Well Log Analysis In The Austin Chalk Trend

Past and continuing exploration successes in South Texas focus on the potentially large hydrocarbon reserves in Cretaceous carbonate rocks of low permeability, such as the Austin Chalk formation. In addition, production is frequently encountered in the underlying Eagle ford Shale and/or the Buda Lime. Various logging combinations and interpretation techniques have been investigated, ranging from acoustic fracture detection, dipmeter application, to pulsed neutron logs run in open hole. In other words, modern logging suites and novel log interpretation concepts have been found to be necessary for a reliable evaluation of these most low permeability, but often partially fractured, carbonate reservoirs. A newly developed well log analysis technique provides detailed information on (1) total and secondary porosity, (2) reservoir shaliness, (3) reservoir fluid saturation and fluid density, (4) invasion profile, and (5) cumulative porosity-feet and hydrocarbon-feet. The basic data is obtained with a total of only two logging trips in open hole, specifically the Induction Electrolog - Borehole Compensated Acoustilog (all run on one trip into the hole), and the Gamma Ray - Dual Detector Neutron Lifetime Log. This new reservoir analysis has been incorporated as part of Dresser Atlas' computerized EPI LOG system for converting log measurements to reservoir parameters which can be easily evaluated. Resulting computerized well log analysis assists in engineering and managerial decisions whether or not to run casing and which intervals should be selectively perforated, tested and/or stimulated. As of February, 1977, this recently developed technique has successfully predicted well performance in over 70 boreholes, drilled by various operators in several Texas Counties. Several field cases illustrate these new interpretation concepts, including subsequent well testing results, for the Austin Chalk, Eagleford Shale, and Buda Lime.