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Kansas Geological Survey, Open-File Rept. 96-1a
Proposed Management Areas--Page 9 of 16

Surface-Casing Requirements for Oil and Gas Wells

Kansas regulations also require the petroleum industry to protect fresh and usable aquifers from contamination by establishing minimum depths for surface casing in an oil or gas borehole (Table 1 of the General Rules and Regulations for the Conservation of Oil and Natural Gas of the KCC). The surface casing is a pipe that is inserted into the borehole being drilled during oil or gas exploration and sealed by injecting cement under pressure to fill the space between the casing and the borehole. The primary function of the surface casing in the petroleum industry is to prevent saltwater from entering a usable aquifer from lower zones intersected by the borehole. Although the static fluid level in some of the formations underlying the Dakota aquifer can be below the bottom of the aquifer, the fluid level can often be above the aquifer base in some areas such as where saltwater intrudes from the Cedar Hills Sandstone into the base of the Dakota in central Kansas. In other areas, pressures have been increased in the petroleum bearing strata by the injection of secondary or waterflood waters or in brine disposal zones by disposed saltwater. The greater pressures could also lead to flow of saltwater into overlying aquifers if the aquifer sediments were not sealed along the borehole. The cemented surface casing has the added advantage of protecting fresh and usable aquifers from surface contamination and from loss of water resources by drainage down boreholes where fluid levels in deeper formations are below the aquifer.

State statutes define the classifications for the fresh and usable aquifer waters that must be protected:

Class I--Fresh ground water contains not more than 500 mg/L chloride or 1,000 mg/L of total dissolved solids.
Class II.--Usable ground water contains more than 500 mg/L but not more than 5,000 mg/L chloride or more than 1,000 mg/L but not more than 10,000 mg/L total dissolved solids.
Class III--Mineralized ground water contains more than 5,000 mg/L chloride or more than 10,000 mg/L total dissolved solids.

The map of total dissolved solids (Figure 3) includes contour lines for both the 1,000 mg/L and 10,000 mg/L TDS values for the limits of fresh and usable waters. Figure 3 was produced to generally display the freshest water within the aquifer and can serve as a conservative estimate of what waters should be protected. The data for this figure are based on analyses of water samples primarily in the fresh to usable water areas and on interpretation of geophysical logs in northwest Kansas. The Table I statutes for minimum surface casing requirements were established using data preceding the Dakota Aquifer Program. Figure 3 provides improved information on which future revisions of Table I could be based.

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Kansas Geological Survey, Dakota Aquifer Program
Original report available from the Kansas Geological Survey.
Electronic version placed online July 1996
Scientific comments to P. Allen Macfarlane
Web comments to webadmin@kgs.ku.edu