Recoverable Resource Estimate of Identified Onshore Geopressured Geothermal Energy in Texas and Louisiana
Geopressured geothermal reservoirs are characterized by high temperatures and high pressures with correspondingly large quantities of dissolved methane. Due to these characteristics, the reservoirs provide two sources of energy: chemical energy from the recovered methane, and thermal energy from the recovered fluid at temperatures high enough to operate a binary power plant for electricity production. Formations with the greatest potential for recoverable energy are located in the gulf coastal region of Texas and Louisiana where significantly overpressured and hot formations are abundant. This study estimates the total recoverable onshore geopressured geothermal resource for identified sites in Texas and Louisiana. In this study a geopressured geothermal resource is defined as a brine reservoir with fluid temperature greater than 212 °F and a pressure gradient greater than 0.7 psi/ft.
First, the total thermal resource in place for the geopressured regions considered was estimated based on the temperature and volume of the geopressured reservoir fluid. Geopressured reservoir fluid volume was estimated utilizing data on the depth to geopressure, average porosity, and sand and shale thickness collected from multiple sources on geopressured reservoirs in the Gulf Coast. Temperature was estimated using over 6,000 corrected bottomhole temperature measurements from wells located in the identified areas and interpolated to the midpoint depth of the geopressured reservoir interval.
Next, fluid recovery factors for the geopressured reservoirs were determined. The recovery factors in the Frio and Wilcox reservoirs in Texas were based on multiphase flow reservoir modeling and a minimum flow rate of 10,000 bpd. The recovery factors in Louisiana were based on a single well radial flow model and a maximum reservoir pressure decline to maintain unaided flow. Fluid recovery factors from the sandstone layers range from less than 1% to 15% depending on thickness, permeability, reservoir continuity, and fluid overpressure. Using these recovery factors for each region, the total recoverable resource and the resource temperature distribution is calculated. The study identified regions with high temperatures and recoverability factors corresponding to high fluid and thermal flow rates that may be developed first for energy production.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California