| | CMM | CSG | | |||||||||||||||||||||||||||||||||||||
What is CSG?CSG is generally 95-97 per cent pure methane (CH4). Methane is a colourless, odourless and non-toxic compound that is generally held in the coal seam by pressure, typically provided by water. The amount of gas present in a coal seam depends on the depth of the seam, the thickness and the extent to which the fracture system is interconnected. Why is there a growing interest in CSG?In light of recent LNG proposals Queensland now has the opportunity to establish a LNG sector to capitalise on the global trend towards more environmentally-friendly fuels. Several factors are assisting Queensland in developing a LNG sector including:
How does CSG differ from conventional gas?Chemically, conventional gas and CSG are similar. CSG is almost pure methane conventional gas is around 90 per cent methane with much of the remainder comprising ethane, propane and butane. Conventional gas also often contains higher carbon monoxide levels than CSG. The second difference is geology. Conventional gas reservoirs largely consist of porous sandstone formations capped by impermeable rock, with the gas stored at high pressure and flowing to the surface spontaneously through production wells at a high-flow rate. CSG is entirely infused into the coal and production requires the drilling of many wells with each one less productive than a typical conventional gas well. CSG wells are also typically shallower than conventional wells and cost much less to drill. How is CSG produced?When a CSG well is drilled it is usually hooked up to a pump to remove the water in the coal seam. As water is removed, the pressure reduces and the gas begins to flow at an increasing rate and remains steady for several years. A generalised production profile is illustrated below.
Source: Department of Natural Resources and Water, Facts Mine Series, 2006 At the surface, the CSG is processed with water and other impurities separated. The gas from several wells is then collected and piped to a central compressor station and added to a high pressure pipeline network where it may be mixed with conventional and coal seam gases from different fields and then delivered to users. There is a widespread view that production from CSG wells must be continuous, that is, if production is halted, water will re-enter the seam and the dewatering process must begin again. There are some fields in the Surat Basin that are able to be manipulated with production decreased or stopped for a period with little or no reduction in production, however, this is not a regular situation. Where is CSG found in Queensland?CSG has been produced in the Bowen and Surat basins since 2000. In the period to June 2007, CSG production was about 646PJ1 with 97 per cent coming from the Bowen Basin. However coal seam gas production from the Walloon coal measures in the Surat Basin is now growing rapidly. While proximity to existing infrastructure such as pipelines has been important for exploration, the growing maturity of the sector and demand for gas has seen explorers working in more remote locations. The map below provides the location of gas resources, with the Cooper Basin being a conventional resource and the other basins showing both conventional and coal seam gas resources.
Source: Department of Natural Resources and Water, Facts Mine Series, 2006 What characteristics of coal impacts on CSG production?Coal permeability and the ability of gas to flow within the coal, are significantly affected by water pressure, but the relationship is not uniform. Some coals shrink when drained of water increasing permeability, but others do not and can be self-sealing. The significant variability of coal characteristics even within a single seam, means that many wells are required to adequately map and produce CSG. How much gas is extracted per well?The amount of gas present in a coal seam depends on variables such as the depth and thickness of the seam. Similarly, the amount of gas that is able to be extracted at each well varies between sites. For example, wells in the Fairview field in the Bowen Basin, produce approximately 0.74 terajoules (TJ)2 of gas per day or 270TJ per year. In comparison, wells at fields in the United States such as Cedar Cove in the Black Warrior Basin, produce around 0.11TJ per day (40TJ per year), while wells in the Ignacio Blanco field in the San Juan Basin, USA extract around 1.6TJ per day (580TJ per year). How much water is produced per well?The volume of water extracted with CSG is also highly variable between fields and wells. For instance, production in the Bowen Basin results in the extraction of around 0.063 gigalitres (GL) of water for every PJ of gas, whilst in the Surat Basin around 0.26GL of water is extracted for every PJ of gas. These figures are representative only and actual produced water volumes can vary significantly across individual sites. Further work is proposed to assess production levels. How is gas transported?Over short distances both conventional and CSG gas are transported through pipelines. However this is not practical across long distances. Instead the gas is chilled to -162°C in order to liquefy it. This product is known as liquefied natural gas (LNG) and is about 1/600th of the volume of the gas, meaning it can be shipped economically around the world in specialised cryogenic tankers. These tankers maintain the low gas temperatures necessary to ensure the gas remains in a liquid state. The LNG is then warmed and returned to a gaseous state for use at its destination. What are the main costs of producing and selling CSG?The main costs associated with CSG production include:
What are the environmental impacts?
