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Gulf of Mexico Onshore
GEOLOGICAL, PETROPHYSICAL, AND ENGINEERING STUDY OF THE LOBO (LOWER WILCOX) SANDSTONES WEBB AND ZAPATA COUNTIES, TEXAS - Available in RAPID
Core Laboratories initiated this study to address problems related to exploration, reservoir evaluation, exploitation and completion of Lobo sandstone reservoirs. The objective of the study was to provide participating companies with detailed geological, petrophysical, and engineering characterization, and evaluation of productive and potentially productive reservoir sandstones on both a local (field) and regional scale.
There are twenty-four (24) project wells with the majority of these wells located in Webb County. Of the twenty-four (24) project wells, thirteen (13) contain conventional cores that comprised 2,117 feet of Lobo section. The Lobo sandstones in the remaining eleven wells were represented by either sidewall cores or drill cuttings.Cored Lobo sequences were analyzed in terms of lithology, sedimentary structures, vertical sequence, and depositional environments. Depositional environments for wells with only sidewall cores or drill cuttings are also interpreted based on gamma-ray log signatures, petrographic criteria, and comparison to conventional core analogs.
Reservoir sandstone properties such as texture, mineralogy, diagenesis and pore structure were determined petrographically. Special emphasis was directed at both depositional and diagenetic controls on reservoir quality and the influence of clays on petrophysical properties and log response.
Detailed petrophysical measurements and evaluations of sandstone reservoir parameters were performed. These include porosity, permeability, grain density, porosity and gas permeability as a function of overburden pressure, electrical properties, effective gas permeability, immobile water saturation, and capillary pressure. Each zone that was geologically evaluated in a particular well was also evaluated petrophysically by log analysis. Log-derived petrophysical properties were then compared to core analysis data where available.
Each of the project wells was evaluated by a well completion engineer in order to assess drilling and completion procedures and potential formation damage problems. In addition several drilling, completion and fracturing fluids used by operators in the trend were tested for their "compatibility" with Lobo reservoir sandstones.
The generated data and interpretations for the project wells are provided in three comprehensive Well Summary Reports. A final report provides a summary and regional synthesis of the geological, petrophysical and engineering aspects of the Lobo Reservoir sandstones.