Abstract: Preliminary Quantification of Adsorbed Gas in Monterey Shale Reservoirs at Elk Hills, Kern County, California

MCINTYRE, JANA L, THOMAS J. HAMPTON, STEPHEN A REID, MARK L WILSON, TERRY W. THOMPSON, and KEITH H. GREAVES

Cumulative gas production from Monterey Shale reservoirs at Elk Hills exceeds values predicted by material balance and simulation. One possible source of this additional gas is the release (desorption) of gases adsorbed onto organic material and clays as reservoir pressure drops. Desorption and adsorption analyses were performed on new core from three shale reservoirs to estimate the contribution of desorbed gas to total production.

Desorption analyses (to atmospheric pressure) resulted in fatal gas yields ranging from 172 to 377 mcf per acre-foot for the three reservoirs. Total gas yields include desorbed, solution, and free gas components. Methane adsorption isotherm analysis for two of the reservoirs indicates that 14 to 37 percent of the total gas yield may be attributed to desorbed gas. Preliminary gas modeling, which incorporates data from methane, ethane, and propane adsorption isotherms, suggests that percentage may be higher. For methane adsorption isotherms only, the decline in reservoir pressure over the last twenty years indicates that between 5.6 and 15.5 mcf per acre-foot has already desorbed from Elk Hills shale reservoirs.

Additional analytical work is planned that will more accurately quantify the remaining adsorbed gas resource at Elk Hills. Results could impact completion design, pressure maintenance strategies, and development drilling at EIk Hills and other California fields with similar shale reservoirs.

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