Page 21 - Shale Shakers Drilling Fluid Systems

4 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

A Mud Cleaner in the First Field Application. The mud cleaner consisted of
a bank of 20, 4-inch Pioneer hydrocyclones mounted above a stainless steel,
double-deck, round Sweco shaker. The mud cleaner was used during 40 days
of driling from 11,000 to 16,000 feet, with 11 ppg mud, through gas sands with
formation pressures equivalent to 2.2 ppg mud weight. Stuck pipe and lost
circulation experienced on earlier wells was eliminated. The mud cleaner was
deactivated for drilling from 16,000 to 16,200 feet to "find" a caseing seat.
Torque and drag on the drill string increased significantly, and wiper trips with
the drill string were required between logging runs. The mud cleaner was re-
activated and "cleaned" the drilling fluid for one circulation through a 150 x 150
mesh screen, followed by one circulation using a 200 x 200 mesh screen be-
fore running 9|-inch casing in a 121-inch hole. No problems were encoun-
tered whie running the casing or during the cementing operation.

A more recent development, introduced in the mixed polymers injected into the feed line of the
1980s, is the linear shaker. Developments in screen centrifuge causing flocculation. The solids are
technology have made it possible for pretensioned coalesced inside the centrifuge resulting in separa-
screens to be layered for obtaining very precise tion of solids from the liquid, and the solids are
cuts while still maintaining an economical screen then discarded.
life. Linear motion is the best conveying motion A recent innovation for environmental purposes
to move the solids off the screen, and it is pos- and more liquid retention, is the dryer. The dis-
sible to convey cuttings "uphill." Screens can be charge from linear shakers, desanders, and desilters
elevated to retain the cuttings longer to obtain a is flowed across another linear shaker with even
dryer-reduced liquid content discharge. Also, finer finer screens (down to 450 mesh, or 32 microns)
screens, with smaller openings, can be used on the and usually a larger screening surface. Any liquid
linear motion shaker. One application of linear that escapes can be retained in the sump. The
shakers is to screen the underflow from desanders sump pump returns the liquid to the active system,
and desilters rather than using a mud cleaner. This usually to the centrifuge feed tank.
device is called a "mud conditioner." These systems, or combinations of the various
Present technology includes liquid salvage— items discussed above, meet most environmental
dewatering or solids flocculation—that strips the requirements and conserve expensive liquid phases.
liquid phase from solids and returns an almost The desirable effect is to close the loop on liquid
clear stream of water into the mud system. This discharges, leaving a damp, semi-dry solid mass
process includes a decanting centrifuge with pre- to remove for disposal.