I am compiling this article as the union cabinet has given clearance to Coal India Limited for CBM explorations (Hindu 20/12/13).
Here I have given details of CBM as energy resource its importance, extraction process, deposits in India and world.
Also a Q&A format is provided in the end for brief details.
Brief:
1. The existing rules prohibit mining firms from extracting CBM during mining as the policy does not allow for simultaneous extraction of CBM and coal. CBM exploration and production is allowed only in pure coal-seam gas bearing blocks, which are auctioned. Since 2001, 33 CBM blocks have been awarded in four auction rounds. According to the Directorate General of Hydrocarbons (DGH), India has CBM reserves of about 4.6 trillion cubic meters.
2. CIL holds at least 20% of the estimated 60 billion tons of coal resources in India. It has coal mines in eight States, which are estimated to have CBM reserves of 3.5-4 trillion cubic feet. It was felt that many of the acreage of CIL were gaseous and unsafe mines, where mining of coal would be possible only after the extraction of CBM.
COAL BASED METHANE (CBM)
Introduction
Coal bed methane extraction is one of the nation's fastest growing alternative energy industries, currently accounting for approximately seven percent of the nation's natural gas supply. Coal bed methane extraction is a process for collecting methane reserves from coal deposits. The increasing demand for alternative energy sources and cleaner burning fossil fuels will undoubtedly continue to stimulate growth in this emerging industry. Although coal bed methane is touted as "clean" energy; the extraction of coal bed methane has significant environmental consequences on the local ecology. At particular risk are local residents, farmers and businesses relying on ground and surface water for domestic purposes.
To meet the rapidly increasing demand for energy and faster depletion of conventional energy resources, India with other countries is madly searching for alternate resources like coal bed methane (CBM), shale gas, gas hydrate. CBM is considered to be the most viable resource of these
Coalbed methane is generated during coalification process which gets adsorbed on coal at higher pressure.
However, it is a mining hazard. Presence of CBM in underground mine not only makes mining works difficult and risky, but also makes it costly. Even, its ventilation to atmosphere adds greenhouse gas causing global warming. However, CBM is a remarkably clean fuel if utilizedefficiently. CBM is a clean gas having heating value of approximately 8500 KCal/kg compared to 9000 KCal/kg of natural gas.
It is of pipe line quality; hence can be fed directly to national pipeline grid without much treatment. Production of methane gas from coalbed would lead to de-methanation of coalbeds and avoidance of methane emissions into the atmosphere, thus turning an environmental hazard into a clean energy resource.
INDIA
As the third largest coal producer in the world, India has good prospects for commercial production of coal bed methane. Methane may be a possible alternative to compressed natural gas (CNG) and its use as automotive fuel will certainly help reducing pollution levels. India is one of the select countries which have undertaken steps through a transparent policy to harness domestic CBM resources. The Government of India has received overwhelming responses from prospective producers with several big players starting operations on exploration and development of CBM in India and set to become the fourth after US, Australia and China in terms of exploration and production of coal bed methane. However, in order to fully develop India's CBM potential, delineation of prospective CBM blocks is necessary. There are other measures like provision of technical training, promotion of research and development, and transfer of CBM development technologies that can further the growth of the sector. India lacks in CBM related services which delayed the scheduled production. Efficient production of CBM is becoming a real challenge to the E & P companies due to lack in detailed reservoir characterization. So far, the most investigations have been limited to measurement of adsorption isotherms under static conditions and is deficient in providing information of gas pressure-driven and concentration-driven conditions. More care should be taken on measurement of porosity and permeability also. To produce more methane from the coal enhanced technology like CO2 sequestration may be implemented. This process can not only reduce the emission of this gas to atmosphere, will also help in extra production of methane gas. Though, presently, CO2 is not an implemented much because of high cost. But the necessity to reduce greenhouse gas emissions has provided a dual role for coalbeds - as a source of natural gas and as a repository for CO2. In the present investigation, Singareni coal field has been selected as the study area. Samples have been collected from various locations & depths. Standard methods have been followed to characterize the collected coal samples and evaluation gas reserve.
