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HILL, DAVID G. and CHARLES R. NELSON, Gas Research Institute, Chicago, Illinois 60631

ABSTRACT: Reservoir Properties of the Upper Cretaceous Lewis Shale: A New Natural Gas Play in the San Juan Basin

The San Juan Basin, located in northwestern New Mexico and southwestern Colorado, is one of the most prolific natural gas producing basins in the U.S. This basin currently produces over 4 Bcf of natural gas per day from roughly 20,000 wells. One opportunity for developing new lowcost, low-risk gas reserves in this basin is the Upper Cretaceous Lewis Shale, a marine shale sequence that contains an estimated 96 Tcf of natural gas resources. The gas flow rates from Lewis Shale completions average between 100 to 200 Mcf per day and generally exhibit very shallow production decline rates. The Lewis Shale is not a stand-alone gas play rather it is being developing through recompletions and commingling production from deeper producing zones. This natural gas play is quite unique because several Lewis Shale properties are strikingly different from those of commercially developed shale gas plays in other U.S. basins. In particular, the total organic carbon content and gas content are much lower whereas the matrix permeability is typically several orders of magnitude greater. This paper presents results from evaluations of petrographic, geochemical, and reservoir properties of the Lewis Shale at the San Juan 32-5 Unit #9R well in Rio Arriba County, New Mexico. After fracture stimulation, the initial gas flow rate from the Lewis Shale interval of this well was 1.2 MMcf per day. The core analysis data indicate that the average rock TOC content is 1.3%, the average rock porosity is approximately 3.0%, and that 88% of total gas-in-place volume is stored as a molecularly sorbed phase within the organic fraction. The proportion of gas stored by sorption progressively decreases with increasing depth due primarily to increasing pressure and decreasing average water saturation with depth.

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