Regional domains of the Wilcox Lobo natural gas trend, South Texas


The Wilcox Lobo trend is the major low-permeability natural gas producer of the Texas Gulf Coast, having yielded almost 4 Tcf of gas. In recent years Lobo sandstones have accounted for a significant part of domestic tight-gas production: about 13 percent in 1991, the last year for which figures are available. Development activities are growing, marked by rising production rates, producing wells, and active rigs. The Lobo play is recognized to be among the most structurally complex plays in the Gulf Basin. As a result of submarine slumping and widespread normal faulting, sandstone correlation is hampered, nearly completely obscuring play-wide sandstone patterns. Consequently, although success rates are high, in part owing to deployment of 3-D seismic methods, operators surveyed in this study recognize opportunities for further increases in success rates and cost reductions if regional sandstone patterns and other regional geologic variables could be diagnosed. To that end, this report describes regional geologic domains within the Wilcox Lobo play. The setting of the play near the juncture of the Gulf Coast extensional province and the Cordilleran compressional province of Mexico resulted in development of three domains having contrasts in dominant fault trends, sandstone architecture, composition, and diagenesis. The Cotulla domain to the north and east was influenced by a wide, gradually subsiding shelf and has attributes most similar to other parts of the stable Gulf Basin. The Central domain has transitional attributes and an important imprint of salt tectonics. The Burgos Rim domain to the south was affected by a narrow, tectonically modified shelf. It is the least well-explored part of the play. Production characteristics of the three domains differ. Recognition of Lobo domains provides a framework for subdividing the play, documenting and comparing reservoir properties, and predicting sandstone geometry and composition patterns. It is a first step toward establishing regional sandstone and other reservoir attribute patterns that can help guide site-specific work such as interpreting 3-D seismic data and evaluating completion intervals.


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