Treatment of Formation Water Invasion in Air Drilling

A serious concern in air drilling is the invasion of formation water into the hole, viscosifying the dry cuttings into viscous lumps which are adhered at the surface of the drill string and borehole wall, resulting in pipe sticking. Based on the mechanism that fluid with low surface tension can penetrate fast into and break the lumps, 9 surfactants was selected for the evaluation of their osmosis, and dispersing performance using static measurement of surface tension, wetting angle measurement, timing-area method, area measurement in specific time span, round fabric method, hot rolling test method and particle size distribution measurement. The 9 surfactants tested all had wetting ability. Surfactants with smaller hydrophobic groups in their molecular structures had strong osmosis. The dispersity of anionic surfactants is governed by the electric double layer theory, while the dispersity of nonionic surfactants is governed by steric effect. High molecular weight polymers have better dispersity than common surfactants. Laboratory experimental results showed that diesel oil treated with CJY had strong osmosis and dispersity, making it a better chemical in disintegrating mud lumps than oil based pipe sticking agent JKZ. Diesel oil treated with CJY performed better at elevated temperatures. This study provides a method for the solution of formation water cut during air drilling.