ABSTRACT: Test Results of the Geopressured-Geothermal Resource in South Louisiana

Michael Byron Miller, Chacko J. John

The U.S. Department of Energy (DOE) initiated a program in 1975 to evaluate the geopressured geothermal resource in the northern Gulf of Mexico basin. Geopressured reservoirs (>0.7 psi/ft) capable of flowing methane saturated brines at temperatures of 300°F are an alternative energy resource. The U.S. DOE sponsored nine geopressured geothermal test wells in Louisiana: six wells of opportunity (WOO) were abandoned hydrocarbon exploration wells, re-entered to test geopressured reservoirs; three design wells were drilled specifically for long-duration flow tests of selected geopressured geothermal prospects. The WOO program provided short-duration flow tests over a broad sample of geopressured reservoirs.

Maximum brine flow rates for the test wells range from 3887 to 36,500 bbl/day. Flow rates of 50,000 bbl/day are expected with larger production tubing. Formation brine temperatures range from 234 to 330°F. Brine salinity is variable from 23,500 to 190,904 ppm total dissolved solids. Brine solution gas values are 20-50 scf/bbl. Gas composition is primarily methane (71-94 mole %) and CO₂ (2.5 to 23.5 mole %). CO₂ content increases with temperature, resulting in a decrease in methane. Several wells recovered minor amounts of liquid hydrocarbons during brine production, the origin of which is not known. Recovered brines appear gas saturated. Although undersaturated brines were reported from three wells, liquid hydrocarbons and CO₂ depress methane solu ility, possibly to saturation levels.

Formation water expansion is the principal reservoir drive mechanism. Rock compressibility and additional drive mechanisms contribute locally. Resource utilization is potentially feasible with the combined application of methane, hydraulic, and geothermal energy.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990