Model Answer
0 min readIntroduction
Coal Bed Methane (CBM) is an increasingly important unconventional natural gas resource. It refers to methane gas trapped within coal seams. While natural gas is primarily found in porous sandstone reservoirs, CBM is adsorbed onto the surface of the coal matrix. The growing global energy demand and advancements in extraction technologies have led to increased interest in CBM as a viable energy source. India, with its vast coal reserves, holds significant potential for CBM exploitation, aiming to reduce its reliance on imported natural gas and enhance energy security.
What is Coal Bed Methane?
CBM is primarily methane (CH4), but can also contain varying amounts of nitrogen, carbon dioxide, and other gases. Unlike conventional natural gas, CBM is held within the coal matrix through adsorption – a process where gas molecules adhere to the surface of the coal. The amount of methane adsorbed depends on factors like coal rank (degree of metamorphism), coal pressure, temperature, and the surface area of the coal. Higher rank coals (anthracite) generally have lower methane content compared to lower rank coals (bituminous, sub-bituminous, lignite).
Formation of Coal Bed Methane
CBM is biogenic in origin, meaning it is produced by the microbial decomposition of organic matter during the coalification process. This process occurs over millions of years as plant matter accumulates in swampy environments and is gradually transformed into peat, then lignite, bituminous coal, and finally anthracite. Microorganisms break down the organic matter, releasing methane as a byproduct. The methane is then trapped within the coal’s porous structure.
How is CBM Exploited?
Exploiting CBM requires removing water pressure from the coal seam, which allows the adsorbed methane to desorb and flow to a wellbore. The process typically involves the following steps:
- Well Drilling: Vertical or directional wells are drilled into the coal seam.
- Water Pumping: A significant amount of water is present within the coal seam. This water is pumped out, reducing the hydrostatic pressure. This is the most crucial step.
- Gas Flow: As water pressure decreases, methane desorbs from the coal and flows along with the water to the wellbore.
- Gas Processing: The produced gas stream (methane, water, and other gases) is sent to a processing facility where water and impurities are removed, and the methane is prepared for pipeline transmission.
Exploitation Techniques
Several techniques are used for CBM exploitation:
- Conventional CBM: This involves drilling vertical wells and pumping water. It’s suitable for relatively shallow, permeable coal seams.
- Horizontal Drilling: Horizontal wells are drilled within the coal seam, increasing the contact area and enhancing gas flow. This is particularly effective for thicker coal seams.
- Multi-Lateral Drilling: Multiple horizontal wells are branched from a single vertical wellbore, further maximizing the contact area.
- Hydraulic Fracturing (Fracking): In low-permeability coal seams, hydraulic fracturing is used to create fractures in the coal, enhancing gas flow. This involves injecting high-pressure fluid into the wellbore. However, fracking raises environmental concerns.
CBM Exploitation in India
India has significant CBM resources, estimated at over 90 trillion cubic feet (TCF). Key CBM blocks are located in the Damodar Valley (Jharkhand, West Bengal), the Godavari Valley (Andhra Pradesh, Telangana), and the Raniganj Coalfield (West Bengal). Reliance Industries Limited (RIL) operates the Raniganj South CBM block, which is one of the earliest and most successful CBM projects in India. The government has implemented policies to encourage CBM exploration and production, including the CBM policy in 1997 and subsequent amendments.
| Coalfield | State(s) | Estimated CBM Reserves (TCF) |
|---|---|---|
| Damodar Valley | Jharkhand, West Bengal | ~60 |
| Godavari Valley | Andhra Pradesh, Telangana | ~20 |
| Raniganj Coalfield | West Bengal | ~10 |
Environmental Concerns
CBM exploitation can have several environmental impacts:
- Water Management: Large volumes of water are produced during CBM extraction, which can be saline and contain trace elements. Proper disposal or treatment of this water is crucial.
- Groundwater Contamination: Leakage from wells or improper disposal of produced water can contaminate groundwater resources.
- Methane Emissions: Methane is a potent greenhouse gas. Leakage during production and processing can contribute to climate change.
- Land Subsidence: Large-scale water withdrawal can potentially lead to land subsidence.
Conclusion
Coal Bed Methane represents a significant unconventional energy resource with the potential to contribute to India’s energy security. While exploitation technologies are becoming increasingly sophisticated, careful consideration must be given to the environmental impacts associated with CBM extraction. Effective water management, stringent well integrity standards, and monitoring of methane emissions are essential for sustainable CBM development. Further research and development into cleaner extraction technologies are also crucial for maximizing the benefits of this resource while minimizing its environmental footprint.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.