Risk Evaluation And Control Of Deepwater Subsea Mudlift Drilling System

In the deepsea drilling process of the conventional marine drilling method, a series of well control problems are often encountered. Foreign oil industry established Subsea Mudlift Drilling (referred to as SMD), a kind of the dual-gradient drilling technology. Now Widespread application of SMD technology has been made, risk evaluation and control task is necessary, especially in deep water environments. This paper is sponsored by "subsea mudlift drilling technology"(2008ZX05026-001-12), which is subtopic of"Development of large scale oil&gas field and coalbed gas"National science and technology major special project, and"Fundamental Research on Risk Control Techniques Application for Deepwater Oil and Gas exploitation in South China Sea", to carry out risk assessment and control research of Subsea Mudlift Drilling.Statistical analysis showed that the accident of SMD was mainly cyclic leakage accident, suction hose, and install difficult under bad weather conditions. Using FTA, FMEA and other methods, qualitative risk analysis were made. Quantitative risk assessment was made using AHP method, the results show that: risk factors such as the integrity of the mud return pipeline, suction hose reliability, suction module sealing performance, monitoring and treatment of underground accident took greater weight.With ABAQUS finite element software, 1500m/500m waterdepth mud return line mode were built for the mechanical analysis and VIV fatigue analysis , calculation verified the return pipeline safe and found: the equivalent stress and axial stress diminished with decreasing water depth and reached its maximum at the top support points, stress mutation was found at subsea pump module, the maximum equivalent stress values appeared in the same direction as currents flow and pipeline tilt; top and bottom of MRL showed larger bending moment, fatigue damage mainly concentrated at the top of MRL, overall fatigue damage of MRL is small. SMD safe operation was wrote, risk reduction measures were made from the angle of the key equipment manufacturing, key equipment testing program was proposed. SMD system parameter model under kick/lost accidents was established and simulated. BP neural network model of SMD kick was established, results prove the feasibility of the network. Monitoring technical and response strategies were researched for major accident like kick and lost circulation. In response to a large number of shallow gas release and platform withdrawal, emergency shutdown and quick release system of the mud returnline were studied, and schematic drawing was made using Autocad.