Applications of MPD technology in offshore ultra-HTHP wells

Due to complex geological origins, the Yingqiong Basin of South China Sea is characterized by high formation temperature, high formation pressure, many pressure steps and narrow pressure window, which often lead to complex accidents in the process of drilling and completion in this area, such as kick, leakage and even the coexistence of kick and leakage. As a result, some wells in this area are faced with many operation difficulties and the costs are always high. Managed pressure drilling (MPD) can accurately control the bottom hole equivalent circulating density (ECD) and reduce the risk of well control and lost circulation in narrow pressure window formation so as to ensure the safe and efficient drilling. The MPD technology for onshore high temperature and high pressure (HTHP) wells has already been applied in many blocks (e.g. Tarim and Sichuan) and a set of mature technical system has been formed. In this paper, based on the actual situations of offshore ultra-HTHP well X1, the operation design of offshore ultra-HTHP MPD was analyzed from three aspects, i.e., bottom hole ECD, operation parameters and emergency well control. Practical application shows that the system can be used to conduct wellbore dynamic pressure test, pull out of hole (POOH) and connect strings in offshore HTHP wells by controlling back pressure, and can accurately monitor the overflow and lost circulation accidents, so as to reduce the risk and operating costs of HTHP drilling. The research results provide the reference for the popularization and application of this technical system in offshore HPHT blocks and deepwater HTHP blocks.