Page 224 -

186 Part III Underbalanced Drilling Systems

Illustrative Example 9.2 (Continued )
Drill string data
Length of heavy drill pipe below collar: 1,500 ft
Heavy drill pipe OD: 5 in
Heavy drill pipe ID: 3 in
Drill collar length: 480 ft
Drill collar OD: 6.25 in
Drill collar ID: 2.5 in
Drill pipe OD: 4.5 in
Drill pipe ID: 3.643 in
Material properties
Specific gravity of rock: 2.65 (water = 1)
Specific gravity of gas: 1 (air = 1)
Density of injected liquid: 8.4 ppg
Specific gravity of formation water: 1.05 (water = 1)
Specific gravity of formation oil: 0.85 (water = 1)
Pipe roughness: 0.0018 in
Borehole roughness: 0.1 in
Environment
Site elevation (above mean sea level): 50 ft
Ambient pressure: 14.7 psia
Ambient temperature: 60°F
Relative humidity: 0.1 fraction
Geothermal gradient: 0.01 F/ft
Friction tuning factor: 8
Operating conditions
Surface choke/flow line pressure: 14.7 psia
Rate of penetration: 120 ft/hour
Gas injection rate: 1,000 scfm
Liquid injection rate: 100 gpm
Formation water influx rate: 1 bbl/hour
Formation oil influx rate: 1 bbl/hour
Bit orifices: 20-1/32nd in
20-1/32nd in
20-1/32nd in

Solution
This problem can be solved with computer program FoamDrill-09.xls.
The results are shown in Figures 9.7 through 9.11.