Disposal of brackish water concentrate into depleted oil and gas fields: a Texas study

Disposal of concentrate from brackish water desalination plants by deep well injection into oil and gas fields is an attractive option in Texas. Underpressured depleted oil and gas reservoirs cover large areas of the state. Six areas were selected from across Texas for detailed analysis. These sites were characterized by abundant brackish groundwater, a projected shortage of freshwater, depleted oil and gas fields, and shallow injection wells. Information was collected on formation mineralogy, pressure history, geochemical attributes and flow parameters. Numerical modeling using SOLMINEQ, combined with a statistical approach, was used to assess the results of mixing desalination concentrate with formation water. Issues addressed include injection pressures required, the impact of down-hole conditions on mineral precipitation, and mobilisation of formation fines and clays. Numerical modeling found no technical problems outside the range commonly dealt with by the oil and gas industry. In addition, historically, most of the fields have received considerable volume of fresh and/or brackish waters. From a technological standpoint, injection of desalination concentrates into depleted oil or gas fields using existing wells is a highly feasible alternative. A brief look at the economics also suggests that this opportunity is highly advantageous.