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.

This report documents research done on the mature and prolific McAllen Ranch gas field in South Texas, as part of the Secondary Gas Recovery (SGR) project funded by the Gas Research Institute, U.S. Department of Energy, and State of Texas.ABSTRACTA Secondary Gas Recovery project study in South Texas demonstrated that reservoir compartmentalization can result in reserve growth in a mature gas field. McAllen Ranch is an important field in that it typifies South Texas gas fields that produce from the deep, overpressured sandstone reservoirs of the Oligocene Vicksburg Formation.