Risk Assessment of Anchor Dragging for Deepwater Semi-submersible Drilling Platform Mooring System

Risk assessment of anchor dragging for deepwater semi-submersible drilling platform mooring systems is of great significance for ensuring offshore oil and gas development safety. This study addresses the mooring system failure of deepwater semi-submersible drilling platforms under extreme sea conditions and establishes a coupled hydrodynamic analysis model based on ANSYS-AQWA. The research first derives the catenary equation for multi-component mooring lines without elasticity, establishes an anchor dragging mechanical model including anchor holding force and chain retaining force, and proposes an anchor dragging judgment criterion based on tension comparison. Taking the A3 platform as the research object and combining with environmental parameters of the South China Sea, the platform drift and anchor chain tension responses under operating and extreme conditions are analyzed. The Weibull three-parameter extreme value statistical model is used to extrapolate environmental load extremes under different return periods. The results show that under 1379-year return period environmental loads, the safety factors of anchor chains 2# and 3# are below the minimum value of 1.2 required by API specifications, indicating anchor dragging risk with an occurrence probability of 0.989 × 10−6 per year. This study provides theoretical support for risk management and emergency response of mooring systems in deep water drilling operations, and has important engineering application value for improving the safety and reliability of deepwater semi-submersible platforms.