Mid-Max Field: A Piece of the Silurian-Devonian Exploration Puzzle

Abstract

The Mid-Max field, Andrews County, Texas, provides an example for the exploration and development of subtle stratigraphic targets in the Permian basin. The integration of all available data, including seismic, log, core, and engineering data, is essential in this mature area as the search for hydrocarbons turns toward subtle structural and stratigraphic prospects. The Mid-Max field, on the Central basin platform, is a Silurian reef. Seismic data support the geologic interpreation of Woodford Shale thinning over a Silurian high, a Silurian to Fusselman thick, and the presence of a relatively flat Fusselman reflector beneath the Silurian high. Whole cores and rotary sidewall cores from the field contain stromatoporoids, corals, algal stromatolites, crinoidal grainstones and other reef elements. The reservoir is predominantly dolomite with porosity and permeability being variable and controlled by the presence of lime mud, fracturing, and diagenesis. The 26-29 API gravity sour crude produced at Mid-Max field is atypical of Siluria-Devonian oils, which commonly are sweet crudes of 35 to 45 API gravity. This atypical oil is explained by the mixing of two types of Woodford-sourced oils and biodegradation. Tectonism appears to have played a minor role in the formation of the Mid-Max field, unlike the conventional faulted-anticlinemore » prospects in the Silurian-Devonian of the Permian basin. Although modern common-depth-point seismic data and a dry Silurian test exited over the Mid-Max prospect prior to drilling, these illusive traps commonly are misinterpreted or overlooked, which would suggest that there might be similar subtle Silurian prospects elsewhere in the Permian basin.« less