Mechanism Analysis of the Regular Pipe Sticking in Extended-Reach Drilling in the Eastern South China Sea

: In the drilling process of extended-reach wells in the eastern South China Sea, the problem of regular pipe sticking is quite prominent. In order to effectively control it, this paper studies the mechanism of regular pipe sticking. It is thought that there are two main reasons: (1) A large number of open hole keyways are formed because connectors grind cuttings bed and wellbore; (2) Serious local cuttings accumulation at the connectors because of axial motion. Based on the above analysis, the mechanical resistance coefficient is introduced to characterize the local resistance of connectors. In this way, an amended drag & torque model is built. The case study shows that the local resistance and additional torque of each connector are about 360 N and 25 N·m during backreaming, and 350 N and 21 N·m while drilling. Furthermore, the mechanical resistance coefficient increases with the increase of cuttings bed thickness and the decrease of formation strength. 1. INTRODUCTION In the 1920s, the United States first used extended-reach wells to develop offshore oil and gas fields, which indicated that the directional drilling technology was developed to a new level (Gao, 2018). At present, extended-reach well has become the key technology for developing complex oil and gas resources in ocean, beach, lake, etc (Gao, 2019). Since the first extended-reach well was drilled in 1997, more than 70 extended-reach wells have been drilled in the eastern South China Sea, which made important contributions to the effective development of oil and gas resources (Shi, 2008; Gao, 2009). However, serious regular pipe sticking caused huge economic and time losses. Fig. 1 shows its typical performance. During the drilling process, pipe sticking occurs frequently and usually takes a single drill pipe as a period, but the circulation of drilling fluid and the rotation of drill pipe string are not suffocated. According to statistics, it takes about 0.5~4 hours to deal with a stuck point, and sidetracking is even required in some severe cases. In general, about 70% of the lost time was related to pipe sticking (Alshaikh, 2018).