| Key mechanical problems during deepwater riser-less drilling operation is discussed in this paper, including soil mechanics, static and dynamic analysis of landing string, which based on the analysis of deepwater riser-less drilling processing, operation challenges and risks.As to the problem about the conductor sinking down and limit tensile loading of landing string, simulated experiment about conductor jetting operation is firstly conducted in china, and based on similarity theory, a theoretical model about lateral friction for jetting conductor is established using a large mount of experimental data, which can suitable conditions onsite.As to slip crushing for landing string during deepwater drilling, loading characters of deepwater landing string is analyzed and found that regular Reihold-Spiri model is not suitable for deepwater landing string. Based on analysis of the mechanism of pipe-slip interaction, A new model for calculating slip crushing load is established using thick-walled cylinder theory and beam-column theory, and validated it use examples, The model can be used as a design basis of landing string in deepwater drilling, and also can be used to calculate the string operation window which can provide guidance for emergency treatment, thus to protect the safety of deepwater drilling operations.According to dynamic effect on landing string about marine and drilling unit motion, the drilling unit motion equation, and static and dynamic equations for landing string are established based on rotor floating body theory and slender bar theory, furthermore, dynamic analysis method is established with interactions between landing string and drilling unit under marine environment.Therefore, one set of static and dynamic analysis methods concerning deepwater riser-less drilling operation which taking the consideration of marine environment and drilling unit motion, it can be used to analyze operational window and safety margin for deepwater riser-less drilling, and provide scientific guidance for taking reasonable technical measures. While, a new method and thought is provided for deepwater drilling string mechanic analysis, which has great significant and provide guidance on research of deepwater drilling string mechanic, such as riser.Some meaningful conclusions are obtained by detailed calculation and analysis on the key mechanic problems about the first deepwater wells, LW6-1-1, which is also the first self-operated deepwater wells drilled in china southern sea, which provide well-guidance for taking technical measures onsite, and ensure safety operations. |
