Geologic Analysis of Primary and Secondary Tight Gas Sand Objectives, Phase C

Previous assessments of blanket-geometry tight gas sandstones led to the selection of the Travis Peak Formation of the East Texas and North Louisiana Basins and the Corcoran and Cozzette Sandstones of the Piceance Creek Basin as major research objectives. The anticipated outcomes of this study include increased availability of tight gas resources and advancements in technology with high transferability. The work reported here encompasses all aspects of the depositional systems and reservoir geology of these units as fundamental components of resource characterization, with an emphasis on understanding controls on reservoir facies distribution and their relevance to low-permeability reservoir development.

Six lithofacies of the Travis Peak (Hosston) Formation in East Texas and North Louisiana have been identified using electric logs. These facies comprise sand-rich fluvial-deltaic, silt-rich delta-front, clay- and carbonate-rich shelf, carbonate reef, and clay-rich open marine facies. The most well-developed facies in the East Texas area are the fluvial-deltaic and delta-front facies. Travis Peak rocks from the Clayton Williams #11 Sam Hughes well, Panola County, Texas, were primarily deposited in a fluvial environment within a coastal plain setting. Porosity and permeability control in the clean sandstones are primarily attributed to quartz overgrowths, chlorite cement, and solid organic matter, with approximately half of the remaining porosity being secondary, resulting from framework grain dissolution.

Studies of Travis Peak gas production at Pinehill Southeast and Percy-Wheeler fields indicate an average permeability-thickness product of about 10 md-ft, with a range of 0.7 to 35 md-ft, indicating dry gas reservoirs. Well logs, core, and mud logs from Chapel Hill field in Smith County, Texas, were examined in preparation for a complete cooperative well program in the ARCO #11 Phillips well on the western margin of that field.

Field studies of Corcoran-Cozzette Sandstones near Grand Junction, Colorado, suggest that the depositional environments of the Corcoran evolved from marine upper shoreface to non-marine, while the Cozzette sequence evolved from lower to upper shoreface. Porosity and water saturation calculations have been conducted by computer for seven Corcoran and Cozzette depositional units. A comparison of calculated water saturation with core-derived porosity and permeability indicates a fair to very good correlation of reservoir properties with clay content measured by gamma-ray log.