Learn About Coal Seam Gas
Coal Seam Gas Overview
Coal seam gas mining involves drilling deep into the earth to extract methane held in a coal seam. In order to extract the gas, large volumes of salty water contained in the coal seam need to be brought to the surface.This water is the major waste product from coal seam gas mining. Methods used to extract the gas include hydraulic fracturing or lateral drilling. Both of these methods represent risks to groundwater.
As well as the underground impacts described above, coal seam gas mining has severe surface impacts. It requires large numbers of wells to extract the volumes of gas that are sought – in Queensland in 2010/2011 some 18,600 gas wells were approved. Along with gas wells come roads, pipelines, tracks, compressor stations and water storage ponds – which altogether results in an industry which spreads out across the landscape and carves up rural landscapes into giant industrial zones.
CSG Mining Risks:
There is mounting evidence that CSG mining poses substantial risks. These risks include:
- Depletion and contamination of underground and surface water systems and supplies
- Lack of any safe method of disposal of the large quantities of polluted wastewater brought
to the surface in the extraction process;
- Leaking of methane from wells and pipelines and off-gassing of volatile organic compunds
from wastewater storages and compressor stations;
- Human and animal health impacts from air, water and soil pollution;
- Loss of agricultural land and native vegetation from the large surface footprintof CSG
- Risk of seismic activity from fracking and aquifer re-injection.
Over 25% of NSW is covered by Petroleum Exploration Licences (PELs). Both exploration and production projects have been given the green light, despite evidenced risks, insufficient research and growing community concern abou this industry. Repeated calls by community groups, environment groups and the farmer’s organisations for a moratorium on the coal seam gas industry to allow for comprehensive scientific investigation and analysis of the threats posed by the industry have been gnored by government.
Concern about these risks from landholders and communities across the Northern rivers is why we call for the immediate cessation of all unconventional gas mining activities in the Northern Rivers.
What is CSG and how is it mined?
Coal Seam Gas (CSG) is principally methane found in underground coal seams, where it is trapped by natural water pressure. Similar gas may also be found in other geological formations such as shale deposits and tight sandstone rock formations.
CSG, shale gas and tight sands gas are referred to as ‘unconventional gas’ and should not be confused with so-called ‘natural’ or ‘conventional gas’, which is found in more readily accessible rock reservoirs. These types of gas are refered to as ‘unconventional’ because they require specialised techniques such as fracking to extract commercial quantities of gas.
Figure 1: CSG Extraction Well
The extraction of methane from different unconventional sources uses similar extraction techniques. The gas is accessed by drilling vertically into strata until a deposit is reached, at which point horizontal drilling is likely to occur in order to extend the reach of the well. Horizontal drilling may extend kilometres from a well. Drilling involves the injection of a number of chemicals to optimise drilling efficiency. The bore of the well is lined with concrete to prevent leakage of gas and contaminated water into underground systems. Methane, which is physically trapped in the coal structure with water under pressure, is released by reducing the pressure in the seam. This is initially done by pumping out water – known as ‘produced water’.
Shale and tight gas extraction and a significant proportion of CSG production requires some form of additional ‘stimulation’ to extract gas at a commercially viable rate. Hydraulic fracturing (or fracking) is one common stimulation technique.
A simplistic representation of a vertical CSG well is shown here in Figure 1. However, in most cases, horizontal drilling will also spread from the initial bore hole for several hundred metres, and potentially several kilometres. Figure 1 does not indicate how thin and fragile the drill line is in relation to its length. Further, it does not show the many fissures and fractures in the surrounding rock, into which concrete can be lost when the casing is being cemented. These gaps and fractures can make it extremely difficult, and in some cases almost impossible to completely seal the casing.
What is fracking?
Hydraulic fracturing or ‘fracking’ is a stimulation process used in CSG mining. It involves the high-pressure injection of large volumes of water, sand and undisclosed chemicals into the ground to fracture coal. Fracking expands cracks in coal seams, which allows gas to flow much faster and from a wider area. Originally used to tap deep earth oil and gas formations, the use of fracking has been expanded to coal seams, which sit much closer to the surface. This brings contaminated water and geological disruption close to water catchments and aquifers, and the above ground natural and built environment.
Fracking has been directly linked to a considerable number of serious environmental incidents including water contamination, earthquakes and fire. The process is already banned in France and other countries, including parts of the USA.
Chemicals used in fracking
A 2011 submission to the US Congress identified over 750 different chemicals and compounds that are known to have been used in fracking. Most are not disclosed by operators and none of have yet undergone CSG hazard testing and clearance. The following is a partial list of additives that are used in fracturing operations, as indicated by the New York State Department of Environmental Conservation.
Classes of Additives
|Acid||Facilitates entry into rock formations||hydrochloric acid|
|Biocides||Kill bacteria and reduce risk of fouling||glutaraldehyde, 2,2 Dibromo-3-nitrilopropionamide|
|Breaker||Facilitate proppant entry||peroxodisulfates|
|Clay stabilizer||Clay stabilization||salts, ie tetramethylammonium chloride|
|Corrosion inhibitor||Well maintenance||methanol|
|Crosslinker||Facilitate proppant entry|
|Friction reducers||Improve surface pressure||potassium hydroxide|
|Gelling agents||Proppant placement||sodium acrylate, polyacrylamide|
|Iron control||Well maintenance||citric acid, thioglycolic acid|
|Scale inhibitor||Prevention of precipitation||ammonium chloride, ethylene glycol, polyaccrylate|
|Surfactant||Reduction in fluid tension||methanol, isopropanol|
There is currently no requirement for CSG companies in Australia to disclose the constituents in their fracking fluids and only 20 are listed by APPEA as known to be used in Australia.
However, The experience of CSG mining in the USA is that the commercial viability of the CSG industry is dependent on extensive use of stimulation, such as hydraulic fracturing. Indeed, it is estimated that 60-80% of unconventional gas wells drilled in the next decade will require fracking.