Compared with the conventional surface conductor, the diameter of the suction bucket foundation is generally greater than 6 meters and the length is about 10 meters, which could bring less disturbance of shallow soil during installation and improve the load-bearing characteristics of the subsea wellhead. Theoretical model of the process of suction bucket foundation and bearing capacity calculation method is established, and the influence of diameter and length of the suction bucket on wellhead stability is studied by using the method of combination of simulation experiment and numerical analysis to compared with the surface conductor foundation. The results show that large diameter is mainly helpful to reduce the lateral displacement of subsea wellhead and improve the bending moment performance and vertical bearing capacity of the foundation can be significantly increased by increasing the length of the suction bucket. The large diameter will significantly increase the manufacturing cost and installation cost, with the increase of bucket length, it is difficult for the bucket to install due to the increase of soil resistance. Therefore, it is necessary to design the size of the bucket reasonably in combination with the load-bearing characteristics of subsea wellhead and the properties of shallow soil.
Oil and gas well construction in deep water with suction bucket foundation is the first practice in Norway (Trond Sivertsen et al., 2011). In 2020, the suction bucket foundation is successfully used in the ‘Shen-hu’ area of the South China Sea for the second trial production of hydrates, which combined shallow deflection and dynamic guidance technology, and achieved a breakthrough of 28700 m3/d and lasts for 30 days, (Ye et al., 2020). The application of suction bucket foundation ensures the stability of the upper formation of hydrate siltstone reservoir.
The first suction pile-based jacket platform was launched in 1989 and successfully installed in Norway in 1994 (Morten Baerheim et al., 1995). In 1994, China applied a suction anchor to locate oil tankers in the Bohai Sea for the first time, and installed the double-tube suction anti-slide pile for the "Self-improvement" platform successfully in 1995 (Xu et al., 1995). In 2012, the suction pile underwater foundation plate was successfully installed in the South China Sea, which became the practical basis for the establishment of suction bucket foundation for deep water subsea wellhead (Gu et al., 2014). At present, the design of a suction bucket foundation for offshore deep water well construction is in its infancy, lacking theoretical guidance. To ensure the successful practice of the second round of hydrate production test in China, the diameter of the suction pile is 6.5 m, the penetration depth is 12 m, and the foundation weight of the suction pile is 96 tons. This design is considered by experts to be relatively conservative. It is necessary to continuously carry out theoretical and practical analysis to master the optimization design method of the suction bucket foundation. Reasonable design of the structural size according to the characteristics of formation parameters and wellhead load requirements is the key to the safe and efficient application of suction bucket foundation.
