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Underbalanced Drilling Operations 219

2400
190
2300
170
2200 150
Bottomhole Pressure (psia) 2000 BHCP 130 Choke Pressure (psia)
2100

WHP
1900
110
1800

1700 90
70
1600

1500 50
0 10 20 30 40 50 60 70 80 90 100
Time (min)
Figure 10.7 A field example showing pressure fluctuation during a pipe connection.

10 Liquid Injection Rate=0.9m /min
Pressure Gradient (kPa/m) 8 6 4 Change in bottom pressure with 3
3

100 kPa change in surface pressure

Liquid Injection Rate=0.1m /min

2
0 10 20 30 40 50 60
3
N Injection Rate (m /min)
2
Figure 10.8 Effect of liquid injection rate on pressure fluctuation at the bottomhole.

fluctuation at the bottomhole. The pressure fluctuation in aerated liquid
drilling has detrimental effects on both drilling operations and resultant
well productivity. It can cause borehole collapse problems and excessive
reservoir fluid influxes that need handling during drilling. It also induces