Abstract

Wolfcamp production in many Central Basin Platform fields, including DEB Field (1952), has long been attributed to porosity developed within reefs or buildups. Field development and waterflood implementation assumed all significant structural movement ceased prior to Wolfcamp time with no faults cutting the Wolfcamp. Our work at DEB reveals that hydrocarbon production is from stacked carbonate shoal facies. Evaluation of 3D seismic, core and tracer surveys have revealed some faults cutting through the Wolfcamp section that may be impacting waterflood performance. However, the water cycling issue could be contributed to a number of other factors including the underlying porous buildup facies, waterflood implementation, and reservoir and rock parameters. To better understand the field performance Whiting has done core descriptions, log-core calibrations, special core analysis, tracer surveys, and injection profiles.

Two cores (over 600’) were described in detail yielding eight depositional facies (from deepest marine to shallow platform interior): 1. crinoidal lime wackestone; 2. crinoidal-fusulinid lime wacke/packstone; 3. bioclastic-intraclastic-skeletal lime wacke/packstone; 4. bioclastic lime packstone; 5. bryozoan-fusulinid-platy algae lime bound-stone; 6. coarse-grained, skeletal lime pack/grainstone; 7. coarse-grained fusulinid-bioclastic-coated grain lime pack/grainstone and grainstone; and 8. foram-dasyclad-peloid lime packstone. Main pay facies 6 and 7 were deposited as aggradational, high energy platform-margin shoal complexes. Significant porosity and permeability also occurs in facies 5 boundstones, positioned about 40-50’ below the main pay zone in the water leg. A reciprocal relationship exists between the development of facies 5 buildups and overlying shoals - where the buildup is thick and well-developed, shoal pay facies are thinner. The most extensively developed buildups experienced significant secondary porosity development, resulting in a well-connected network of vugs, cavities, and solution-enlarged fractures that could contribute to excessive water production through coning.

Log correlations of cycles are challenging, but key surfaces and stacking patterns defined through core and tied to 3D seismic & image logs assist in uncored areas. Facies recognized from the core can be correlated to image log. Five of the eight facies are readily recognized on the image logs. This can be useful in carrying flow units around the field and providing more robust porosity-permeability relationships. This has been done to better understand the reservoir and flow architecture throughout the field.