South Texas Frio Sandstones Regional Study


This project was designed to optimize operators’ exploitation of down-dip, geopressured, Frio gas reservoirs in south Texas. Operators in this trend indicate that are having problems in the formation evaluation, well completion, stimulation and production aspects of down-dip Frio gas wells. These problems include but are not limited to the following:

  • Recognition of pay versus non-pay (low-resistivity contrast) as a result of pore system clays, shaly bioturbated reservoirs, and/or thin-bedded reservoirs
  • Petrophysical evaluation and reserve estimates
  • Prediction of permeability for the assessment of formation damage and production performance
  • Casing collapse associated with rock compressive strength failure after fracture stimulation and drawdown
  • Rock-fluid compatibility, well completion and stimulation designs
  • Reduced permeability and porosity associated with pore volume compressibility during production

These problems have cost companies millions of dollars and can only be solved from the geological, petrophysical and geomechanical analysis and evaluation of either conventional cores or rotary sidewall cores. Cores from sixteen (16) wells were thoroughly analyzed in this fashion. The resultant data was used to calibrate open-hole logs and dipole sonic logs (e.g. MAC) in order to better predict rock types and properties essential for formation evaluation and proper well completion and stimulation designs. These rock types and their measured petrophysical and geomechanical properties serve as analogs when evaluating new reservoirs in wildcats or field step-outs.