Coalbed resources hold significant prospects for commercial recovery of

Coalbed methane is one of the most
important unconventional natural gas and a very good source of energy. It is
extracted from the coal beds or coal seams. The formation take place during the
process of coalification and the transformation of plant into the coal. Eventually
it is one of the most important energy resource with reserves and production. CBM
stable source of energy because we can get it by various method. It can be
recovered from underground coal before, during and after mining operations. For
extraction and development of CBM horizontal and vertical wells are used, which
require drilling into the coal seam or coal beds and the water present in the
seam is removed to reduce hydrostatics pressure and released adsorbed gas out
of the coal.

Why
CBM?

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 CBM can fulfil the national goals in India:

Provide a clean burning fuel. Improve
safety of coal mining. Decrease methane vented to the atmosphere that might
cause global warming.  Most importantly
provides a means to use an abundant coal resource that is too deep to mine. It
minimizes the environmental impacts due to coal mining as methane is not lost
to the environment anymore. It is used for other purposes like steel manufacturing,
fuel for industries, fertilizer manufacture, ceramics glass textiles etc.

 

Indian
scenario of CBM

India is a coal rich nation
and has significant volumes of coal bed methane reserves. India has the 3rd
largest proven coal reserves and is the 4th producer in the world. In India,
CBM is being produced from the Gondwana coalfields of Raniganj, Jharia and
Sohagpur. Total coal resources of India are approximately 300B. The mining
industry is over two centuries old. The prognosticated CBM resources are around
4.6TCM. Moreover, the estimated CBM resources hold significant prospects for
commercial recovery of natural gas. Deeper reserves from which recovery of CMB
seems less feasible, technologically as well as economically, may be the prime
targets for enhanced recovery techniques, for example the coal seams which are
found at greater depths and are below the limit of mining are considered
suitable for these techniques. India stepped into CBM exploration and
production decades after the US success. Methane is native to coal and forms
during the coalification process. It has traditionally been recognized as an
evil companion of coal bringing in major safety problems in underground mining
until recently when it changed from a mining hazard to an effective energy
resource. In recent times CBM is receiving increased attention as a valuable
fuel source.

Coal is the source as well as
reservoir to significant quantities of methane, a potentially economic
resource. The huge reserves of coal in India may be categorized in two types,
based on their period of formation namely Gondwana coal and Tertiary coal.
Nearly 99% of the total coal reserves in India belong to Gondwana basins and
are characteristically different from the rest of the tertiary coal. The major
focus of research and development in CBM sector has been based mainly on
Gondwana coals.

PROBLEMS
ASSOCIATED IN CBM WELLS

Drilling operation:

Underbalanced
Drilling (UBD) is a technique in which oil, gas or geothermal wells are drilled
using pressures lower than the reservoir pressure. The result is an increase in
rate of penetration (ROP), reduced formation damage and reduced drilling costs.
Air drilling provides an efficient system in terms of operations costs and
environmental safety benefits.

Two major problems occur at the time air drilling i.e. caving of the
well and the waterinflux comes into the wellbore from the formation because

Ø  Formation pressure
control is minimal and, therefore, drilling is limited to geological regions
where reservoir pore pressures are low.

 

Ø  There is little or no
fluid pressure to support the borehole wall and prevent sloughing.

 

Ø  There is limited
ability to cope with significant volumes of water entering the annulus from
water producing formations.

 

In most of the wells (about 80%) air drilling method is not successful
and we switch to the mud drilling.

In few of the wells the shale section could not be air drilled and in
such cased drilling was carried out by KCl (shale inhibitor), PHPA (polymer)
mixed in the mud and the top section completed. The coal seams have been
drilled with air/mist to avoid any formation damage.

Progressive cavity pump:

The Progressive Cavity
Pump (PCP) was invented by Rene Moineau in 1932. PCP’s became widely used as
surface pumps, especially for the pumping of viscous mixtures. The PCP is able
to produce highly viscous sand layden fluids, making it the primary artificial
lift system for conventional heavy oil production around the world. KUDU along
with PCM, have led the development of high capacity, high head lift pumps as
well as elastomers that are resistant to medium and light crudes. PCP’s are
also utilized for dewatering coal bed methane and conventional gas wells.