Canyon sandstones form a prolific low-permeability gas play in the Val Verde Basin of southwest Texas. Exploration and development activity is at a high level, but little published information on Canyon geology is available. Although several geographically and stratigraphically distinct "Canyon" intervals (Upper Pennsylvanian-Lower Permian) are productive, our study focused on characterizing the stratigraphy, diagenesis, and natural fractures of Sonora Canyon sandstones in Sutton County and Ozona Canyon sandstones in Crockett County.

The Frio Fluvial-Deltaic Sandstone (Vicksburg Fault Zone) play of South Texas has produced nearly 1 billion barrels (Bbbl) of oil since field development began in the 1940's. More than half of the reservoirs in this depositionally complex play have been abandoned, although large volumes of oil remain.

Shallow-water-platform carbonate reservoirs of Permian age have accounted for more than half of the oil production in the Permian Basin, one of the largest oil-producing regions in the United States. Despite more than 70 yr of production, including advanced primary and secondary development, however, these reservoirs still contain as much as two-thirds of the original oil in place. This low recovery efficiency is linked to an incomplete understanding of the geological and petrophysical heterogeneities of these reservoirs and their controls on fluid flow in the subsurface.