Subsurface study of the Permian Ozona Canyon sandstone in the Val Verde Basin, Block MM, southwest Crockett County, Texas

The Early Permian Ozona Canyon sandstone is a prolific tight-gas zone in the Val Verde Basin of West Texas. The Ozona Canyon sandstone is classified as sublitharenite to litharenite with porosities averaging less than 3 percent and permeabilities less than 0.1 md. A study of the Ozona Canyon interval was conducted in the northern portion of Block MM, Crockett County, Texas. The study utilized net sand isopach maps and gamma ray log facies distribution maps to evaluate the depositional environment and determine potential infill drilling locations within the field.

The Ozona Canyon sandstone was divided into 6 distinct intervals, evaluated individually. The upper Ozona Canyon intervals, A and C, are defined as upper fan deposits based on their isopach trends and log facies and display both channel and lobe and levee characteristics. Middle fan deposits are represented by the Ozona Canyon E and F sands, and are dominated by log facies and sand isopach trends characteristic of channel deposits. Ozona Canyon intervals G and H comprise the lower fan deposits and are distinguished from the upper and middle fan deposits by a hotter gamma ray response and the lack of strong, linear sand trends present in the other Ozona Canyon intervals. The G sand is composed almost entirely of channel log facies, whereas the H sand comprises lobe and levee log facies with virtually no channel log facies.

Mapping of the Ozona Canyon sands increased drilling potential in the Block MM field by defining the thick, channel quality sand zones. After completion of the initial maps in August of 1996, over 60 new wells have been drilled. Some of the wells drilled in 1997 yielded IP values greater than 1000 mcfd, higher than that of wells previously drilled in the Ozona Canyon sandstone. The increase in production is attributed to the correlation established between the sand isopach maps and the log facies distribution maps conducted in this study.