Shale Gas and Coal-bed Methane Fossil fuels (such as gas, oil and coal), are produced by the slow decomposition of organic matter buried underground as a result of increased temperature and pressure. Shale gas and CBM differ from conventional gas reservoirs as the gas is directly extracted from the rock that was the source of the gas (shale and coal respectively).
Shale Gas:
Shale gas refers to natural gas that is trapped within fractures and pore spaces within fine-grained sedimentary shale rocks. The Tyndall Centre (2011) identified two major drilling techniques that are used in combination with one another to extract shale gas – horizontal drilling and hydraulic fracturing:
▼Horizontal drilling is used to provide greater access to the gas trapped deep in the producing formation. At the desired depth, the drill bit is turned to bore a well that stretches through the reservoir horizontally, exposing the well to more of the producing shale;
▼Hydraulic fracturing is where fluid (water, sand and other substances) are pumped into the well at pressure to create and increase fractures in the rock. These fractures start at the injection well and can extend a few hundred metres into the reservoir rock. A material such as sand holds the fractures open, allowing hydrocarbons to flow into the reservoir rock. Between 15 and 80 per cent of the injected fluids are recovered to the surface3. Fluid that returns to the surface is captured, treated and disposed of and gas that flows to the surface is captured and used for electricity generation or is put into the mains supply. It is also possible to „frack‟ a well several times in its lifetime to increase yield.
Shale gas in India:
Cambay, Krishna-Godavari, Cauvery, Damodar Valley, Upper Assam, Pranhita-Godawari, Rajasthan and Vindhyan basins
Shale Gas:
Shale gas refers to natural gas that is trapped within fractures and pore spaces within fine-grained sedimentary shale rocks. The Tyndall Centre (2011) identified two major drilling techniques that are used in combination with one another to extract shale gas – horizontal drilling and hydraulic fracturing:
▼Horizontal drilling is used to provide greater access to the gas trapped deep in the producing formation. At the desired depth, the drill bit is turned to bore a well that stretches through the reservoir horizontally, exposing the well to more of the producing shale;
▼Hydraulic fracturing is where fluid (water, sand and other substances) are pumped into the well at pressure to create and increase fractures in the rock. These fractures start at the injection well and can extend a few hundred metres into the reservoir rock. A material such as sand holds the fractures open, allowing hydrocarbons to flow into the reservoir rock. Between 15 and 80 per cent of the injected fluids are recovered to the surface3. Fluid that returns to the surface is captured, treated and disposed of and gas that flows to the surface is captured and used for electricity generation or is put into the mains supply. It is also possible to „frack‟ a well several times in its lifetime to increase yield.
Shale gas in India:
Cambay, Krishna-Godavari, Cauvery, Damodar Valley, Upper Assam, Pranhita-Godawari, Rajasthan and Vindhyan basins
Coal-bed Methane
Coal-bed Methane CBM is different to other traditional gas reservoirs as methane is held within the coal by adsorption. CBM is defined as gas extracted from intact coal seams, in contrast to gas extracted from active or abandoned mines. Extraction of CBM involves drilling down into coal seams, pumping out the groundwater, and the resultant drop in pressure is sufficient for methane held within the coal to be released. Boreholes can also be extended laterally along coal seams to increase extraction volumes. The methane is pumped up to the surface and either burnt for electricity or pumped to the national grid. Occasionally, CBM extraction may need to be enhanced by hydraulic fracturing due to insufficient natural permeability within the coal.
Coal-bed Methane in India:
Coal mines
Coal-bed Methane CBM is different to other traditional gas reservoirs as methane is held within the coal by adsorption. CBM is defined as gas extracted from intact coal seams, in contrast to gas extracted from active or abandoned mines. Extraction of CBM involves drilling down into coal seams, pumping out the groundwater, and the resultant drop in pressure is sufficient for methane held within the coal to be released. Boreholes can also be extended laterally along coal seams to increase extraction volumes. The methane is pumped up to the surface and either burnt for electricity or pumped to the national grid. Occasionally, CBM extraction may need to be enhanced by hydraulic fracturing due to insufficient natural permeability within the coal.
Coal-bed Methane in India:
Coal mines
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