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| CSG is a natural gas formed as a by-product during the coalification process whereby organic matter is turned into coal. The Sydney Basin, covering Sydney, Wollongong and Newcastle, holds an enormous coal resource and, therefore, potentially vast amounts of CSG. To extract the gas a hole is drilled down into the coal seam and is cased. The Coal Seam is perforated which then enables the gas to flow to the surface, where it is gathered and processed as required.
Unlike conventional natural gas reservoirs, where gas is trapped in the pores or void spaces of a rock such as sandstone or limestone, methane trapped in coal is adsorbed onto the coal surface (cleats and joints) or micropores and held in place by reservoir and (water) pressure. Hence the coal is the source and the reservoir for the methane. The micropore surface area of coal is very large, and can potentially hold significantly more methane per unit volume than most conventional reservoirs, making the Sydney Basin's coal seams an excellent source of fuel and energy. The amount of gas trapped in the coal is a function of coal rank, pressure and temperature.
Coal generally has lower permeabilities than conventional reservoirs so the rates of production are usually lower. In order to achieve optimal production rates, one method used is to stimulate the coal reservoirs by hydraulic fracturing. Newer drilling techniques like surface to in-seam (SIS) make fracturing unnecessary and also increase productivity.
CSG is naturally an odourless gas that is used just like any other form of conventional gas to power water heaters, stoves, space heaters in both domestic and business settings and as a direct source of power for industry and as a fuel for electricity generation. Pipeline gas only has an odour due to an odorous additive that is required by law to be included for the purpose of detection. |
| | Drilling, cementing, and extracting CSG | |
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| In order to produce CSG, a well is typically drilled to a depth of between 500m–1,000m to intersect the gas bearing coal seams. Steel casing is cemented into the well bore to isolate the hole from all surrounding stratigraphy and to seal it from the surrounding environment. The casing is then perforated at the depth of the coal seam, to further isolate the gas extraction zone.
Hydraulic fracture stimulation (fraccing) is where a sand and water mixture is pumped into the coal seam through the perforations at the target zone at high pressure until the coal structurally cracks. Fractures propagate horizontally from the well bore, typically in two directions. These fractures, deep in the coal seam, have no effect on the ground surface. The injected sand is used as a proppant to prevent the fractures from fully closing. Essentially the sand is squashed by the coal seam and the sand in the coal establishes a porous pathway, enabling previously trapped gas to flow into the well bore. |
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After the fracture stimulation, a work-over rig installs production tubing in the well, a pump (if required) and surface facilities (well head, piping and instrumentation, etc). The water pump may be required for a short time to extract excess water from the coal seam.
The gas extracted from a completed well that is in production flows through a gathering line network, under its own pressure. Gathering lines are typically located along the boundaries of any properties or roadways to minimise the impact on other surface activities.
The gas produced is then sold to various gas wholesalers and end users in the Sydney market area, as a clean and efficient source of energy. |
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Gas production is dependent on many factors. These typically include the thickness of coal gas content, permeability (ability for the gas to flow), depth of the coal seam and purity of the gas. CSG in the Camden region of the Sydney Basin typically contains over 95% methane. Therefore, it generally requires less processing than conventional gas.
CSG is typically found at depths ranging between 400m – 1,000m. These shallower depths make it possible to use smaller, more mobile, truck-mounted drilling rigs than those used for conventional gas. This reduces the surface foot print of the activity and improves exploration cost efficiencies. |
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SGL uses proven CSG drilling, extraction and production technology. That technology is constantly being developed and refined through collaborative research with the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the School of Petroleum Engineering, The University of New South Wales (SCOPE). SGL is an innovative, technically driven company. |
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