About Coal Bed Methane
Is Indonesia Prospective for CBM?
-What is coal bed methane?
-How does coal bed methane form?
-How do you Get the Gas Out of the Coal?
-How Do CBM Wells Produce?
-How Much Gas Can a CBM Well Can Produce?
-What is Permeability and Why is it Important?
-How long can a CBM well produce?
-How is Coal Classified?
-What is the Best Type of Coal For CBM Production?
-How thick should a coal bed be for a viable CBM target?
-Where are the best areas in Indonesia to look for Coal Bed Methane?
-Ingredients for CBM production
What is coal bed methane?
Coal bed methane is natural gas that occurs in coal beds and has been generated during the conversion of plant material to coal (the process known as coalification). Coal bed methane is produced from low rank subbituminous coal.
How does coal bed methane form?
During coalification, accumulated and preserved plant material in ancient swamps and bogs becomes compacted as it is buried. As the material is buried, the pressure expels much of its water content and it converts into peat. With further burial, the temperature of the material increases and thus ever-increasing ranks of coal form, starting with lignite, followed by subbituminous coal and bituminous coal. If the heat (and pressure) is great enough, anthracite (the highest rank of coal) forms. Biogenic methane (generated by bacterial activity) is first to form. When the temperature exceeds that in which bacteria can live, thermogenic methane (that attributed to heating) forms.
How do you Get the Gas Out of the Coal?
Gas is extracted from the coal beds in three ways, 1) free flowing gas from natural fractures, 2) desorption from cleat surfaces (methane molecules detach and enter cleats) and 3) diffusion through coal matrix (methane flowing from high pressure area to low
pressure areas).
How Do CBM Wells Produce?
In general, coal bed methane wells go through three stages during their production cycle. During the dewatering stage, the amount of water produced initially exceeds that of gas, but with continued production, the volume of water continues to decrease as the volume of methane increases.
A stable production stage is reached with maximum methane produced and water production becomes stable.
During the decline stage, the amount of methane produced continues to decline until it becomes uneconomic to continue production.
How Much Gas Can a CBM Well Can Produce?
Well productivity is a measure of the ability of fluid to flow in the reservoir, which in turn is a function of a number of reservoir properties.
Coal bed reservoir properties that control fluid flow are; 1)
Fracture permeability and orientation, 2)
Coal matrix diffusion characteristics, 3)
Desorption isotherm behaviour (gas molecules detaching) 4)
Reservoir pressure
5) Relative permeability 6)
Net coal thickness 7)
Magnitude of stimulation and 7)
Well spacing.
What is Permeability and Why is it Important?
Gas production in coal requires “permeability” in the coal beds.
This is the measure of the ability for gas to flow between the pore spaces in the coal. Coal bed permeability is dependent upon cleat spacing, cleat aperture, and cleat continuity. Cleats are the natural fractures in coal.
How long can a CBM well produce?
The life of a coalbed methane well depends on;
the distance from its neighboring wells (spacing of the well field),
how wells communicate with each other in the subsurface, and
the amount of gas available to each well.
Whilst these factors are not yet that well understood in the license areas held by NuEnergy due to a lack of well
and core data, it is expected that an average well in a producing bed should produce for 10 or more years.
As the gas resident in respective coal beds is extracted, it is common that the same well can be re-worked and completed in other zones either deeper or shallower to produce for many more years. It is thus possible for a single well located in a prolific area to be able to continue producing for 10 to 30 years.
How is Coal Classified?
Coal is classified into;
Grade, which describes the relative percentage of organic to mineral components,
Type which describes the various organic content, (plant constituents) and
Rank, measuring the level of maturation of coal from peat to anthracite.
What is the Best Type of Coal For CBM Production?
Methane generation peaks occur near the boundary between
Medium-Volatile Bituminous and Low-Volatile Bituminous coal stages -
temperature > 100°- 150°Ce .
How Thick Should a Coal Bed be for a Viable CBM target?
The coal thickness required for coal bed methane depends on the gas
content, which is related to the rank and maturation of the coal.
Higher rank coals 3 metres thick have been exploited.
The seams in NuEnergy’s South Sumatra area are up to 30 metres thick located at depths of between 400 and 700 metres.
Where are the best areas in Indonesia to look for Coal Bed Methane?
Map Showing Known Coal Basins in Indonesia - NuEnergy Acreage
interest areas centrally located in Indonesia's coal basins.
|
Ingredients
for CBM production NuEnergy Acerage |
|
| Known, thick, abundant and laterally continuous coal beds | √ |
| Coal-bearing areas with coals of appropriate rank | √ |
| Indications of favourable reservoir for accumulation and preservation of coal bed methane | √ |
| Relatively shallow deposits ~ less than 1,000m | √ |
| Evidence of fracturing and faulting in coal, correct geothermal gradient | √ |
| The presence of gas fields producing from coal-bearing rocks | √ |
NuEnergy's CBM acreage in Indonesia has potential for all of these attributes