As the supply of gas from conventional sources is depleted, the prospect of gas from unconventional resources will become attractive. These sources include enhanced recovery from water drive gas reservoirs, tight gas formations. Replacement/recycling gas schemes, and coal-bed methane. Estimates of the quantity of natural gas occurring in these sources vary considerably; even more uncertain is the amount of natural gas which can be produced commercially now and in the future. However, with the application of appropriate technology, these sources can augment the supply of natural gas in the short and specially the long term.
This paper attempts to describe the resources, their potential and associated production technology. Much of the effort has been focused on enhanced recovery from water drive gas reservoirs. The mechanism of gas trapping in such reservoirs is analyzed and ways to enhance gas production are described. Water coning in gas reservoirs and methods to control it are discussed. Nitrogen injection for improved recovery is briefly described. Finally recovery of gas from tight gas reservoirs and coal beds is outlined.
Enhanced gas recovery is used to describe the recovery of unconventional, deep, or otherwise difficult-to-recover natural gas. Unconventional natural gas is the gas contained in geologic formations which have not been exploited traditionally by the oil and gas industry and include tight gas sands, Devonian shales, formations with active aquifers, coal bed methane, etc.. A number of these geologic formations are known to contain sizable quantities of natural gas. However, these resources are not being fully developed because of economic and technological limitations.
Canada's current natural gas supply is primarily from conventional resources. However, as this production declines over time, the nation will become increasingly dependent on higher cost resources as well as unconventional gas supply. Increased demand for natural gas as an environmentally friendly resource will also lead to the development of unconventional resources. In the past, the price of natural gas did not encourage production from these resources. With the anticipated increase in price and value of gas, recovery of such reserves is getting more attention.
With appropriate research and development, exploitation of these resources can begin in the near term with expanded commercial production in the long term. Unconventional gas is currently produced from the higher quality tight gas sands, Devonian shales and watered-out reservoirs in the United States. However, gas recovery technology is inefficient and inadequate for unlocking the vast bulk of the more difficult, lower grade resource. The technical challenges vary by type of unconventional resource and each type requires improvements in the knowledge base, the controlling characteristics as well as advances in well completions and stimulation technology. The size of the gas potential from unconventional sources, to a large extent, is dependent on how rapidly the technologies develop.
Unconventional natural gas comes from a variety of geographic and geologic formations and include the following:
Tight sand formations. Large amounts of potentially recoverable natural gas exists in low-permeability sandstone formations located in the western Canadian sedimentary basin IWCSB).
