Page 111 -

88 Part I Liquid Drilling Systems

Illustrative Example 4.1
For the data in Illustrative Example 3.2, select a liner size for two TSC
WF700 Triplex pumps. Assume the flow rate exponent m =1.75and the
maximum bit hydraulic horsepower criterion. Additional data are given as
follows:
Cuttings specific gravity: 2.7 (water = 1)
Particle sphericity: 0.85 (ball = 1)
Rate of penetration: 90 ft/hr
Rotary speed: 70 rpm
Cuttings concentration: 10%
Solution

1. For the given borehole geometry and fluid properties, the minimum flow
rate required to transport drill cuttings to the surface is calculated using
computer program Minimum Flow Rates.xls. The result is
3
q min = 137 gpm ð0:52m /minÞ
2. The designed flow rate in Illustrative Example 3.2 is
3
q des = 300 gpm ð1:14m /minÞ
The safety factor is 2.2.
3. The manufacturer’s pump specifications in Table 3.6 show that several
liner sizes meet this designed flow rate. The liner size of 5 in (0.127 m)
can be a good candidate. Two pumps with this liner size will provide
3
mud flow rates between (2)(155) = 310 gpm (1.18 m /min) and (2)(326) =
3
652 gpm (2.48 m /min) at pumping speeds from 71 spm to 150 spm.
3
4. Based on the designed flow rate of 300 gpm (1.14 m /min), the expected
total parasitic pressure loss at a depth of 9,950 ft (3,036 m) was calculated
in Illustrative Example 3.2 as
Δp d = 1,087 psi ð7,394 kPaÞ
5. Equation (3.6) gives

p p = ðm + 1ÞΔp d = ð1:75 + 1Þð1,087Þ = 2,989 psi ð20,333 kPaÞ
6. The manufacturer’spumpspecificationsinTable 3.6showthatthe maxi-
mum allowable pressure for the 5-in (0.127-m) liner is 3,362 psi (22,869
kPa). This pressure is greater than the calculated pump pressure of 2,989
psi (20,333 kPa).
7. The pressure safety factor is (3,362)/(2,989) = 1.125. Thus, the liner size of
5 in (0.127 m) can be selected for drilling this hole section.