An increasing amount of natural gas is being produced from unconventional sources in North America. In the past, shale formations and coal-bed seams containing natural gas were too expensive to develop. Advances in drilling technologies and multi-stage hydraulic fracturing mean that these unconventional gas deposits can now be cost-effectively accessed.
The two main types of unconventional natural gas deposits are coal bed methane extracted from coal seams and shale gas found in silt or sand beds locked within shale formations. To produce shale gas, water or other fluids are injected into gas reservoirs at high pressure. The water creates fractures in the rock that allow natural gas to flow upward to the well.
Shale gas reservoirs are typically form 2,000 to 3,000 metres below the surface. Drinking water aquifers are usually found at depths of less than 300 metres. Freshwater aquifers are protected by provincial government regulations that apply to all types of industries. If a natural gas well is drilled through an aquifer, special measures are taken to protect the water. A steel casing is cemented in place to isolate the natural gas well from the water.
Unconventional gas deposits are widely spread across North America. In Canada, unconventional deposits have been identified in several provinces. It is in the Horn River and Montney regions in northeastern British Columbia that are located the first major shale deposits to be developed in Canada.