New Research of Borehole Wall Protection Technology in Ocean Scientific Drilling

Abstract In the process of ocean scientific drilling, borehole accidents (e.g., borehole collapse, burying of drill tools, and sticking of drill tools) are often caused by borehole wall instability in loose and broken strata. It is very difficult to deal with such accidents, and the drill pipe in the borehole has to be discarded in serious cases. Therefore, the stability of the borehole wall seriously affects the drilling quality and efficiency. At present, there are three effective methods of ensuring wellbore stability: casing, drilling fluid, and agent plugging technology. Casing can effectively prevent instability of all types of unstable formations and can isolate different pressure zones. Using the proper drilling fluid can control drilling fluid loss, reduce free water infiltration into the borehole wall, and form a thin and dense mud skin, which is conducive to the stability of the borehole wall. Agent plugging technology, especially chemical gels, is mainly aimed at the broken zone. After entering the formation, it makes the entire broken zone form a single high strength unit, improves the cementation ability of the lost formation, and improves the sealing and bearing capacity in order to achieve the purpose of sealing and plugging of leaks. In this paper, the present situation, technical principles, and technological processes of wall protection technology in ocean scientific drilling are summarized, and the different types of wall protection technology were researched and tested. The results of this study provide a reference for international ocean scientific drilling in the future.