Risk Assessment And Control Of Major Accidents In Deepwater Drilling Operations

The deepwater drilling operations face huge risk because of the special workingenvironment conditions. Once a major accident happened, it would cause serious effects onthe economy, environment and society. In order to ensure the safety of deepwater drillingoperation, we must carry out the risk assessment of major accidents to find out the risk factorsin deepwater drilling operation, and carry out technology study on risk control and riskprevention to prevent major accidents to happen. The dissertation combined with thesub-topics ‘Study on riser operation management and safety assessment technology indeepwater drilling’ of the ‘12th five year plan’ national science and technology majorprogram ‘Deepwater oil and gas drilling and completion engineering supporting technology’,and the independent innovation scientific research project of china university of petroleum(East China)‘Risk control technology and application foundation research in deepwater oiland gas exploration of The South China Sea’, and the sub-topics ‘Deepwater surface drillingtest risk analysis and control’ of863major project ‘Key technology and equipment study ofdeepwater surface drilling’. The main investigate issues include the deepwater drillingoperations risk assessment, formation and development mechanism of major accidents, safetybarrier technology, the diffusion law of sour natural gas blowout and oil spill, deepwatersurface drilling operation risk control, it provide effective technical support for deepwaterdrilling operation risk assessment and control. The main research results of this paper aresummarized as follows:1Study on risk management system in deepwater drilling operationsA risk management system in deepwater drilling operations, whick mainly includes sixsub systems, risk identification, risk assessment, risk acceptance criteria, risk control, riskmonitoring and risk early warning, is proposed. Each sub system is detailed described. Themajor problems in deepwater drilling operation are analyzed. The main risk factors indeepwater drilling operations include material risk, technology risk and environment risk. Therisk assessment indexs system in deepwater drilling operations is established by geologicalconditions factors, human factors, organizational management factors, environmental factors,structure factors, process technology factors. Based on the AHP method and fuzzy evaluationtheory, a risk assessment model in deepwater drilling is established.2Major accidents risk analysis and safety barrier technology researchMajor incidents and the reasons occurred in offshore drilling operations in recent yearshave been described. A fault tree model is set up to analyze risk factors of blowout accidents.Through the analysis of safety barrier technology, the safety barriers are divided into threeparts, technical barrier, personnel/organizational barrier, operation barrier, and then ananalysis model of safety barrier system is established. Considering the cumulative effects ofrisk factors, a major accident causation model in deepwater drilling operations is proposed. Taking the deepwater horizon disaster as an example, the paper analyzes the major accidentsformation logic relationship and safety barrier system failure model.3Study on simulation of blowout accident of deepwater offshore drilling operationsContraposing the characteristics of the multitudinous equipments and narrow space onthe drilling platform, a geometric modeling method of complex structure is established. Basedon the analysis of atmospheric diffusion conditions and ascertainment of the hazard gasevaluation standards, a numerical simulation model of sour natural gas diffusion is established.The influences on sulfur natural gas diffusion from wind direction and wind velocity aresystematically analyzed, and the transportation and distribution of sour natural gas areobtained. A modeling method of methane combustion and explosion is established to analysethe hazard of the blast wave and radiation. Contraposing the oil pollution of deepwaterblowout, a numerical simulation model of oil diffusion in deepwater is established. Theinfluences on oil diffusion from the current velocity, sea-water buoyancy, and spill volumeare systematically analyzed.4The key equipments reliability analysis in deepwater drilling operationsThe riser system and BOP system are the key equipments in deepwater drillingoperations, and the reliability of the two systems are analysed. The results show that, thecorrosion, abrasion and large platform offset are the main reasons for the failure of the risersystem, and primary control system failure is the main cause for the failure of the BOP system.The mud density dynamic adjusting device is the key equipment of dynamic killing drilling(DKD), and a performance assessment model is set up to analyze the well bore pressure,drilling fluid density, pumping pressure and the other key process parameters, and todetermine whether the DKD equipment is suit for the deepwater drilling operations. Takingthe South China Sea deepwater pilot hole well testing process and the latest DKD device forexample, the reliability of DKD equipment is analyzed.5. Risk accessment and risk control of deepwater surface drilling operationsTaking the deepwater surface drilling operation as an example, the risk accessment andrisk control of deepwater drilling are detailed studied. Based on the risk matrix, HAZOP, andFMEA method, the risk of different drilling technological process and key equipment ofdeepwater surface drilling is studied, and the main risk factors are obtained, and sometargeted risk control measures are proposed. The fuzzy comprehensive evaluation ofdeepwater surface drilling is carried out, and the drilling operations risk rating is obtained.Then focusing on shallow gas accident in deepwater surface drilling, a Bow-tie model ofshallow gas blowout is established, and some safety barriers are proposed for accidentprevention and control.