Research On The Risk Assessment And Control For The Gas Hydrate Drilling

Given the increasing depletion of oil and gas resources,gas hydrates as the most promising unconventional development of new energy sources in 21 st century has become the world's focus attention.Unlike the conventional oil and gas drilling,hydrate formation are effected by the temperature,pressure,composition of pore water and gas supply four factors,having a normal temperature and pressure instability easy decomposition characteristics.It would not only result in wellbore instability,drilling fluid rheology deterioration,well control and other issues,but also equipment damage,huge casualties or major environmental disaster.Based on the risk assessment and configuration selection for the key well control system in gas hydrate drilling,the study is conducted to improve control ability of risk and efficiency of operation of gas hydrate drilling system.The main research achievements are as follows.(1)Preferably analysis of the gas hydrate drilling technologyBased on the gas hydrate complex deepwater drilling environment and the characteristics of the different stages of operation,the core gas hydrate drilling technical problems are presented and different drilling methods are described including the engineering value.Using AHP-TOPSIS risk assessment,the suitable gas hydrate drilling technology and process program are determined.(2)Risk assessment on gas hydrate drilling process modelA OLGA-based model to predict the transient multiphase flow of gas hydrate drilling is developed and the dynamic risk analysis,the logical relationship between the different degree factors are identified.By Comparion the hydrate phase equilibrium curve,hydrate regenerated area is predicted and the key well control system of hydrate is carried out.Combined fault tree and event tree,pre-constructed hydrate drilling operations,drilling,cementing in three stages Bow-tie model are constructed.(3)Failure risk assessment on the key equipment of gas hydrate drilling well controlThe key equipment of gas hydrate drilling well control BOP system T-P numerical model is analyzed based on simulation soft FLUENT.Meanwhile,transient temperature and pressure variation and the key weaknesses of deepwate BOP system are identified.Moreover,based on the Markov method,critical reliability assessment of BOP system and state transition diagram are determined,the working relationship between the state transition or conversion rates are presented either.(4)Research on the gas hydrate drilling process control key equipment selectionCombined risk assessment results of gas hydrate drilling and hydrate formation time,location,generate quality,optimization gas hydrate inhibitor type and concentration are carried out using OLGA and PVTsim software.By analysised the failure under multi-mode working condition,the study on BOP system Markov reliability and key equipment configuration selection of gas hydrate drilling well control using multiple redundant methods are identified.Moreover,the design structure improvement and optimization are designed to assess the state level.