Page 18 - Shale Shakers Drilling Fluid Systems

Historical Perspective

Drilling fluid was used in the mid-1800s in cable Mud was circulated through these pits, and
tool (percussion) drilling to suspend the cuttings sometimes a partition was placed in the settling
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until bailed from the drilled hole. With the advent pits to accelerate removal of unwanted sand and
of rotary drilling in the water well-drilling indus- cuttings. This partition extended to within a foot
try, drilling fluid was well understood to cool the or two of the bottom of the pit, thereby forcing all
drill bit and to suspend drilled cuttings for removal the mud to move downward under the partition
from the wellbore. Clays were being added to the and up again to flow into the ditch to the suction
drilling fluid by the 1890s and by the time Spindletop pit. Much of the heavier material settled, by grav-
was discovered in 1901, it was considered neces- ity, in the bottom of the pit. With time, the pits
sary to have suspended solids (clays) in the drill- filled with cuttings and the fluid became too thick
ing fluid to support the walls of the borehole. to pump because of the finely ground cuttings
These solids (clays) resulted from the disaggre- being carried along in the drilling fluid. To rem-
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gation of formations penetrated by the drill bit. edy this problem, jets were placed in the settling
If the penetrated formations failed to yield suffi- pits to move the unusable mud to a reserve pit.
cient clay in the drilling process, clay was mined Then, water was added to thin the mud and drill-
on the surface from a nearby source and added ing resumed.
to the drilling fluid. These were native muds cre- In the late 1920s, drillers started looking to see
ated either by "mud making formations" or, as how other industries resolved similar problems. It
mentioned, by adding specific materials from a was discovered that ore dressing plants and coal
surface source. tipples were using:
Drilling fluid was recirculated and water was
added to maintain the best weight and viscosity 1. Fixed bar screens placed on an incline
for specific drilling conditions. Cuttings, or pieces 2. Revolving drum screens
of formation (small rocks) that were not dissolved 3. Vibrating screens
by water, required removal from the drilling fluid
to continue the drilling operation. Under the sole The latter two methods were adopted for remov-
discretion of the driller or tool pusher, a system of ing cuttings from drilling fluids.
pits and ditches was dug on-site to separate cut- The revolving drum, or barrel-type screens (called
tings from the drilling fluid by gravity settling (grav- trommel screens), were widely used with the early
ity forced the cuttings to deposit in the pits and low-height substructures. These units could be
ditches). This system included a ditch from the placed in the ditch or incorporated into the flow
well, or possibly a bell nipple, settling pits, and a line from the wellbore. The mud flowing into the
suction pit from which the "clean" mud was picked machine turned a paddle wheel that rotated
up by the mud pump and recirculated. the drum screen, through which the drilling fluid
passed. The screen used at this time was very
coarse, or 4 to 12 mesh. These units were quite
popular because no electricity was required and
the settling pits did not fill up as quickly. Today,
revolving drum units have just about disappeared.
The vibrating screen, or shaker, became the first
1 line of defense in the solids removal chain and for
For a discussion on cable tool drilling, read History of Oil Well
Drilling by J. E. Brantley. many years was the only machine used. Early shak-
2 ers were generally used in dry sizing applications
Bold-faced words are defined in the Glossary, pages 276-329.
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