Risk Assessment Of Well Control While Gas Cut In Deepwater Drilling

Well control is one of the key factors for safe drilling in deepwater drilling particularly in high pressure gas reservoir drilling.It is very important to accurately knowledge wellbore pressure change,variation of gas rises and its volume,law of wellhead over flow growth during drilling and killing process,which due to gas cut.It is very important to timely appraise risk and its intensity at different formation and working conditions,which aims to build up a reasonable risk prevention and well control measures.On the basis of systemsly research on calculation methods and achievements of well temperature,pressure and risk assessment,the thesis aims to evaluate risk in well control while gas cut in deepwater drilling.By theoretical analysis,the author establishes a model of well temperature and pressure,and analyzes the laws of bottomhole pressure,pit gain,overflow time.The author studys the characteristics of casing pressure under different killing conditions and parameters.Based on wellhead pressure capability,casing internal pressure capability and formation fracture pressure conditions,the author establishes a method of risk assessment including three levels "safe,relative danger and danger".Applying the drilling data of well Eastern South C hina Sea NH3-2 to well control risk analysis.The results show that formation permeability,bottomhole pressure,overflow discovery time,pit gain are the main factors which affect the well control difficulty.For NH3-2 well,safe area of overflow lie within 0.6m3,relative danger area lie between 0.6m3 to 8.4m3,and danger area exceeds 8.4m3.The development provide the ideas to predict difficulty of well control,overflow deadline and killing measures in deepwater drilling.