Page 168 - Environmental Control in Petroleum Engineering

Planning for Environmental Protection 155

required if saltwater- or oil-based muds are used. Liners should be
considered in sensitive areas, even if not required by current regula-
tions. Netting may be required over pits to prevent birds from landing
in them, particularly if the pits contain floating hydrocarbons.
Because many different fluids are found at most drill sites, a
managed pit system with multiple pits can be used to keep the different
fluids separated (Hall et aL, 1991; Pontiff et al., 1990). For example,
one pit could be used for mud reserves, one for cleaned cuttings, one
for skimmed oil, one for kicks, and one for storm water runoff. If
different mud types are used for different parts of the well, e.g., when
drilling through an overpressured layer, a salt dome, or other very
sensitive formation, a separate pit can be used for each mud type. One
pit can be used for drilling the top section of the well where native
materials can be used with minimal additives and one pit can be used
for drilling through the productive horizon, particularly for horizontal
wells. These systems minimize the total volume of materials having
the greatest potential for environmental impact. With a managed pit
system, different materials can be disposed of in the best way, mini-
mizing the volume of materials that must be disposed of at the highest
cost and reducing future liability.
Preplanning is important when developing a mud for each well.
When selecting a mud, detailed questions should be asked to the sales
representative about exactly what the various additives will do and
whether they are actually necessary for a particular well. Mud additives
can be pilot tested in small volumes to ensure they behave as claimed.
Inhibitive mud should be used to minimize hole enlargement during
drilling from the hydration of shales. Mud density changes should be
avoided because these normally require discarding some of the mud
and reformulating the remainder; this leads to an increase in the total
volume of mud that is used.
A number of operational changes during production can also be
implemented to minimize the total volume of waste generated. Routine
inspection and/or pressure testing of all tanks, vessels, gathering lines,
and flow lines should be scheduled. Routine inspection and/or auto-
matic pumps should be installed in all sumps.
Unfortunately, the largest volume of production waste is produced
water and little can be done to minimize its production. In some
formations, coning of water can be minimized by dually completing
a well in both the water and oil zone. This can limit water coning