ABSTRACT: A Decade of Environmental Monitoring at Geopressured-Geothermal Well Test Sites along the Texas-Louisiana Gulf Coast

Donald A. Stevenson, Chacko J. John, C. G. Groat

The U.S. Department of Energy has designed, completed, and flow tested four geopressured-geothermal wells in the Texas and Louisiana Gulf coastal area. A fifth well located in south Louisiana has also been completed and was scheduled to begin testing in late 1989. To date, these wells have produced over 35 million bbl of hot, pressurized, methane saturated brine. The resource involves stripping methane from the pressurized brine and reinjecting the methane-depleted fluid into shallower unconfined sands through disposal wells. In addition to obtaining valuable production information and a better understanding of the commercial viability of this resource, the program has provided a unique opportunity for evaluating environmental impacts resulting from Gulf Coast geopressure -geothermal resource testing and development.

The primary environmental issues of relevance include potential land-surface subsidence, growth-fault activation, and water quality. Since summer 1980, monitoring programs designed to assess each of these environmental issues have been established at all test well sites before, during, and at least one year after plugging and abandonment of each test well. First-order benchmark networks, tied to the NGS National grid, have been established around each site to monitor potential subsidence. Releveling has taken place roughly every other year for the life of each well. Networks of from four to six continuous recording microearthquake monitoring stations have been deployed around each well to monitor for possible growth-fault activation manifested by induced microearthquake activity. Pote tial groundwater and surface water contamination by geopressured geothermal brines and/or drilling fluids have been extensively monitored throughout the program. A decade of monitoring has revealed minimal long-term detrimental environmental impacts related to fluid production or disposal.

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