Page 125 - DGH_Annual_Report

Unconventional Petroleum Resources 125

b. Coal Mine Methane (CMM) - Methane gas hydraulic fracturing (fracking). These techniques
captured at working mine by underground open up more reservoirs contact and create
methane drainage techniques. Any gas sufficient fracture conductivity to release the
captured underground, whether drained trapped gas and oil.
in advance or after mining, and any gas
drained from the surface of well is including 7.1.3 Tight Gas:
in this definition. Tight gas refers to natural gas trapped in

c. Ventilation air methane (VAM) - Methane low-permeability rocks other than shales, viz.
emitted from coal seams that enters the sandstones, siltstones or carbonates. Like shale
ventilation air and are exhausted from the gas, tight gas extraction requires hydraulic
ventilation shaft at a low concentration, fracturing to create flow conduits. Tight gas is
typically in the range of 0.1% to 1.0% by genetically conventional deposits, however due
volume. to location in the deeper part of the basins, it
loses intra granular porosity due to excessive
d. Abandoned Mine Methane (AMM) - The over-burden pressure. For the same reasons,
methane gas recovered from abandoned such deposits are often developed into high
coal mines. pressure and high temperature conditions
making gas extraction more challenging.
7.1.2 Shale Gas and Shale Oil:
7.1.4 Gas Hydrates:
Gas or oil within shales are the un-expelled part
during petroleum generation process and found Gas hydrates are crystalline ice-like structures
trapped within the pore space of shale as the that contain methane and other gases. They
source rock. Genetically, shales have no intrinsic are found in deep ocean several hundred meter
permeability for self-flow to a well bore. below seabed and also in permafrost regions. It
is formed under moderately high pressure but
Like all other unconventional resources of low temperature conditions.
continuous nature, shale plays too have less
geological risks than conventional but more Extraction is still experimental, involving methods
development risks. like depressurization, thermal stimulation, and
inhibitor injection to dissociate the hydrate. Gas
Shale gas and oil have significantly increased hydrates hold vast amount of natural gas as
global energy supplies and have transformed 1-unit hydrate volume expands into ~160-unit
the energy landscape in countries like the USA. gas to surface and represent a potential future
The commercial extraction of shale gas and oil energy source.
involves the use of horizontal drilling followed by