Abstract: A new kind of lowOdensity system , which is called recyclable microOfoam drilligfluid , has been put forward recently both domestic and overseas. It has overcome most disadvantages of conventional foam system such as bad pumping and oneOoff use that may lead to lots of waste of agents and serious environmental pollution. Based on the theoretic analysis of formations
and stability of the microOfoam system , a physical chemistry model has been put forward in this paper. By a lot of experiments on the basis of the formation , stability and application conditions , a system that can accord with the hypothetical conditions has been obtained finally. The system has many advantages such as high stability , adjustable density (range from 0. 5
～0. 9 g/ cm3) , low filtrate and good ability to resist salt , calcium and temperature.

Key words: foam drilling fluid, microO foam, stability, microstructure, macroOcapacity