Drilling Cuttings(Solids) and Gas Removal Equipment In Mud Circulating System

500 shale shaker

The drilling cuttings removal equipment is often called solid-control equipment because it is mostly used for removing drilling cuttings in the mud returned from the borehole. Primary solid-removal equipment should include shale shakers, a degasser, a desander, a desilter, and a decanting centrifuge. All of these parts are installed on top of the mud tanks.

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Mud Agitator Impeller Size Calculation (Turnover Rate (TOR))

Turnover Rate (TOR)


Impeller sizes are determined by calculating the TOR (sometimes called the time of rollover) for each compartment. This is the time, in seconds, required to completely move the fluid in a compartment (Table 10.1) and can be calculated by knowing the tank volume and impeller displacement:

TOR = (Vt⁄D)×60

where

. Vt=tank volume, in gallons or liters
. D=impeller displacement, in GPM or LPM (as displayed in Table 10.2).

For flat and canted impeller applications, TOR should range between 40 and 85 seconds. As the TOR approaches 40 seconds, the chance for vortex formation and possible air entrainment increases. At values greater than 85 seconds, the proper suspension may be jeopardized and solids will begin to settle.

Table 10.1 Typical Turnover Rate Values, in seconds

Impeller TypeRemovalAdditionSuctionReservePill
Canted/flat50-7550-7565-8550-8040-65

Table 10.2
60-Hz Impeller Displacement D Values

Diameter Flat Canted Contour
InMmGpm1pmGpm1pmGPM1pm
20508105139789093441N/AN/A
246101941737416456226N/AN/A
2871128391074624689341586122185
32813463517543376414247N/AN/A
389657342277896343240081060440136
401016841131836728427570N/AN/A
421067N/AN/AN/AN/A1394052762
4411181130042771992837577N/AN/A
451143N/AN/AN/AN/A1681263633
481219144015450812512473582002075776
521321186307051516100609392485294063
541372N/AN/AN/AN/A27602104475
561422N/AN/AN/AN/A30353114887
601524N/AN/AN/AN/A36567138404
641626N/AN/AN/AN/A43533164771

For contour impeller applications, values must be significantly faster (i.e., smaller numbers) to achieve the same results, but because of the impeller design, air entrainment is less probable. In symmetrical compartments, the fluid has a nearly equal distance to travel from the center of the impeller shaft or from the impeller blade tip before it contacts the vessel wall. Agitators should be placed where the shaft is centered in the tank or compartment.

When defining the area in which to mix, it is best to work with symmetrical shapes like squares or circles (as viewed in a plan drawing or overhead view of the tank layout). Rectangular tanks should be converted to nearly square compartments if possible. Maximum fluid working volumes in compartments should not be higher than 1 foot (about 3⁄10 m) from the top of the tank. This will allow for a little extra capacity in emergencies, slightly out of level installations, and/or fluid movement on floating rigs.

Working volume for square or rectangular tanks is calculated by knowing dimensional values for length (L), width (W), and height (H; in feet for gallons, in meters for liters):

For gallons:

Vt = L × W(H− 1)× 7.481

The working volume for round tanks with flat bottoms is:
For gallons:

Vt = Π r²(H−1)× 7.481

For liters:

Vt = Π r²(H−0.3)×  1000

For round tanks with dish or cone bottoms, calculations for working fluid volume are based on straight wall height (i.e., this height is measured from the tank top to where the tank joins the cone or dish at the bottom). This leaves adequate free space above the maximum fluid operating level. In all cases, if H<5 feet (1.5 m), a radial flow impeller should be specified.