Desalination of Produced Water Using Reverse Osmosis
Graciela Morales, Maria Barrufet
Many oil and gas wells, particularly those in mature fields, produce large amounts of brine along with the hydrocarbons. Disposing of the brine can be costly, due to its composition and large volume. For example, in the Permian Basin of West Texas and New Mexico more than 490 million gallons of water per day are produced and reinjected. The prospect of many millions of barrels of produced water from coalbed methane wells planned for the Powder River Basin has complicated development of that resource.
Historically, the oil and gas industry has not promoted on-site water desalination. The reinjection or surface discharge alternatives were much less costly and there was little demand for the water. However, growing demand for fresh water in many areas and the development of lower-cost technologies for removing contaminants from water are beginning to provide compelling arguments for produced brine desalination. The Texas Water Resources Institute (TWRI) at Texas A&M University (TAMU) currently is supporting a multidisciplinary program, led by the Department of Petroleum Engineering to develop technologies to treat produced water and make it safe for use in agriculture and wildlife habitat restoration. The aim of the TAMU project is the development of small-scale, modular, transportable units capable of treating relatively small amounts of brine inexpensively. The team will utilize new technology in solids and oil removal and advances in remote process control to create units exhibiting low maintenance and high reliability in the field. These small scale units will utilize nanofiltration (NF) and reverse osmosis (RO) to remove contaminants from oilfield brines.
Similar pressure-driven membrane filtration equipment installations are widely used in desalination of brackish and seawater and compete successfully with traditional thermal desalination operations. However, if RO is to assume a more prominent role in produced water treatment, there is a need for sound engineering designs adaptable to modular operations.
As one portion of this effort, the TAMU team has developed a static model using parametric curves to allow scale-up of an integrated RO system. They are also developing a dynamic model that will be the basis for a control system and automatic operation. This article provides some basic background on RO systems in general, along with a brief description of the static model.