The circulating utilization of foam fluid is available, which was based on some of the lower carbon alcohols presenting the characteristics of both strong defoaming and weak restricting foam ability, and through optimum selection of formula by indoor experiments. The recirculable feature of four kinds of alcohols on unstable foam (0.6%K12), stable foam (0.6%K12+0.2%XC+0.2%HV-CMC) and stiff foam (0.6%K12+0.2%XC+0.2%HV-CMC+5.0%bentonite) was comparatively investigated. The circulating foam ability of the mixed system of alcohol D and tributyl phosphate (TBP)was studied on the self-made foam fluid circulation experimental device. The results show that alcohol D is the most suitable defoamer in four kinds of alcohols. The mixed system of alcohol D and TBP can recycle stable foam at least 8 times. With increasing cycle number, both foam volume and half life decrease, in which foam volume falls gradually and half life declines more dramatically. After 8 runs, the volume of foam falls from 470ml to 420ml and half life declines from 28.7min to 15.8min, but both of them can fill the actual requirements of on-site drilling.

This paper is the first in a series of studies designed to bring forward foam circulating utilization in underbalanced drilling by adding alcohol as defoamer. The goal is to understand the mechanism of foammg-defoaming-refoaming of alcohol better, and extend air foam drilling techniques in suit region.

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