Risk Analysis of Deepwater Horizontal Christmas Tree in Operating Mode
Deepwater oil and gas production requires highly reliable Christmas tree systems.China has devel-oped its first deepwater horizontal Christmas tree,and it is important to ensure this Christmas tree's safety in oper-ating mode.In this paper,an improved hazard and operability(HAZOP)study method was established.Based on the improved probability and severity classification and risk matrix,risk assessment was conducted for three pro-duction nodes(oil and gas production process,chemical injection process,and underwater control system power/communication process).Thus,36 moderate risk points in the operating mode were identified,and corresponding measures were proposed.Through numerical simulation,a mechanical model of the subsea christmas tree-wellhead system was established to analyze the risks(e.g.current load,earthquake,and corrosion)for the system in oper-ating mode.The results show that,in various operating modes,the subsea christmas tree exhibits the maximum stress below 20 MPa and the maximum bending moment below 0.3 MN·m,meeting the safety requirements.However,under the once-in-a-century ocean current after corrosion and earthquake loads greater than 6.5,the system has the maximum bending moment exceeding the allowable value in extreme environment,leading to uncer-tain safety.The research results provide guidance for application of China's first subsea christmas tree in safety manner during operation.
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