Exploration Concepts for Slope Stratigraphic Traps in Carbonate Strata: Lessons from McKittrick Canyon, Guadalupe Mountains
Alton A. Brown
Consultant, Richardson Texas
As exploration becomes more mature in the greater Permian Basin, subtle stratigraphic traps such as slope carbonates become more favorable exploration targets. The major exploration issues with slope trapping is locating a favorable updip porosity pinchout with economic porosity and adequate sealing. Late Guadalupian slope carbonates and basinal clastics exposed near the mouth of McKittrick Canyon illustrate some of the depositional processes that lead to trap formation and provide concepts that can guide exploration fairway identification from 3D seismic and well data.
McKittrick Canyon exposures indicate the following. (1) Updip pinchout related to depositional dip is more likely to develop in the toe-of-slope and proximal basin facies (where depositional dip is a few degrees or less). True slope facies have too steep of dip for good seal deposition and favorable pinchout orientation. (2) Broad zones of gentle depositional dip are more favorable for basinward transport of reservoir into sealing facies. Such slopes are more likely to develop after periods of rapid slope deposition and least likely to develop after long periods of suspension sedimentation. In general, suspension sedimentation flattens the proximal basin slope, whereas debris cones and mixed carbonate muds and grainy deposits steepen the toe of slope and proximal basin. (3) Grain-filled deepwater carbonate channels of economic size are likely to develop even where carbonate sediments have a line rather than point source. Channels aid basinward transport and provide the best opportunity for isolating the grainy deposits in potential sealing facies. (4) Dolomitization is probably necessary to develop high quality reservoir in most Permian-age slope traps. Most grainy toe-of-slope limestone fabrics in McKittrick Canyon are compacted packstones likely to have poor porosity and worse permeability
AAPG Search and Discover Article #90065©2007 AAPG Southwest Section Meeting, Wichita Falls, Texas