Page 409 - Air and Gas Drilling Manual

installed in the return flow line at the end of the line that is attached to the BOP
stack. These valves have an inside diameter of 5 9/16 inch. Determine the
approximate minimum volumetric flow rate of the drilling mud that will be needed
for this aerated drilling operation. Chapter 9: Aerated Fluid Drilling 9-13
The incompressible drilling fluid to be used for this aerated drilling operation is
to be a standard fresh water drilling mud with plastic fluid properties. As has been
argued above, the drilling mud properties and flow characteristics will be designed to
clean, lift, and suspend the rock cuttings. The plastic viscosity (30 cps) and the
2
plastic yield stress (5 lb/100 ft ) are typical drilling mud properties that enhance
bottomhole cleaning, lifting, and suspension of rock cuttings. With the above data.
determine the drilling mud minimum volumetric flow rate required to clean the well.
The incompressible fluid to be used in this illustrative example is a water base
drilling mud with plastic properties. Therefore, the minimum volumetric flow rate
of the incompressible drilling fluid is determined using Equations 9-1, 9-2, 9-3a, 9-
5a, and 9-6 above (transition flow is assumed not to exist). The anticipated drilling
rate is 60 ft/hr. Using Equation 9-2, the critical concentration velocity is
60
V c
,
3 600 0 04)
(
.
.
V c 0 417 ft/sec
The specific weight of the sedimentary rock to be drilled is approximately
7
2
(. ) (62 .)
4
s
168 5 lb/ft 3
.
s
where the specific gravity of sedimentary rock is assumed to be approximately 2.7
(see Chapter 6). The specific weight of the 10 lb/gal drilling mud in consistent
units is (subscript f is replaced by m)
()
10 12 3
m
231
75 0 lb/ft 3
.
m
The absolute plastic viscosity of the drilling mud in consistent units is

(.
0 02089)
30 0 001) (.
mp
lb sec
.
0 0006267
mp 2
ft