Coal Seam Gas

Under construction - Michael Aouad

Description:

Coal seam gas or Coalbed methane is a form of natural gas extracted from coal seams. While it is sold and used in the same way as traditional gas it's produced by non-traditional means. Over the last decades it has become an important source of natural gas for the United States and Canada. Australia also has rich deposits of coal seam gas.

It is extracted from the coal and, unlike traditional gas, contains little hydrogen sulfide. Coal seam gas is distinct from a typical conventional gas reservoir, as the gas is stored within the coal by a process called adsorption. The methane is in a near-liquid state, lining the inside of pores within the coal (called the matrix). The open fractures in the coal (called the cleats) can also contain free gas or can be saturated with water - this makes coal both a source and resevoir rock. To extract the gas the pressure in the coal bed needs to be relieved and this id done by pumping out the ground water. The large quantities of extracted water can pose an environmental hazard due to their high sodium content.

Unlike natural gas from conventional reservoirs, coalbed methane contains very little heavier hydrocarbons such as propane or butane, and no natural gas condensate. It often contains up to a few percent carbon dioxide. Coal seam reservoirs usually contain 6 - 7 times more gas than traditional reservoirs.

• [Wikipedia - Coalbed methane]
• [US Geological Survey - Coalbed Methane - An Untapped Energy Resource and an Environmental Concern]
• [Unconventional Gas Center]
• [Energy Justice Network - Coal Bed Methane]

Enablers:

• Availability in nations with little or no traditional gas reserves (e.g. China, India).
• China's demand for coal and extensive coal mines.
• Development and dissemination of reservoir engineering and completion technology (1982 - 1987).
• Growth of natural gas based electricity generation.
• Methane reduction in coal mining leads to less coal mining accidents and lower greenhouse emissions.
• Price and tax incentives (US 1978 - 1980s)
• Regulation on clean energy production.
• Rising awareness of carbon emissions.
• Rising demand for natural gas.
• Risk of nationalisation of traditional sources of natural gas.

Inhibitors:

• Environmental impact of extracting coal seam gas - mainly the disposal of water.
• Movement away from fossil fuels - regardless how clean - towards renewable energy sources.

Paradigms:

• Brings a new view on previously uneconomical coal deposits. Previously if a coal deposit was uneconomical for mining it was left unexploited; now it is possible to extract gas from the coalbed for a much lower cost than mining.
• Changes the way China thinks about meeting energy requirements.
• Coal is now seen as a reservoir rock as well as a source rock.

Web Resources:

• [The Environmental Literacy Council]
• [US Geological Survey]
• [Advanced Technology Group COAL BED METHANE - TECHNOLOGY STATUS]
• [Center for Energy and Global Development - Coal bed Methane: Vision for Clean Energy]