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LANCASTER, JAMES R., Evaluations, Inc., Littleton, CO; and JOHN H. DOLLOFF, Ripley Energy Associates, Golden, CO

ABSTRACT: Log Derived Total Organic Carbon is used to Estimate the Gas Storage Capacity of the Lewis Shales, San Juan Basin, New Mexico and the Sand Wash Basin, Colorado

An application of core and sample analysis for determining gas storage capacity from total organic carbon is presented from a study using wireline logs to compute total organic carbon. Results of log-based evaluations are comparable to those determined with a technique using cores and drill cuttings. Data are presented for wells located in the San Juan Basin, New Mexico and the Sand Wash Basin in Colorado. In both basins, the evaluations are of the Late Cretaceous Lewis formation. The well-documented San Juan Basin example is typical of developing gas production from previously unrecognized fractured Lewis Shale intervals.

From petroleum geochemistry using wireline logs, the total organic carbon value is used for computing adsorbed gas in either basin. Using previously published table data; equations were generated to compute gas storage capacity in standard cubic feet per ton from the log based total organic carbon. This presentation includes illustrations of: (1) the technique used to compute total organic carbon and other petroleum geochemical values; (2) the application of the core and drill cuttings technique for computing adsorbed gas from (log) total organic carbon; (3) their combined application to a San Juan Basin well; and (4) their combined application to a Sand Wash Basin well.

Producing gas directly from source rocks in re-completed existing cased well bores in the Sand Wash and other basins may be a viable, low-cost means of increasing gas production.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico