Page 167 - Environmental Control in Petroleum Engineering

154 Environmental Control in Petroleum Engineering

to discourage disposal of refuse, paper, and other household trash in
pits. These household wastes should be collected and stored separately
for off-site disposal. Sanitary wastes should be collected and treated
to satisfy state and local effluent requirements using septic systems,
portable commercial containers, shipment to municipal sewage facili-
ties, or disposal at municipal solid waste sites. Leaks and spills from
all equipment should be eliminated. Liners, drip pans, or basins can
be used to collect any potential spillage from equipment. Equipment
that is leaking should be repaired or replaced. Drilling rigs should be
washed at a site only if absolutely needed and only with recycled pit
or sump water, not with fresh water.
Optimized drilling operations provide a significant opportunity for
minimizing wastes. Because the total volume of drilling wastes is
controlled primarily by the hole size and well depth, the smallest
diameter hole should be drilled to minimize the volume of cuttings
generated and drilling mud used. The needs for future recovery activi-
ties, including possible multiple tubing strings for improved recovery
operations, must be considered when determining the hole size. Inter-
mediate casing strings can be used to isolate problem zones, e.g., salt,
high pressure, or reactive shales, and minimize the volume of special-
ized drilling mud needed to drill below those zones. Hole washout can
be minimized during drilling by limiting the recirculation rate of
drilling fluids such that the annular velocity to lift cuttings is not
excessive. During drilling, the surge and swab pressures in the well-
bore should be minimized by limiting rapid pipe movement to maintain
a good mudcake and prevent further hole enlargement.
A number of drilling mud systems are available. Closed-loop sys-
tems with good solids control and separation equipment can be used
to minimize the volume of drilling wastes. In these systems, covered
steel tanks are used instead of digging reserves pits in the ground.
Advanced solids separation and dewatering equipment must be used,
however. Drilling fluid systems and fluids should be designed to
minimize drilled-solids degradation and reduction of particle size. The
bottom of the mousehole should be cemented to prevent drilling fluids
from leaching into groundwater when the kelly is in place.
Reserves pits can be constructed to minimize the volume of wastes.
They should cover a limited area to control the amount of rainfall
entering them, but they should also have sufficient capacity so they
do not overflow during heavy rains. In many areas, pit liners are