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The Guide To Unconventional Hydrocarbons - Part 1 - Coal Bed Methane

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Posted: 07/05/2011
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Coal bed methane (CBM), otherwise known as coal seam gas (CSG) has become one of the most important energy sources of the last few decades. Simply put, it is methane found in underground coal seams.

CBM is generated either from a biological process as a result of microbial action or from a thermal process as a result of increasing heat with depth of the coal.

Often a coal seam is saturated with water and the methane is held in the coal by water pressure. Natural gas from coalbeds accounts for approximately 7 per cent of the total natural gas production in the United States.

Extraction

Since coal bed methane travels with ground water in coal seams, extraction of CBM involves using pumps to dewater the seam in order to depressurize it, which allows the methane to break free from the coal. As the amount of water in the coal decreases, gas production increases.

CBM has very low solubility in water and readily separates as pressure decreases, allowing it to be piped out of the well separately from the water. Water moving from the coal seam to the well bore encourages gas migration toward the well.

Exploration expenditure for coal bed methane is relatively low in mining terms, and the wells are cost-effective to drill as they are not excessively deep, making CBM a great option for countries where technological capabilities are not so advanced.

Residual water from the dewatering process is usually stored in pools and evaporated off.

Growth Areas

As the world's largest coal producing nation, China is aiming for CBM to fulfil 14 per cent of its domestic gas needs by 2030, outputting 12 billion cubic feet every day.

In the USA, there is an estimated 100 trillion cubic feet of coal bed methane readily exploitable with today's technologies, and a further 600 trillion cubic feet for the taking.

Indonesia, the world's largest coal exporter, has one of the largest coal bed methane reserves in the world, estimated at approximately 453 trillion cubic feet dotted about its vast archipelago

Canada boasts 260 trillion cubic feet of CBM, mostly in the western province of Alberta where the country's only expressly-built coal bed methane wells sit on top of 170 trillion cubic feet of exploitable methane.

In Queensland, Australia, the Surat and Bowen Basins hold an estimated 250 trillion cubic metres of CBM and the central Port of Gladstone is currently undergoing a £2.3 billion expansion to accommodate expected demands.

Potential

Exploration expenditure for coal bed methane is relatively low in mining terms, and the wells are cost-effective to drill as they are not excessively deep, making CBM a great option for countries where technological capabilities are not so advanced.

There is also the possibility that, unlike the coal that lines the seams it is extracted from, coal bed methane gas is, in fact, a renewable resource as the microbiological reaction that forms the methane is ongoing as long as the right conditions are maintained.

Add to that the fact that CBM is a relatively clean fuel too, emitting around half the CO2 of black coal when used to produce electricity and almost 70 per cent less than brown coal.

Concerns

The main concerns of CBM exploitation come from possible environmental impacts. The residual water produced as a result of coal seam dewatering is highly saline in content and could possibly be deleterious to the soil quality and vegetation in the immediate environs of a CBM project.

An example of this can be seen at the Chinchilla CBM development, 290 kilometres west of Brisbane in Queensland, Australia. High salinity has led to large scale degradation of the contiguous land and necessitated the building of a specialised water treatment plant to mitigate further problems.

Verdict

If environmental concerns are properly dealt with, there is no reason why coal bed methane gas - as a bountiful and renewable resource that is relatively cheap to exploit - could not be an empowering energy source for developed and developing countries for hundreds of years.

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