How does underground coal gasification (UCG) differ from CSG?UCG is a process by which coal is converted in situ to a combustible gas that can be used as a fuel or chemical feedstock. The UCG process involves drilling two boreholes into a deep coal seam and the injection of an oxidant (air or oxygen and/or steam) down one hole. The coal is ignited and gasification is maintained by continuous oxidant flow. The product gas is then recovered from the second hole. While CSG involves the removal of the embedded gas leaving the coal seam intact. Contact the LNG projects team
1 A PJ is a petajoule (or 1015 joules) and is used to express energy consumption by large customers such as cities or major industries, or cumulative output from commercial energy production facilities. As a rule of thumb 55PJ of CSG is required to produce one million tonnes of LNG. 2 A TJ is a terajoule (or 1012 joules) LNG reserves and resources fact sheetThere is significant interest in the development of a liquefied natural gas (LNG) sector in Queensland based on processing coal seam gas (CSG). As the CSG-LNG sector presents both opportunities and challenges, the Queensland Government is conducting a review to help shape its policy response. Where are the CSG reserves located in Queensland?CSG is currently produced in the Bowen and Surat basins, however, CSG can be produced wherever coal exists. In Queensland these locations include the Clarence Moreton, Galilee and Cooper basins.
How are gas reserves measured?There are two measurements of gas reserves that are regularly used:
Gas reserves can be measured in terms of the energy value they contain. The petajoule (PJ) (or 1015 joules) value is the usual unit for the measurement. As a rule of thumb, to produce one million tonnes of LNG, around 55PJ of CSG is required. Another measure is the quantity of gas that can be commercially recovered from known resources. All reserve estimates depend on the reliability of the geological and engineering data available, and the interpretation of this data. Reserve estimates can be adjusted as more data becomes available, and as economic conditions change. There are three measures (see figure 1):
Figure 1 Production reserves are the amount of gas that can be economically recovered. The reserves are classified as follows:
Gas resources are categorised according to the level of certainty about recoverable volumes and then classified according to the potential for the reserve reaching commercial production. Another way of looking at this classification framework is provided in figure 2. An important distinction between resources and reserves is that the recovery of some resources may not be commercially viable. In order to be classified as reserves, commercial barriers to their recovery must have been addressed. If commercial conditions change, quantities of gas may move from one category of reserves to another or may no longer be considered reserves at all. Generally, if gas prices rise, more resources will be converted to reserves. Contingent resources are less certain than reserves. They are potentially recoverable but technological or business hurdles may prevent their commercial development. Prospective resources are estimated volumes of gas associated with unexplored deposits.
For consistency, reserves are mainly quoted in terms of 2P reserves and investment decisions are also based on 2P reserves. Total 2P CSG reserves in Queensland amount to 12 174 PJ. To put this into perspective, on the basis that the Queensland power grid currently utilises approximately 560 PJ/annum, the 2P CSG reserves could provide Queensland with 22 years of power. In terms of the total potential reserves, it is estimated that eastern Australia (Queensland and New South Wales) may have 300 000 PJ of gas in place. How are reserve measures certified?Each company undertakes regular drilling programs with independent certifiers providing updates of the reserve estimates. How quickly are new resources proven?Generally new resources are proven as additional testing is carried out and it becomes more financially attractive to produce CSG and LNG. Contact the LNG projects team
|
|||||||||||||||||||||||||||||||||||||
Search
 |