Study On The Chain Risk And Control Measures For The Deepwater Gas Well Blowout

With the increase of global oil demand and urgent requirement for environmental protection,the Petroleum Industry is gradually looking forward to clean energy,meanwhile the Natural Gas Industry,as a significant component of clean energy,still keeps rapid development trend.Due to the decreasing onshore oil production along with yearly booming production cost,Petroleum Industry will concern the North Sea as important development zone,where huge oil and gas reserves exist.Considering inflammable and explosive properties of natural gas and complexity of ocean geological conditions in the North Sea,drilling and production operations are difficult and of great risk.The study on the chain of the deepwater gas well blowout and risk control measures is conducted to support the natural gas safety drilling in North Sea.On the basis of extensive study on both conventional and unconventional well control methods,as well as the natural gas specificity and current technology development status,hard closing and driller's method were chosen for deepwater natural gas well blowout,following the comparison about strengths and weaknesses from shut-in time,circulation time,operation difficulty and failure probability.Furthermore,based on the process of driller's method,well killing process model was established by OLGA.Then the factors leading to well control failure were figured out by the fault tree analysis,and the dynamic risk analysis of the above factors was developed by introducing the concept of redundancy time to obtain risk ranking eventually.The further study was conducted on gas hydrate plugging,recognized as one of the most important risks of well control.Based on the OLGA model of deepwater gas well control,the paper made a study on the effect of shut-in time,mud flow rate and influence of mud temperature to hydrate formation in wellbore annular and choke line.And gas would be sprayed to the platform and began to diffuse under the condition that deepwater gas well control failed.Thus,BOP closing,fire prevention measures,firefighting device,emergency disconnect system and evacuation escape were set as the safety barriers according to the event tree model of well blowout to study the blowout accident development paths.The paper analyzed the natural gas diffusion by Gexcon FLACS,and studied gas-covered area and flammable volume under different wind directions and velocities.Depending on the gas diffusion analysis,the four stages of fire development,preliminary,developing,flourishing and stationary stage were studied further.And the paper also evaluated the extent of damage of the main devices located in downwind direction,referring to two parameters,temperature and thermal radiation.Combined with the above analysis results,the paper defined original events,trigger events and middle events,established domino model of deepwater gas well blowout evolution route,and put forward control measures of hydrate plugging and fire risks to cut off the routes of accident evolution according to the significant trigger events.From the perspective of hydrate inhibitor mechanism,the efficiency of different hydrate inhibitor was studied by the OLGA model,to determine the most adaptable inhibitor for deepwater gas well control.In addition,the minimum inhibitor concentration was also figured out at the exact point when hydrate didn't form in circulation pipelines.Finally,the specific measures was proposed from safety management,fire alarm and firefighting to control fire.