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The main goal in selection of a subsurface disposal site is that the waste be emplaced in such a manner that it is isolated from freshwater supplies and the biosphere during its hazardous life. This can be accomplished only through detailed investigation of the lithology, porosity, permeability, thickness, lateral extent, depth, fluid content, and compatibility of a potential reservoir. Additional data for the area around a potential disposal site are also needed concerning the structure, geologic framework, confining rocks, hydrology, mineral resources, and the presence of boreholes or other excavations.
Rock types that are most desirable for subsurface waste disposal in Oklahoma are porous and permeable sedimentary rocks, such as sandstone, limestone, and dolomite, although fractured shale or mined caverns in shale and salt may also be suitable. Thick sequences of sedimentary rock make up most geologic provinces in the state, and it appears that most areas are underlain by reservoir rocks that locally can safely contain industrial wastes.
Major sandstone reservoirs that are locally capable of accepting liquid wastes include the Simpson Group, Springer Formation, Pennsylvanian sandstones, granite wash, and Permian sandstones; major carbonate reservoirs include the Arbuckle Group, Hunton Group, Mississippian limestones, Brown dolomite, and Permian dolomites. Where used for waste disposal, these reservoirs typically have porosities ranging from 5 to 20% and permeabilities ranging from 20 to 2,000 md.
At present, 17 wells are being used in Oklahoma to inject acids, caustics, solvents, process waters, salt water, paints, urea, detergents, metal-bearing solutions, and cement slurries into reservoirs 385 to 7,350 ft (116 to 2,205 m) below the surface. Most facilities inject at average rates of 40,000 to 400,000 gal/day and with injection pressures that range from 380 to 450 psi (2,618 to 3,100 kPa).
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