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Abstract: Using NMR-Derived Effective Permeabilities To Predict Production Results in Tight Gas Sands, East Texas Basin

SCHMIDT, KEVIN W., RICHARD T. SVOR, RICHARD S. LEONARD, RAY N. WALKER, and NICOLE V. BOLAY, Union Pacific Resources

Union Pacific Resources has developed a simple model, based on NMR log response, that qualitatively predicts economic vs. uneconomic production. The model was specifically designed for use in the Cotton Valley and Travis Peak tight gas formations of the East Texas Basin. Rather than relying on core and laboratory measurements, actual production results from over 50 wells were used to calibrate calculated effective permeabilities to gas and water. These permeabilities form the basis for an interpretation that predicts production on an interval-by-interval basis. During the eighteen-month process of building a database of NMR logs and production results, the model iteratively was fine-tuned until its predictive capabilities had been clearly demonstrated.

The NMR model was then made an active component of subsequent completion decisions. Since its incorporation into the completion process, UPR's success rate at choosing economic intervals to complete has doubled. Interpretations based on the model are 90-95% accurate when predicting poor production. The avoidance of completing in these poor intervals has not only significantly reduced completion costs, but has also lowered water production and its associated expenses. Gas volumes have not been negatively affected by the new, more selective, approach to completions. Additional savings were realized by eliminating density, neutron, and sonic porosity tools from the logging suite, allowing NMR to be run at a minimal incremental cost.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah