13 m (10–45 ft) thick, and contain both vertical and lateral variation of lithofacies. Thicker cycles consist of a basal dolomudstone, which is overlain by burrowed dolopackstone, and capped by bar-flank ooid-peloid dolograinstone and bar-crest ooid dolograinstones.

In vertical transects, permeability is extremely variable about the mean, yet upward-increasing trends coinciding with the succession of lithofacies typify a given cycle. Semi-variance analysis shows permeability to be uncorrelated vertically at distances greater than 5.5 m (18 ft), which is the average cycle thickness, suggesting that the cycles may equate to a fluid-flow unit in a reservoir. Semi-variance analysis of measurements collected along a horizontal transect within bar-crest dolograinstones of a single cycle shows permeability is uncorrelated at distances greater than 3.6 m (12 ft). This correlation distance appears to be controlled by alternating porous and tightly cemented zones that formed during dolomitization.

Vertical and lateral variogram models were fit to the spatial parameters to generate a variety of conditionally simulated permeability fields. Fluid-flow simulations show viscous-dominated flow behavior is compartmentalized by both the individual cycles and groups of cycles. The basal dolomudstones are potential baffles to flow crossover between cycles, but poorly developed cycles (i.e., those that are mud rich and lack well-developed bar-flank and bar-crest facies) result in the greatest compartmentalization of fluid flow within a succession of cycles.

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