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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Table of Contents
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
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