Abstract: Geology of Fractured Austin Chalk and Buda Limestone in South Texas

Wilford Lee Stapp

One of our largest oil fields is being developed by 80 drilling rigs over a 300-mi (480 km) trend, from the Rio Grande into East Texas. The drilling at depths from 2,000 to 11,000 ft (600 to 3,350 m) has been motivated by increased oil prices and the success of the hydrofracturing of the impermeable and low-porosity Austin Chalk and Buda Limestone. The search for oil production is a search for fractures more than for facies changes or structural traps. Narrow zones of brecciated chalk along the slumped side of faults and wider areas where the brittle chalk has been fractured by arching, slumping, stretching, or wrenching have been lucrative. The lack of deeper exploration in most areas has made the presence of structural deformation difficult to determine, but geologic ma ping at various levels and theorizing as to buried anticlines and faults, salt pillows, and basement scarps with attendant wrenching, strain, and subsidence have indicated favorable areas.

AAPG Search and Discovery Article #90967©1977 GCAGS and GC Section SEPM 27th Annual Meeting, Austin, Texas