Coal bed methane (CBM) or coal bed gas is a form of natural gas extracted from coal beds. In recent decades it has become an important source of energy. In some areas it is known as coal seam gas. The removal of such methane gas is termed coal bed methane extraction.
The term refers to methane adsorbed into the solid matrix of the coal. It is called “sweet gas” because of its lack of hydrogen sulfide. The presence of this gas is well known from its occurrence in underground coal mining, where it presents a serious safety risk. CBM is distinct from a typical sandstone, carbonate or other conventional gas reservoir, as the methane is stored within the coal by 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 (also called the cleats) may also contain free gas or can be saturated with water.
Since the methane is absorbed into the solid coal matrix, it may be released when the coal seam is depressurized. This often involves drilling a hole into the coal seam and artificially introducing fractures into the seam by hydraulic fracturing techniques similar to those used in recovering hydrocarbons from subterranean formations. Hydraulic fracturing generates long, proppant-supported fractures to release the methane with water in the coal bed. Coal fines (the average particle size is usually less than 50 microns) are carried by methane and water flowing from all directions to the fractures, and then through the fractures to the wellbore for production at the surface. During the methane production, the coal fines will be concentrated at and will plug the flow channels in the near wellbore region, which results in a rapid reduction of production rate.
It would be desirable if methods and/or compositions would be devised to help fix in location or stabilize coal fines in all of its forms and embodiments, particularly those where the coal fines are present in a fluid, such as suspended in air or water. In a particular case, it would be desirable if coal fines within a coal bed in a subterranean formation were treated in such a way that their migration and movement is reduced, inhibited or eliminated.