Coal seam gas associated water treatment and management—opportunities and limitations

Abstract

Coal seam gas (CSG) is a new major export for Australia. The production of CSG releases a significant amount of brackish water to the surface, known as associated water. Queensland’s Department of Environment and Heritage Protection (DEHP) has predicted that the peak yearly flow of the associated water could range between 100-280 gigalitres (GL) per year. This presents a major challenge to the CSG industry in water and its by-product (brine) management. CSG water quality varies across regions, but is typically high in total dissolved solids, bicarbonate, hardness, and silica. Consequently, CSG water without treatment is unsuitable for beneficial uses. To date, reverse osmosis (RO) desalination processes with suitable pre-treatment steps have been employed to remove elevated salts and other compounds before CSG water can be used beneficially. One type of beneficial reuse of the treated water that has gained acceptance and prominence in recent times is the irrigation of agricultural crops and forestry. RO brine, a highly saline stream, requires a managed response to ensure a socially, environmentally and financially sound outcome. Conventional evaporation in brine ponds is not considered favourably under existing government directions and, consequently, alternative solutions are sought. Thermal processes, such as brine concentrators, have been used in the treatment of CSG RO brine. The resulting high-quality distillate produced by thermal processes can be used in a number of applications along with a greater proportion of water recovered from such processes. This peer-reviewed paper concludes that a thermal process in conjunction with a high-recovery RO membrane plant, configured as a hybrid membrane/thermal configuration, is probably a suitable solution to meet policy direction by improving system recovery as a precursor to advance associated water treatment and brine management. The discussion is generated out of MWH’s experience with CSG water treatment and management processes, which totals a number of significant projects in the CSG industry.

Coal seam gas produced water treatment by ultrafiltration, reverse osmosis and multi-effect distillation: A pilot study

“…As a notable example, Australia has seen some of the most significant CSG developments in the world [4]. Australia is on track to become the world's largest liquefied natural gas (LNG) producer by about 2018 [2].…”

“…The state-of-the-art technology for CSG produced water management currently includes pretreatment (e.g. coagulation, pH adjustment, ultra-(UF) or micro filtration) and reverse osmosis (RO) [4,6,10]. RO can achieve about 75% water recovery, depending on the salinity (hence osmotic pressure) and the fouling potential of the CSG produced water.…”

“…For new developments the use of evaporation basins is unlawful in most states unless there are no alternative solutions. Given the possible leakages of the brine into the environment, regulators in Australia have actively encouraged the CSG industry to phase out the use of evaporation ponds for CSG RO brine storage [4]. This policy has encouraged several recent attempts to develop techniques to reduce the volume and/or to beneficially extract the minerals from CSG RO brine [4,12,13].…”

“…Given the possible leakages of the brine into the environment, regulators in Australia have actively encouraged the CSG industry to phase out the use of evaporation ponds for CSG RO brine storage [4]. This policy has encouraged several recent attempts to develop techniques to reduce the volume and/or to beneficially extract the minerals from CSG RO brine [4,12,13]. A noteworthy example is the recovery of soda ash from the CSG RO brine, which is being developed by Penrice (Penrice Soda Holdings Limited, Australia) in collaboration with GE (General Electric, Australia) and QGC (QGC Pty Limited, Australia).…”

Process design of coal seam gas associated water treatment plants to facilitate beneficial reuse

“…Current estimates indicate that for example, in Queensland, the associated water volume from the CSG sector is 60.5 GL per annum with a predicted maximum volume of 70 to 80 GL per annum [5]. The salt content in the associated water is highly dependent upon the location of the CSG wells and typically ranges from 1,000 to 10,000 mg/L in Queensland [6,7]. Consequently, the associated water is normally not directly applicable for beneficial reuse options such as crop irrigation, livestock watering, dust suppression, aquaculture and drinking water [8].…”