Influence of Floating Platform-Drilling Riser-Blowout Preventer System on the Dynamic Characteristics of Subsea Wellhead in Drilling

The subsea wellhead is a key equipment connecting the drilling riser and wellbore in a reservoir formation. During deepwater drilling, the motion of the floating platform and wave-current load will cause complex dynamic mechanical behavior on the drilling riser. The dynamic load will be transmitted to the subsea wellhead through the blowout preventer (BOP), which will generate dynamic responses such as bending moment and stress on the subsea wellhead. If the response is too large, the safety of subsea wellhead will be significantly influenced. Therefore, it is important to study the influence of floating platform-drilling riser-BOP system on the dynamic response of the subsea wellhead. In this paper, the lateral vibration of the riser and the rigid connection between the BOP and subsea wellhead under the influence of the floating platform motion was studied. A dynamic analysis model of the floating platform-drilling riser-BOP-subsea wellhead system has been established. And the time history response of the bending moment and stress on subsea wellhead have been simulated. Based on the study, the influence of wave height, wave period, sludge height of subsea wellhead, rotational stiffness of lower flexible joint and wall thickness of conductor on the dynamic characteristics on subsea wellhead have been evaluated and discussed. The analysis results show that the wave period and wave height are the most important factors affecting the dynamic characteristics on subsea wellhead. The rotational stiffness of the lower flexible joint, the sludge height and the wall thickness of the conductor are secondary factors. With the increase of wave height and sludge height, the bending moment and stress increase. However, the bending moment and stress will decrease with the increase of wave period, rotational stiffness of lower flexible joint and the wall thickness of conductor. This study provides a useful reference value for safety control of subsea wellhead in deepwater drilling.