Opportunities for Horizontal Drilling in Texas

FINLEY, ROBERT J., S. E. LAUBACH, NOEL TYLER, and M. H. HOLTZ, Bureau of Economic Geology, University of Texas at Austin, Austin, TX

To date, horizontal drilling in Texas has been effective in achieving production increases where natural fracturing is significant, as in the Pearsall field of the Austin Chalk trend of south Texas. Projected average ultimate recoveries of 500,000 bbl of oil and 500 mmcf of gas per horizontal well compare with 75,000 bbl and 82 mmcf for vertical wells in that field. In addition to increasing production from naturally fractured reservoirs, horizontal drilling applications can enhance production where coning problems exist, where the reservoir zone is thin, where a gravity drainage mechanism exists, or where macroscale heterogeneity can be overcome to produce from complex, compartmentalized reservoirs.

Major Texas reservoirs have been classified into 47 oil plays and 73 gas plays that are useful in evaluating the application of horizontal drilling. Geologic character amenable to horizontal drilling is evident in at least 10 oil plays containing 144 reservoirs, more than two Bbbl of proved reserves, and eight Bbbl of unrecovered mobile oil. These plays include, for example, Austin/Buda Fractured Chalk, Caddo Reef, San Andres/Grayburg Carbonate, Upper Pennsylvanian Slope Sandstone, and Spraberry/Dean Fan Sandstone.

At least seven gas plays containing more than 124 reservoirs with cumulative production of more than 19.7 tcf are amenable to horizontal drilling. Tight gas reservoirs may benefit from multiple hydraulic fracture treatments from horizontal well sections drilled parallel to the minimum horizontal stress direction. Gas plays amenable to horizontal drilling in Texas include Lower Cretaceous-Jurassic Sandstone, Sabine Uplift Area; Upper Pennsylvanian and Lower Permian Slope and Basinal Sandstone; Wolfcamp Carbonate; and parts of the Lower and Middle Pennsylvanian Fan-Delta Sandstone and Conglomerate. Although play analysis defines general suitability, applications of horizontal drilling depend upon geologic, engineering, and, most importantly, economic assessments of specific prospects. I creased understanding of fractured reservoirs and of scales of reservoir heterogeneity will enhance future applications.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)