Coalbed Methane Compared to Traditional Natural Gas

The primary component of commercial natural gas is methane. Methane can also be found in coal deposits, as it is created by the same biological and geological forces that transform organic material into coal. Methane is stored in coal seams in four different ways:

• as free gas trapped within the pore spaces and natural fractures of
  the coal;
  
• as dissolved gas in the water within the coal seam;
  
• as adsorbed gas on the surface of the coal; and
  
• as adsorbed gas held within the molecular structure of the coal itself.

Methane stored in coal deposits by all four of these methods is released upon the removal of water from coal seams. The removal of water reduces the amount of pressure on free and dissolved gas in the coal allowing it to be produced. As a result, coalbed methane wells typically produce significant amounts of water when they are first drilled, often for the first one or two years of a generally projected eight to twelve year life of these wells. During this de-watering phase, water production typically decreases while gas production typically increases. After this initial production phase, gas production typically declines over the remaining producing life of the wells.

While traditional natural gas wells and coalbed methane wells require largely the same infrastructure and produce the same end product, coalbed methane production differs from traditional natural gas production in the following ways:

• Other than dehydration and compression, coalbed methane typically needs no other processing after extraction prior to entering a pipeline, reducing production costs;
  
• Although certain structural features such as fractures enhance production of coalbed methane, such structural features are generally not necessary for production, making the discovery of coalbed methane reserves less expensive;
  
• Methane bearing coals exist at much shallower depths than the formations that traditionally contain natural gas, allowing coalbed methane to be produced from shallower wells using more readily available equipment, such as water well rigs, thereby reducing drilling costs; and
  
• Since the location of coal seams is typically known through prior mining activity or from data provided by existing wells drilled to deeper formations, extensive geophysical or seismic data is not required to drill a coalbed methane well.

It should be noted that coalbed methane reservoirs require a cleat system to be productive. Cleats are formed during the coalification process and provide the path for the methane to travel to the wellbore. The size and number of the cleats determines the permeability and productubility of the coalbed reservoir.

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