Study on the marine environment limiting conditions of deepwater drilling for natural gas hydrate

Abstract

Natural gas hydrate (NGH) is a kind of clean energy which has attracted more and more attention. At present, deepwater drilling engineering is an effective way to develop the NGH in deepwater areas. Ensuring the safe and efficient deepwater drilling engineering is the necessity for exploitation of the NGH resources. If the marine environment is particularly harsh, deepwater drilling operations could be suspended, which will affect the process of NGH development. Normally, the operation safety of the drilling system, including the drilling riser, subsea wellhead and conductor, is the limiting factor of the marine environment. Therefore, it is important to study the mechanics of the drilling system for accurate evaluation the risk of NGH development. In this paper, in order to obtain the marine environment limiting conditions of deepwater drilling operations, the mechanical model of the drilling system is established through taking the drilling riser -subsea wellhead-conductor as a whole research object. The top boundary condition of the conductor is determined by the mechanical response of the drilling riser subjected to marine environmental load, and the interaction between the conductor and the soil is described by the P-y model. In addition, the correctness and accuracy of the model is verified. Then, parameter sensitivity analysis is carried out to present a comprehensive influence of the marine environment on the mechanical behavior of the drilling system. Finally, the marine environment limiting conditions of deepwater drilling engineering for NGH are obtained. This study has guiding significance for the safety of deepwater drilling for NGH development.