Underbalanced drilling

Better well control allows at-balance or even underbalanced drilling, resulting in higher penetration rates and reduced potential for formation damage. 

Initially glass microspheres were used in the 1970s to overcome severe lost circulation problems in the Ural Mountains. The technology has been used in other sites [1189]. Hollow glass beads reduce the density of a drilling fluid and can be used for underbalanced drilling [1199-1201]. Field applications have been reported [73]. 

K. Aguilar, R. Colina, M. Borrell, A. Aponte, and Y. Rojas. Evaluation criteria to formulate foam as underbalanced drilling fluid. In Proceedings Volume on CD ROM. ladc et al Underbalanced Drilling Conf (Houston, TX, 8/28-8/29), 2000. 

Biesman, T. Emeh, V. An Introduction to Underbalanced Drilling in Proc., 1st Underbalanced Drilling International Conference, The Hague, Netherlands, 1995. 

Argillier, J.-F., Saintpere, S., Herzhaft, B. and Toure, A. 1998. Stability and Flowing Properties of Aqueous Foams for Underbalanced Drilling. Proc. SPE Annual Tech. Conf, New Orleans, SPE 48982. 

Figure 1 depicts four fluids that are commonly used in lightweight or underbalanced drilling applications. Shown in each depiction is the drilling fluid, as it may appear down-hole with cuttings being carried from the borehole. These fluids include ... 

The acceptance of underbalanced drilling on the basis of explicit risk analysis, which had been banned under the detailed rules. 

In this run, we increase the F assumed in Run 2 one-hundred-fold to 0.000001 ft /lbf This represents a case where almost all of the surface production is assumed by borehole fluid expansion it simulates underbalanced drilling when substantial gas is released from solution into the wellbore column. This simulation was designed to test the stability limits and physieal correctness of the scheme. The results of this simulation lead to a very nonproductive reservoir as expected. For example, the following plot. 

Consider an underbalanced drilling situation where low pressures in the borehole release free gas at the shallower depths. Formulate a wellbore storage model for use in such highly compressible two-phase flows. 

G. H. Chitty 2002. Corrosion issues with underbalanced drilling in H2S reservoirs. SPEReprint Series... 

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