Most Class II injector wells are for enhanced oil recovery, such as waterfloods. About 20 percent of Class II wells are used in waste disposal, to dispose of produced water, usually brine, into deep formations below the base of fresh water.Underground Injection Control, accessed 4 February 2015.
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As production began its inevitable decline with the exhaustion of easily recovered oil, and consequent drop in reservoir pressure, drillers began trying secondary recovery techniques. Gas injection was used from 1947 in the west part of the field, and several waterfloods were attempted as well.DOGGR, 94 Peak oil production from the entire Cat Canyon field was in 1953, coinciding with development of newly discovered pools and enhanced recovery techniques in existing drilling operations.
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The Energy Information Administration (EIA), the statistics service of the Department of Energy, estimated in 2013 that there were 1.6 billion barrels and 2.2 trillion cubic feet (tcf) of technically recoverable oil and natural gas in the Canadian portion of the Bakken formation.US Energy Information Administration, World shale gas, 17 May 2013. Crescent Point Energy and other operators are implementing waterfloods in the Bakken Formation of the Viewfield Oil Field in Saskatchewan. Some believe that waterflooding can raise the recovery factor at Viewfield from 19 percent to more than 30 percent, adding 1.5 to two billion barrels of additional oil.
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There are three primary techniques of EOR: gas injection, thermal injection, and chemical injection. Gas injection, which uses gases such as natural gas, nitrogen, or carbon dioxide (CO2), accounts for nearly 60 percent of EOR production in the United States. Thermal injection, which involves the introduction of heat, accounts for 40 percent of EOR production in the United States, with most of it occurring in California. Chemical injection, which can involve the use of long-chained molecules called polymers to increase the effectiveness of waterfloods, accounts for about one percent of EOR production in the United States.
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Various enhanced oil recovery techniques were used in the Weyburn field prior to the introduction of CO2, between the 1970s and 1990s. These include additional vertical drilling, the introduction of horizontal drilling, and the use of waterfloods to increase pressure in the reservoir. In October 2000, Cenovus (formerly Pan Canadian, Encana) began injecting significant amounts of carbon dioxide into the Weyburn field in order to boost oil production. Cenovus was the operator and held the largest share of the 37 current partners in the oilfield prior to the sale of local assets to Whitecap in 2017.
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Land degradation results in canyons like this one that cuts the loess plateau in Linxia County, Gansu. Reduced moisture suction due to a degraded vegetation layer formed this creek flowing into the lower Daxia River. Sichuan pepper shrubs planted on terraced gulch slope, to slow down erosion and utilize the land (Linxia City, Gansu). Soil erosion and waterfloods swell up the rivers with brownish waters—a suspension of silts, clays and other soil particles The Loess Plateau was formed over long geologic times, and scientists have derived valuable information about global climate change from samples taken from the deep layer of its silty soil.
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