Abstract: Antrim Shale Resource and Reservoir Characterization as an Analog for Diffusion Controlled Gas Production from the Monterey Formation

DECKER, DAVID, and BRUCE J. BILODEAU

Between 1990 and 1995 gas production from organic rich siliceous shales has more than doubled from 136 bcf/year to 300 bcf/year. The increased gas rates and reserves per well have resulted from comprehensive reservoir characterization coupled with advanced stimulation techniques and production practices modified to optimize gas rates from these complex shale reservoirs. Of equal importance, laboratory testing established that gas is released from the shale in a nonlinear function of decreasing reservoir pressure, indicating the critical requirement of producing the shale at a minimum bottom hole pressure before substantial gas rates could be achieved.

Recent geochemical studies integrated with field gas content measurements quantified the relationship between increased gas storage capacity with increasing organic content for the Antrim Shale in Michigan Basin. With a mean of 8% TOC and a shale thickness of 100 feet at depths averaging 1500 feet, yields a gas rich reservoir averaging 16 bcf/mi{2}. By comparison, the organic rich siliceous shales of the Monterey Formation. with TOC values ranging between .40 and 9.16 wt. %, a mean value of 3.80% and thickness of several hundred feet, the Monterey Fm. houses a vast unconventional gas resource. Recent gas content measurements from the Monterey Formation. at Elk Hills and Buena Vista Hills have confirmed that the organic rich shale have measurable sorbed gas. Measured gas contents are respectively 50-100 scf/t and 40-70 scf/t. These gas content values are remarkably consistent with other gas productive shales. Extensive resource and reservoir characterization performed on the Antrim Shale when properly modified should be beneficial to understanding the resource and reservoir characteristics of diffusion controlled gas production from the Monterey Formation.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California