Desalination Reject Water, Boon or Bust for Secondary Flooding?

Allan Standen, P.G.¹, Dr. Jean-Philippe Nicot, P.E.², John Coll, P.G.¹, and Robert Ruggiero, P.G.
¹ D. B. Stephens
² Bureau of Economic Geology (BEG)

West Texas has recently struggled with a ten year drought that has caused many municipalities to scramble searching for new water supplies, local ranchers to trim their herd size and local farmers to limit irrigation of their crops. Governor Perry in 2002 issued a directive to the Texas Water Development Board (TWDB) to investigate the statewide potential of desalination of seawater and brackish waters to supplement the state’s depleting surface and groundwater supplies.

Two recent publications have provided critical information to evaluate the feasibility of desalination. The “Brackish Groundwater Manual for Texas Regional Water Planning Groups” by LBG-Guyton & Associates was completed late 2003 and evaluated the distribution and availability of brackish waters throughout the state.

The second publication addresses one of the most difficult problems for land-locked desalination plants, the disposal of the reject water, usually in acre-feet (acre-foot = 326,000 gallons) per day. In late 2004, a preliminary report written cooperatively by the BEG and the TWDB was released titled “Please Pass the Salt: Using Oil Fields for the Disposal of Concentrate from Desalination Plants” became available. This document offers a comprehensive regional analysis of six major oil and gas producing areas of Texas and evaluates pressure-related matters, potential chemical changes during injection, and potential scaling and fine mobilization characteristics of oil and gas fields within these basins as well as regulatory matters.

The presentation will discuss a screening process using GIS to evaluate the disposal of one million gallons (3.06 acre-feet) per day of brine from a hypothetical desalination plant located in Midland, Texas. The screening process will evaluate all major oil and gas fields within a fifteen mile radius of Midland. Variables considered in this presentation will include a comparison of the general stratigraphy of the individual well fields, characteristic injection rates, potential for over-pressurization and possible geochemical mixing and fine mobilization issues within these well fields.