Generic abandoned mines
[edit / update model]Summary
This methodology represents methane (CH4) emissions associated with abandoned, underground coal mines. The data and calculation methodology are sourced from the IPCC, as published in Volume 2, Chapter 4 - Fugitive Emissions of their 2006 IPCC Guidelines for National Greenhouse Gas Inventories.
The methodology
Emissions model
After closure, coal mines may continue to emit methane as a result of in situ gases migrating through natural or manmade conduits such as old portals, vent pipes, or cracks and fissures in the overlying strata. Abandoned mines may flood as a result of groundwater intrusion or surface flow, in which case emissions from completely flooded abandoned mines can be treated as negligible. Non-flooded or partially-flooded mines can continue to produce methane (CH4) emissions over a long period of time.
This methodology calculates the annual fugitive CH4 emissions from abandoned mines, and is specifically applicable to mines considered to be 'gassy' during the period in which they were active. The methodology represents the IPCC tier 1 approach.
Emissions are calculated on the basis of generic emissions factors which describe the typical annual quantity of CH4 emitted by a single mine. Multiplying these emissions factors by the number of mines under consideration provides an estimate of total annual CH4 emissions.
Also factored in to calculations is the quantity of CH4 which is recovered during the annual period under consideration.
Model data
The extent to which CH4 is released from an abandoned mine depends on the duration of time since abandonment. CH4 emissions are at their greatest immediately subsequent to abandonment and decrease through time thereafter.
Under this methodology, specific emissions factors are provided for each of the calendar years 1990-2016. These calendar years represent the year for which emissions are under consideration and is called the 'inventory year'. Each inventory year is represented by five emissions factors which describe the quantity of CH4 emitted during that calendar year by mines abandoned during each of the following historical time periods:
- 1901-1925
- 1926-1950
- 1951-1975
- 1976-2000
- 2001-present
Activity data required
Greenhouse gas emissions are directly proportionate to the number of mines under consideration. The number of mines abandoned during each of the five historical time periods must therefore be specified in order to calculate.
The specification of a volume of recovered methane can also be optionally provided.
Calculation and results
CH4 emissions for each of the five historical time periods are calculated according to the specified number of mines and the respective emissions factor. From the total CH4 emissions calculated, any CH4 recovered during the inventory year is then subtracted.
Two emissions quantities are ultimately provided, representing: CH4 and CO2e emissions. All emissions calculated by this methodology represent those attributable to the abandoned mines for the annual period under consideration, minus any CH4 which is recovered during that time.
Related methodologies
Other IPCC methodologies which focus on mining-associated fugitive emissions scenarios are available, covering underground and surficial active mines, the tier 2 methodology for abandoned underground mines, and methane flaring.
Where recovered methane is burned for energy production, flared, or fed into a gas distribution system, the IPCC methodologies for stationary fuel combustion, methane flaring and oil and gas processing may be of interest.