Outcrop-Based Reservoir Architecture of the Mixed Carbonate-Siliciclastic Grayburg Formation, Guadalupe Mountains, Permian Basin

Lindsay, Robert F.^1
1 Geological Technical Services Division, Saudi Aramco, Dhahran, Saudi Arabia.

Outcrop studies of the Permian (Guadalupian) Grayburg Formation, a mixed carbonate (dominant)-siliciclastic (subordinate) sequence deposited upon a ramp, in the Guadalupe Mountains on the west and east sides of the Queen Plateau were used to create a sequence stratigraphic model that could be applied to Grayburg reservoirs in the Permian Basin, a distance of 160 km (100 miles) and 290 km (180 miles) east of the outcrops.

These studies helped improve and constrain sequence stratigraphic models and assisted in the understanding of potential reservoir architecture. In outcrop, and in subsurface oil fields, difficulty in understanding reservoir architecture had to be addressed to explain the dramatic increased reservoir thickness down-dip into the basin. These efforts proved fruitful and contributed significantly to revised sequence stratigraphic models, and successive updates dramatically improved the understanding of potential reservoir architecture.

Carbonate lithofacies, though dolomitized, were easily identified, with lower Grayburg lithofacies transgressively dominated and upper Grayburg lithofacies highstand dominated. Exposure surfaces are common up-dip, while conformable surfaces are common down-dip. Most of the Grayburg succession experienced erosion so that the outermost part of the ramp was lost. Siliciclastics were found to have been stranded on the ramp where they are preserved in paleogeographic lows. Outcrop studies provided 97 measured sections and information on carbonate and siliciclastic lithofacies distribution, position of exposure and conformable surfaces, and cyclicity on all scales, from individual beds, approximately 80 carbonate cycles (parasequences), cycle sets (parasequence sets), 10 high frequency sequences, two simple sequences, and one composite sequence.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009