Key potential environmental impacts
Water
Water production associated with dewatering coal seams and shale beds
What is the issue?
With many NGC (coalbed methane) projects, particularly those in the Powder River Basin in the United States, significant quantities of water must be produced to de-pressure the coal seam and allow the NGC to flow. The quality of the water varies from usable to saline, and disposal of the water must be responsibly managed. In some areas of the United States surface disposal of water without water or soil treatment could negatively alter soils and vegetation due to high levels of salt, sodium, and trace elements. There is also the risk of impacts on aquatic life and of erosion if the water is disposed of in existing water bodies even if the water is fresh.
What is industry doing?
Water production in Canada may not be as significant as it has been elsewhere.
There are three types of NGC (coalbed methane) plays in Canada:
-
"Dry" coal with insignificant produced water - In the case of dry coals, the coal seams do not contain significant water volumes, either saline or fresh. Consequently, dry coal reservoirs do not require dewatering to reduce the reservoir pressure and release the gas and allow it to flow. These "naturally" dewatered coals contain free gas upon discovery, although at a lower pressure than normal.
-
Coals that produce unusable brine - In the case of coals that produce unusable brine, the produced saline water is reinjected into deeper zones not connected with shallower fresh water aquifers, in accordance with regulations already in place which govern conventional gas production. These underground formations are deep and not connected to any fresh water sources. Injection poses no threat to groundwater, fish habitat or local vegetation because drill holes are lined and cased with cement from the injection level to the surface. Large amounts of such water have been handled and disposed of for years without major incident as part of the conventional oil and gas industry.
-
Coals that produce usable water - To date, coals that produce usable water are rare in Canada. Current Alberta regulations regarding the production and disposal of usable water associated with coal seams are designed to protect the usable water rather than to recover the NGC (coalbed methane). Co-production of usable water and NGC on a commercial scale in Alberta will require regulation changes to optimize management of both these valuable resources. British Columbia has established guidelines that allow for co-production of usable water and NGC within the capacity of local watersheds.
Prior to allowing water disposal into surface drainage, the water must meet strict environmental standards to ensure compatibility with soils and vegetation. In addition to water quality, water quantity and potential use are also taken into consideration.
previous | next