Page 39 - Air and Gas Drilling Manual

1-16 Air and Gas Drilling Manual
drill collars, and ~ 9,500 ft of API 4 1/2 inch diameter, 16.60 lb/ft nominal, EU-
S135, NC 50, drill pipe.

Figure 1-15: Comparison example well and drill string.
The mud drilling hydraulics calculations are carried out assuming the drilling
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mud weight is 10 lb/gal (75 lb/ft ), the Bingham mud yield is 10 lb/100 ft , and the
plastic viscosity is 30 centipose. The drill bit is assumed to have three 13/32 inch
diameter nozzles and the drilling mud circulation flow rate is 300 gals/minute.
Figure 1-16 shows the plots of the pressures in the incompressible drilling mud as a
function of depth. In the figure is a plot of the pressure inside the drill string. The
pressure is approximately 1,400 psig at injection and 6,000 psig at the bottom of the
inside of the drill string just above the bit nozzles. Also in the figure is a plot of
the pressure in the annulus. The pressure is approximately 5,440 psig at the bottom
of the annulus just below the bit nozzles and 0 psig at the top of the annulus at the
surface.
The pressures in Figure 1-16 reflects the hydrostatic weight of the column of
drilling mud and the resistance to fluid flow from the inside surfaces of the drill