In Situ Gasification (ISG)
ISG occurs when coal is heated underground, in-situ
(being "on site" or "in position") through a highly
controlled process, and transformed from its solid state into a range of
valuable gases, collectively known as synthesis gas, or Syngas.
is produced and extracted through wells drilled into the coal seam, by which
air or oxygen are injected to heat the coal in-situ, and to produce the
synthetic gas (“Syngas”) to the surface for further processing,
transport, or manufacture.
wells that extract the gas are called Production Wells, and Injection Wells
supply the air or oxygen.
Once the Production Well is drilled vertically into the coal seam, it is
cased in steel and concrete to ensure there is no gas leakage.
This well is connected to the gas clean up plant above the ground.
The Injection Well, located some distance away, is drilled
horizontally in the coal seam to precisely intersect the Production Well.
The Injection Well is connected to surface facilities with the oxygen,
air and nitrogen supply equipment.
By creating the right process conditions (pressure, temperature and
oxygen) in the coal seam, a series of chemical reactions occurs, which results
in gasification of the solid coal. The high-pressure natural environment in
deep coal seams (pressure increases with depth) is beneficial to the gasification
process, resulting in more thorough and efficient conversion of coal into
Syngas that is produced to the surface.
Detailed planning is undertaken to locate and
define the parameters of the ISG chamber. The ISG chamber is formed
within the coal itself, with the rock above forming the roof of the ISG
The ISG process starts by heating the coal underground. An Ignition Tool is fed through and to the end of the Injection
Well, to provide heat to start the ISG process and is then
retracted and removed from the ISG chamber.
Oxygen or air is then injected from surface facilities through the
Injection Well into the ISG chamber to commence and then maintain the gasification
process. As the solid coal changes to its gaseous form, a chamber bounded
by coal forms. That is, not all of the coal is gasified. The outer
boundaries of the chamber remain to hold the roof rock above. Controlling
the rate of gasification in the process ensures that the chamber’s integrity is
As the coal is heated a chemical reaction (gasification) occurs inside
the chamber which converts the solid coal into gas. Put simply, the atoms
in the coal, moisture present and oxygen supplied separate under high
temperature and then recombine to form the different gases within Syngas.
Once heat and oxygen are applied to the coal, Syngas is produced.
Importantly, as the ISG process operates in a highly controlled and
constantly monitored environment, it can be stopped quickly and easily at any
time by simply shutting off the oxygen supply.
Due to the differences in pressure in the ISG chamber and the Production
Well, Syngas flows easily from the ISG chamber into the Production Well, and
then to the surface, where it is cleaned and separated for gas distribution
ahead of power generation or fertiliser manufacture.
Advantages of ISG
ISG is not a
new technology or process, and because it has successfully operated in many
demonstration sites and commercial operations in several countries over many
decades, its benefits are well documented. ISG has many advantages,
- Low capital and operating costs
- No surface gasification facilities are needed, hence, capital costs are substantially reduced;
- No coal is transported at the surface, reducing cost, emission control equipment, and costs associated with operating railways, coal shipping and stockpiling;
- The cost of producing ISG gas is lower than surface coal gasification and other non-conventional gas developments.
- Extracting energy from coal too deep or uneconomic to mine.
- Small surface disturbance
- Above ground facilities can be easily located away from sensitive areas without impacting access to targeted coal reserves.
- The need for above ground plant, production, or refinement facilities, or for solid waste handling and disposal operations is eliminated because ash, char, and other solid residual materials from the gasification process remain underground.
- Highly efficient gasification process - small physical footprint for very large amounts of energy extraction and produces energy (gas) efficiently relative to other coal extraction and natural gas production techniques.
- Safe working environment – only small amounts of equipment goes underground, not people and large machines.
- ISG can be conducted at depths well below fresh water, and in saline water.
- ISG eliminates much of the energy waste associated with moving waste rock as well as usable product from the ground to the surface.
- Produces less greenhouse gas than conventional mining.
- Has potential for geologic CO2 storage (known as carbon sequestration).
- ISG delivers significant benefits to regional areas through economic development and the creation of employment opportunities, many of which are long term and include skill advancement roles.