Global
The largest CBM resource bases lie in the former Soviet Union, Canada, China, Australia and the United States. However, much of the worlds CBM recovery potential remains untapped. In 2006 it was estimated that of global resources totaling 143 trillion cubic meters, only 1 trillion cubic meters was actually recovered from reserves. This is due to a lack of incentive in some countries to fully exploit the resource base, particularly in parts of the former
Soviet Union where conventional natural gas is abundant.
PRODUCTION
Production of gas is controlled by a three step process (i) desorption of gas from the coal matrix, (ii) diffusion to the cleat system, and (iii)flow through fractures
Many coal reservoirs are water saturated, and water provides the reservoir pressure that holds gas in the adsorbed state. Flow of coal bed methane involves movement of methane molecules along a pressure gradient. The diffusion through the matrix pore structure, and steps include desorption from the microspores, finally fluid flows (Darcy) through the coal fracture (cleat) system. Coalseams have two sets of mode; breaking in tension joints or fractures that run perpendicular to one another. The main hurdle associated with the production of CBM is the requirement of long dewatering of coal bed before production. This difficulty may be resolved to some extent with implementing the CO2 sequestration technology. Due to higher adsorption affinity of CO2 to coal surface, methane will be forced to desorbs from the coal surface at comparatively high pressure and can reduce the dewatering time and hence the total project period. Also the problem associated with variation in coal properties related to pressure depletion may be alleviated. China, Australia, USA have been started to implement this technology for enhanced recovery of CBM gases.
CONCLUSIONS
CBM technology is proceeding with good space to prove itself as a cleaner energy security to India as well as the World. However, production strategy of methane from CBM is very much different from conventional gas reservoir. The study revealed that the coal type, rank, volatile matter and fixed carbon are strongly influence the adsorption capacity of methane into the coal bed. With increasing depth maturation of coal increases and generation of methane gas also increases. Gondwana basin as the most prospective CBM field is being developed now. From the studies, it is observed that Singareni coal field under Gondwana basin contains low gas. Hence, presently it is not considered for CBM extraction. However, in future this field may be considered for methane extraction using advanced technology and in emergency condition
http://www.ijcea.org/papers/113-A618.pdf
Q &A Format
What Is Coal Bed Methane?
Coal bed methane is a natural gas by-product of coal formation. During coal formation, organic matter is chemically broken down into simple organic compounds. Methane is a by-product of this breakdown.
Coal is very porous but lacks matrix permeability. In other words, water can seep into coal but can't flow through it. Naturally occurring fractures in coal allow ground water to permeate the coal and provide the means through which the methane is stored in the coal bed. Due to coal's porous nature, methane gas produced during coal formation is absorbed into the coal bed and held in place by the weight of the surrounding groundwater.
How Is Coal Bed Methane Extracted?
In order to commercially produce coal bed methane, it is necessary to decrease the water pressure within the coal bed. When the pressure is decreased, the methane gas naturally desorbs from the coal and migrates through the coal bed.
This natural phenomenon is the basis for coal bed methane production. In extracting methane from coal beds, a well is drilled down to the coal bed and the sides of the well are then encased in concrete. A water pump is dropped down into the coal bed and the top of the well is sealed with a venting pipe to collect the methane. Large amounts of groundwater are pumped out of the coal bed, causing a corresponding decrease in water pressure. The decreased water pressure allows the methane to escape from the coal and migrate along the coal fractures and up into the well. The methane is then pumped from the well through the venting pipe where it is compressed and sold.
What Are the Environmental Effects of Coal Bed Methane Extraction?
Water Depletion.
One of the environmental effects of coal bed methane extraction is the immense quantity of water pumped out of the coal bed aquifers. On average, approximately 12-15 gallons of water per minute are pumped from each well. During the initial phase of production, water is pumped at a very high rate. The extracted water is typically discharged into local streams or reinjected into the ground. Where the coal bed groundwater is relatively pure, surface discharge is the most common method of disposal. Smaller quantities are sometime stored in large pits for evaporation but this method is inefficient to deal with massive quantities of extracted groundwater. The removal and disposal of so much groundwater raises several concerns.
One concern is that drainage of a coal bed aquifer will cause shallower aquifers to drain into the cavity created by the coal bed water extraction. This is a particular concern for local landowners relying on well water pumped from shallow aquifers, which is often the case, as aquifers used for domestic water wells tend to be shallower than coal bed aquifers. In several reported cases, local water wells have gone dry after coal bed methane operations have begun.
