Page 182 - Shale Shakers Drilling Fluid Systems
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DILUTION 165
3. The removal efficiency of the solids con- removal equipment determines the quantity of
trol arrangement can vary significantly de- drilling fluid that must be built to maintain a tar-
pending on the adherence to sound arrange- geted drilled-solids concentration and a constant
ment practices and operating conditions. Many pit volume. These representative calculations
drilling rigs with poor solids management describe the fate and effect of 100 barrels of drilled
have trouble reducing the mud weight below solids arriving at the surface. (Note, this may
9.7 ppg. While others can comfortably create not correspond to generating 100 bbl of borehole
an 8.8 ppg drilling fluid. This is related to the because of lag time and solids storage in the well-
removal efficiency. API RP13C provides a bore.) The first set of calculations is based on a
new method of following a tracer to deter- solids removal section that is removing 100%, 90%,
mine the solids removal efficiency. In the or 80% by volume of the drilled solids, with the
following section, a second method is targeted drilled solids level set at 4% volume. For
presented. These methods can be used this comparison, assume 100 bbl is approximately
while drilling a reasonably deep hole (such the volume of 1,000 feet of a 10-inch diameter
as 1,000 to 2,000 feet). The analysis assumes hole. This analysis is the basis for calculating the
that no drilling fluid is jetted from the sys- minimum desirable removal efficiency. It also shows
tern. The removal efficiency of the system in the minimum quantity of new drilling fluid and
an unweighted drilling fluid is usually higher minimizes the volume of discarded fluid. These
than in a weighted drilling fluid. Solids in the calculations assume no migration of fluid to or
same size range as the weighting material from the wellbore, no rock compressibility, and no
cannot be removed with known technology. gas migration to the surface. These example cal-
culations also assume that the removed drilled
solids concentration is 35% by volume.
In the case of 100% removal efficiency, all
EFFECT OF DRILLED SOLIDS of the drilled solids reaching the surface are
REACHING THE SURFACE removed along with 65% drilling fluid volume. The
pit levels will decrease by the volume of drilled
Calculations, summarized in Figures 8-1 through solids and drilling fluid removed from the system
8-3, illustrate how the effectiveness of the solids (286 bbl as shown in Figure 8-1). Although no
FIGURE 8-1. 100% solids removal efficiency.
