Page 267 -

230 Part III Underbalanced Drilling Systems

SUMMARY
This chapter presented a brief introduction to the UBD operations
with aerated liquids and foams. Pressure stability in aerated liquid drilling
can be improved using annular injection of gas and increasing the mix-
ture flow rate. Annular injection of gas also allows for conventional
MWD to be used in directional drilling. Foam stability can be enhanced
by adjusting injection GLR and backpressure. When the hole depth is
greater than 5,000 ft, where foam is not expected to be stable, a higher
mixture flow rate should be used for hole cleaning purposes.

REFERENCES
Guo, B., Ghalambor, A., 2006. Characterization and analysis of pressure instability in
aerated liquid drilling. J. Can. Pet. Technol. (June).
Guo, B., Sun, K., Ghalambor, A., 2003. A closed form hydraulics equation for predicting
bottom-hole pressure in UBD with foam. In: Paper SPE 81640, Proceedings of
IADC/SPE Underbalanced Technology Conference and Exhibition, March 25–26,
Houston.
Sanghani, V., 1982. Rheology of foam and its implications in drilling and cleanout
operations. M.S. Thesis, University of Tulsa.

PROBLEMS
10.1 Solve Illustrative Example 10.1 assuming a 7⅞-in bit size and a
4½-in drill pipe OD.
10.2 Assuming T = 560 °R, reproduce Figure 10.13.
10.3 Assuming T = 560 °R, reproduce Figure 10.14.
10.4 Assuming T = 560 °R, reproduce Figure 10.15.