A similar concern exists for coal bed aquifers that are tributaries to surface waters or adjacent groundwater aquifers, i.e., coal bed aquifers that contribute to other water sources. The drainage of tributary coal bed aquifers can cause a corresponding decline in the water levels of the contributory water sources. Consequently, water depletion from coal bed methane operations can have a significant impact on residents, farmers and businesses relying on affected water supplies.
Surface Water Discharge.
Because surface discharge is the most common disposal option for the extracted coal bed water,
the compositional characteristics of coal bed water can have a tremendous impact on the surrounding ecology. The quality of coal bed water varies considerably from well to well and basin to basin, but, on average, the deeper the coal bed, the more saline the water becomes. Other compositional elements typically seen in extracted coal bed water include:
Major Cations (positively charged ions such as sodium, potassium, magnesium, & calcium)
Major Anions (negatively charged ions such as chlorine, sulfate, & hydrogen carbonate)
Trace Elements & Metals (iron, manganese, barium, chromium, arsenic, selenium, & mercury)
Organics (hydrocarbons and additives).
The saline and sodic quality of coal bed water can have catastrophic impacts on local agriculture when discharged into local waterways. The moderate to high levels of salt in coal bed water can destroy soils and decrease crop production. The salts gather in the root base of plants, making it harder for the plants to extract water from the soil and inhibiting growth. As many farmers make use of stream and river diversion to water their crops and grazing fields, the surface discharge of coal bed water can negatively impact local agriculture.
Unlike salinity, which measures the quantity of dissolved salts in water, sodic water is measured by the proportion of sodium to calcium and magnesium. Sodic water interacts with fine soils, like clay, and results in the formation of a hard crust that severely impairs water and air permeation. Sodic water can cause a sharp decrease in the growth of crops and other vegetation.
Chemical & Radioactive Contamination.
Because coal bed methane extraction depends upon the natural fractures within the coal bed, gas companies routinely attempt to increase the extent of coal bed fracturing in order to boost methane production. Hydraulic fracturing is a technique used for this purpose. Hydraulic fracturing pumps a mixture of heavy chemicals, water, sand and/or other materials down an extraction well under extremely high pressure in order to achieve the desired fracturing. Hydraulic fracturing raises serious concerns because of the chemicals being used and their impact on the local ecology.
If the coal bed aquifer is tributary to surface water or other groundwater aquifers, chemical contamination can spread into domestic, agricultural, and industrial water supplies. Because hydraulic fracturing typically precedes the water extraction phase, much of the fracturing fluid will be pumped out of the aquifer along with the bulk of the groundwater. Where surface discharge is used to dispose of the extracted groundwater, the fracturing fluid is discharged along with the groundwater directly into local waterways, potentially contaminating water sources relied upon by local communities.
The types of chemicals used in fracturing fluids vary from company to company. In some states, companies are not required to disclose the chemicals used in their mining operations, so the extent of contamination is still unknown. Based on Material Safety Data Sheets obtained from several coal bed methane operators, many of the chemicals used are highly toxic, water soluble, volatile, and highly mobile-some are even radioactive.
Despite the fact that large amounts of hazardous chemicals are known to be injected directly into the coal bed aquifer, there is shockingly little oversight. Coal bed aquifers often contain potable or high-quality water and the injection of fracturing fluids into such water sources can permanently contaminate a viable source of water.
Conclusion
Coal bed methane production is a rapidly growing industry that will undoubted continue to expand under the nation's demand for alternative energy sources. Although global climate concerns have illustrated the need for the development of clean burning fossil fuels, coal bed methane production is not without its environmental hazards. Water depletion from coal bed methane production can adversely impact adjacent residents, farmers and businesses that rely on local groundwater and surface waters. The saline and sodic quality of coal bed water can inhibit plant growth when discharged into local waterways. Chemical contamination resulting from hydraulic fracturing poses a significant threat to domestic, agricultural, and industrial water supplies and anyone unfortunate enough to be exposed to such hazardous materials. While the use of cleaner energy sources must be encouraged, such development should not proceed to the detriment of local communities.
by Rahul Khairnar
References
http://www.brianmcmahonlaw.com/CM/Client-Bulletin/Client-Bulletin7.html
http://www.ijcea.org/papers/113-A618.pdf
