An aeration foam drilling fluid used in underbalanced drilling

Underbalanced drilling means that drilling fluid pressure is less than reservoir pore pressure, and its technical key is the drilling fluid density controlling. An aeration foam drilling fluid used in underbal-anced drilling is presented. The fluid is a three-phase system composed of air, liquid and solid and its foa- ming agent is DF and stabilizing agent is a common organic high molecular polymer. A group of formulations have been optimized based on cross experiments on the dosage of clay, polymer and foaming agent according to underbalanced requirements. In both aspects of solid mineral exploration and hot gas field development , the fluid has been effectively used and results showed that the fluid has many advantages such as stable foam, low density, low liquid pressure, good rheology property, strong ability for carrying cuttings, high thermal stability, strong inhibition and good resistance to fouling. The drilling fluid can be used as a testing medium of underbalanced drilling in field.