In the Williston basin region, deep-well disposal of industrial fluid wastes is confined largely to the Saskatchewan part of the stable, relatively shallow, tectonic shelf, which is flanked on the south by the deeper basin proper, and is delimited in the north by the Canadian shield.

As of mid-1973, 30 industrial disposal wells had been drilled in Saskatchewan: 20 were in operation, 5 suspended, and 5 abandoned. To year-end 1972, more than 118.995 million bbl of fluid wastes, exclusive of oilfield brines, had been injected into subsurface aquifers in Saskatchewan: (1) waste brines (63,440,000 bbl), resulting from shaft and solution mining, as well as experimental solution of Devonian potash deposits; (2) waste brines (50,930,000 bbl), produced during solution mining of caverns in Devonian halite for subsequent storage of liquefied petroleum gases and dry natural gas; (3) refinery effluent (3,530,000 bbl), comprising sour water and spent caustic from 2 plants; and (4) brines containing small amounts of mercury compounds

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(221,000 bbl) from a chlor-alkali plant, associated with previously injected wastes (874,000 bbl) from production of the herbidices 2, 4-D, and MCPA.

The depths of injection intervals range from 1,448 to 4,692 ft. The maximum total depth of a disposal well in Saskatchewan is 5,536 ft. Average injection rates are from 3 to 1,100 US gpm and average well-head pressures vary from the sole influence of gravity to 1,750 psig. More than 44.13% of all industrial wastes injected into the Saskatchewan subsurface are received by clastic aquifers. In 18 injection systems, clastic units (Cambrian and Ordovician; Lower Cretaceous) are the disposal intervals, whereas 13 wells have been completed for disposal into carbonate units (Silurian to Mississippian). There are four multizone completions, each involving disposal of potash brines into a Silurian carbonate aquifer and an Ordovician clastic aquifer. In three disposal systems, mercury compounds are permitted to accumulate in caverns in Devonian evaporite strata.

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