Water Journal : Water Journal May 2012
water in mining refereed paper technical features 72 MAY 2012 water gas and electricity provider with interests in gas and oil exploration, production and power generation. The Moranbah Gas Project (MGP), located in the Bowen Basin region, is already one of the largest operating coal seam gas (CSG) projects in Australia. As Arrow looks to supply gas to the international market, production across its broader Bowen Basin acreage will increase. When Arrow's coal seam gas to liquefied natural gas (LNG) plant is built on Curtis Island off Gladstone, more than a third of the gas will be from Arrow's operations in the Bowen Basin. The gas will be transported to Gladstone through the 600km Arrow Bowen Pipeline Origin Energy runs the largest number of onshore oil and gas production facilities and is Australia's leading developer of coal seam gas for eastern Australian markets. Origin Energy and Shell (formerly Arrow Energy) have more 10% of the gas reserves in Queensland (see Figure 2). The National Water Commission had estimated that more than 7500 gigalitres of water will be extracted by the CSG industry over its half-century life, which is about a third of the average annual flow of the Murray-Darling river system. CSG water usage is expected to reach 300GL a year, which is equivalent to current water demand of Queensland's population. Water produced from CSG wells is usually referred to as Produced Formation Water (PFW). PFW quality will often vary significantly between wells in close proximity. The highest flow rate of water produced from a CSG well is typically in the period immediately after commencement of CSG extraction. Water production will gradually reduce over the life of the CSG well. Disposal of PFW is regulated by the Queensland Government's Coal Seam Gas Water Management Policy. CSG production involves extracting methane from coal seams by reducing groundwater pressure that keeps the methane trapped in the coal (see Figure 3). They use high-pressure pumps to inject a mixture of sand, chemicals and water to fracture the rocks and open cracks (called cleats) present in the coal seams to release natural gas. The methane is extracted by reducing ground pressure, and the by-product of the drilling process is water rich in salts. The amount of salt depends on the location and age of the coal seam. Typically five to eight tonnes of salt every megalitre of water is produced, mostly chloride, sodium and carbonates. One of the preferred management options is to treat water to a level suitable for agriculture, industrial or potable use. The predicted large volume all has to be treated. The most common water treatment is using reverse osmosis (RO) desalination processes, but the pre-treatment strategy applied for any CSG water has to be investigated by using good water science and ensuring that the treatment selection is the best for project -- which usually means the best for the RO membrane selection and production arrangement. RO does produce large volumes of salt and brine as a by-product of CSG extraction. Therefore, CSG water management policy recommends that all salt and brine residues that are not disposed of in the short term, either industrially or by safe injection in an aquifer, should be removed from agricultural areas and local water catchments. Comprehensive water management plans coupled with a proven capacity to implement them in regard to salt and brine disposal are requirements of future CSG project approval. Department of Environmental Management (DERM) typically issues a notice of decision to approve a resource beneficial for CSG water based on the following uses: • Aquaculture; • Coal washing; • Dust suppression; • Industrial use; • Irrigation; • Livestock watering. Raw Water Quality Aquatec-Maxcon was requested to provide an integrated membrane plant to treat the storage dams in the gas field of Chinchilla and Talinga, and Moranbah in Queensland. The plants are designed to have the flexibility to move between different sites to maximise well operation. The design of the RO plant is challenging as it needs to deal with a wide range in Figure 2. Locations of Origin and Arrow CSG plants in Queensland. Figure 3. Schematic of gas extraction.
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