Coal Bed Methane
|
|
Coal Bed Methane (CBM) is a form of natural gas, composed mostly of methane, which is found in coal beds worldwide. It is often referred to as unconventional because it is stored within the matrix of the coal itself instead of within the pores of the host rock. As lush vegetation in ancient swamps accumulated and was buried under tons of sediment over millions of years, methane gas was produced and trapped in the newly formed coal beds and held there by a process known as adsorption. Adsorption involves the Coal Bed Methane becoming trapped within the matrix of the coal. It is held in place by the enormous pressure of the rock and sediment above the coal seam and will become liberated if that pressure is reduced either naturally or through drilling. Miners have known about the presence of Coal Bed Methane in coal mines for centuries, however in the past it was viewed as an explosive danger in mines and was something to be avoided or controlled. Times have changed. Coal is now recognized as a “reservoir rock” with enormous potential for a secondary energy resource, and Coal Bed Methane is considered as the next clean energy resource for the industrialized world. Most countries with measurable coal reserves will have Coal Bed Methane reserves as well and in many cases those numbers are very large. A 1997 US Geological Report estimated that there could be as much as 100 trillion cubic feet (tcf) of economically recoverable Coal Bed Methane in the US and 260 tcf in Canada. With continued high energy prices and dwindling conventional reserves, the exploration for and production of Coal Bed Methane is likely to continue to increase in the future. Factors Affecting Production The production of Coal Bed Methane requires drilling either vertically or horizontally into the coal seam. Several factors will determine how much Coal Bed Methane the coal seam is likely to contain and how easily it will transport through the coal into the well. The adsorption capacity of coal is a measure of its capacity to contain Coal Bed Methane within its matrix and depends strongly on the quality and rank of the coal. More importantly from a production point of view is the permeability of the coal seam. Coal’s permeability depends almost entirely on fractures or cleats within the seam, either butt cleats or face cleats. These run at right angles to each other, with the face cleats being more continuous and the butt cleats ending at the face cleats. A higher density of continuous cleats will result in a higher intrinsic permeability of the coal, which generally results in a more productive Coal Bed Methane well. Coal Bed Methane wells is typically drilled 100 – 1500 m deep to intercept the coal seam of interest. Pressure within the coal seam then has to be reduced for the Coal Bed Methane to begin desorbing from the coal matrix and start flowing through the fractures into the well. Coals that are water saturated will require some water be pumped out to reduce the pressure within the coal seam. Seams that are gas saturated will produce Coal Bed Methane with very little water production. Unlike conventional gas wells, which almost always produce varying quantities of saline water, Coal Bed Methane wells can produce either none or some water, which can be saline or fresh. Generally the resulting methane gas produced from Coal Bed Methane wells is almost pure methane containing very little hydrogen sulfide or other impurities and can be fed directly into existing natural gas pipelines. Environmental Concerns Environmental Coal Bed Methane production is similar to that of conventional gas. An increased number of wellheads and pipelines can detract from the natural beauty of an area and increase the fragmentation of the local environment. Water produced from Coal Bed Methane wells can be quite saline and contain environmentally damaging substances such as sodium. In addition, continuous pumping from Coal Bed Methane wells can draw down potable water tables and diminish local reservoirs. Proper measures need to be taken to ensure companies are in compliance with local water and environmental regulations. Flaring or venting of gases is generally more common for the first few wells in an area but is generally less of a concern with additional wells because of the intrinsically low pressures associated with Coal Bed Methane production. This low pressure requires most Coal Bed Methane wells to undergo compression during a large portion of their production life and the noise associated with these processes needs to be monitored and controlled to adhere to local noise regulations. In summary, environmental concerns with Coal Bed Methane drilling and production are quite similar to those for conventional gas, and existing environmental regulations will be sufficient to address most concerns. Equipments To enable us to test the CBM & CMM, SGS has procured the equipments like controlled temperature Gas Desorption Canister for the Gas desorbed test in coal core samples from the drilling site. Motorized coal crushing rod mill for Lost gas measurement (Desorbed gas, residue gas and Lost gas) and Portable Gas volume measurement Systems .The method as per the SOP is known as Direct Method for estimation of INSITU Gas content in coal . Two units Gas chromatographs (Perkin –Elmer Arnel engineered) to determine the gas composition, are installed and calibrated by using standard gas successfully as per ASTM-D-1946. Metallic canisters designed and fabricated locally for collection of CBM Gas from the bore holes, Gas sampling tubes made of glass, Aspirator bottles and Gas Storing tubes have been designed and fabricated locally. Method Validation Gas chromatograph has been calibrated by the supplier by using standard gas mixture. Please find the below table -1, which provides the Standard gas values obtained after the calibration of the Gas Chromatograph. The values obtained and Standard values are with in the repeatability limit. Table - 1
As for the validation of method for desorption test SGS India will test the same core coal sample, for desorption test IN SITU gas content analysis as per the Method attached at its facility as well as at CMRI Dhanbad. After comparing the results of Analysis obtained at both institutes the required approvals for the Method validation will be sort. Experts SGS has on it consultant roles Dr.T.K.Goswami, Retired Deputy director from CFRI (Central Fuel Research Institute), having more than 40 years of experience in fuel research institute and rich experience in Gas Chromatography, he was the head of the Chromatography Division. And Dr. B.D.Banarjee ,Retired Head for Coal Bed Methane testing, from CMRI, having more than 35 years experience, the only Institute in India executing the CBM Analysis Projects, he was the scientist who has developed the methods for CBM analysis . Service offer to customer With the above in place SGS is now capable to offer the following service matrix to its customers:
|
