In order to better understand the control exerted by fractures on the recharge and production zones of limestone aquifers, the authors delineated surficial fracture zones in the southern Edwards Plateau, Texas. Lineations were marked on nearly 200 mosaics scale of 1:24,000. Approximately 400 fracture zones were identified on each mosaic.

 Geologic map that depicts the surface geology of Parmer and Castro Counties and parts of Deaf Smith, Randall, Bailey, Lamb, and Hale Counties.

Reservoir quality of lower Teritary sandstone reservoirs along the Texas Gulf Coast is controlled by sandstone depositional environment, mineralogical composition, and consolidation history (compaction, cementation, and leaching). In general, shallow reservoirs have primary porosity that is reduced by compaction andcementation, whereas deeperreservoirs result from late subsurface leaching.
Frio sandstones have the following idealized consolidation history:

Disposal and temporary surface storage of spent geothermal fluids and surface subsidence and faulting are the major environmental problems that could arise from geopressured geothermal water production. Geopressured geothermal fluids are moderately to highly saline (8,000 to 72,000 parts per million total dissolved solids) and may contain significant amounts of boron (19 to 42 parts per million). Disposal of hot saline geothermal water in subsurface saline aquifers will present the least hazard to the environment.