In a producing natural gas well, a wellhead is placed on the surface to maintain control of the well and the well is pressure-tested to ensure that it is safe.
The wellhead contains barriers, valves, seals and a gas/water separator. It allows the pressure of the well and the flow of fluids to be controlled at the surface.
Gas is held in coal seams by burial pressure and water. When water is pumped out of the coal seam, total pressure falls and the gas begins to be released. Generally, gas production cannot begin until dewatering of a coal seam has begun.
CSG production extracts water from coal seams rather than from normal aquifers.
Water in coal seams is usually 200 metres or more below the water table used for stock and domestic purposes.
It is distinct from water found in other non-coal seam aquifers and has different properties to normal artesian water. CSG production water tends to be relatively saline (usually it is brackish, like estuarine water).
By using horizontal drilling and hydraulic fracturing, a single gas well can tap a large area, reducing the need for surface infrastructure. Horizontal drilling also allows several wells to be drilled from the one surface location.
Once the land at the wellsite has been restored, a small cleared area remains around the well-head. A CSG well-head and associated infrastructure is smaller than an average water tank and the fenced off area around the well is typically slightly larger than a tennis court.
Wells usually produce gas for many years with little surface activity other than regular environmental checks.
Getting gas to markets
The well will be connected to a pipeline so gas can be transported to markets. This requires either building a new pipeline or connecting the well to an existing pipeline.
Gas can be used within Australia for electricity generation, household gas and industrial uses.
It can also be sold into export markets as liquefied natural gas (LNG).
LNG plants super-chill the gas to liquefy it. LNG’s volume shrinks to 1/600 of the space taken by natural gas in its gaseous form, enabling export via purpose-built tankers.