This paper presents a theoretical method and a finite element method to describe wellhead movement and uncemented casing strength in offshore oil and gas wells.Parameters considered in the theoretical method include o...This paper presents a theoretical method and a finite element method to describe wellhead movement and uncemented casing strength in offshore oil and gas wells.Parameters considered in the theoretical method include operating load during drilling and completion and the temperature field,pressure field and the end effect of pressure during gas production.The finite element method for multistring analysis is developed to simulate random contact between casings.The relevant finite element analysis scheme is also presented according to the actual procedures of drilling,completion and gas production.Finally,field cases are presented and analyzed using the proposed methods.These are four offshore wells in the South China Sea.The calculated wellhead growths during gas production are compared with measured values.The results show that the wellhead subsides during drilling and completion and grows up during gas production.The theoretical and finite element solutions for wellhead growth are in good agreement with measured values and the deviations of calculation are within 10％.The maximum von Mises stress on the uncemented intermediate casing occurs during the running of the oil tube.The maximum von Mises stress on the uncemented production casing,calculated with the theoretical method occurs at removing the blow-out-preventer （BOP） while that calculated with the finite element method occurs at gas production.Finite element solutions for von Mises stress are recommended and the uncemented casings of four wells satisfy strength requirements.展开更多
Subsea development is moving constantly toward simplification,digitalization,and cost-out strategies because the exploration and production of hydrocarbons are moving toward deeper and remote sea water areas.Usage of ...Subsea development is moving constantly toward simplification,digitalization,and cost-out strategies because the exploration and production of hydrocarbons are moving toward deeper and remote sea water areas.Usage of all-electric subsea technology instead of hydraulic technology is growing and will be the future of subsea systems due to the former’s environmental and functional advantages and reduced costs.The benefits of all-electric subsea systems are health,safety,and environment(HSE)and improved reliability,flexibility,and functionality compared with traditional hydraulic-electrical systems.Existing electrohydraulic technology for a typical subsea system,hydraulic and electric actuators,and subsea manifold valves including valve types and selection philosophy have been reviewed in this paper.Some major worldwide oil companies such as Equinor and Schlumberger have successful experiences with subsea electric actuators.Considering the benefits of all-electric technology especially in terms of cost and HSE,as well as successful experiences of two major oil companies,further research in this area is warranted.One of the gaps in existing reviewed literature is the effect of using all-electric actuators for manifold valves.Thus,three main questions related to electric actuator selection,requirement of safety integrity level(SIL),and effect of using electric actuators on manifold valve selection have been addressed and answered.Forty hydraulic actuated manifold valves from nine past subsea projects in different parts of the world,mainly Africa and Australia,have been selected for the analysis of all-electric actuators.Results show that 93%of the valves require spring-return electric actuators,whereas 7%can be operated with conventional electric actuators without any spring.The manifold valves do not require SIL certification because they are not connected to an emergency shut down system.Introducing the electric actuators to the manifold valve will not change the valve selection philosophy.展开更多
基金financial support from the National Key Sci-Tech Major Special Item(No.2011ZX05026-001)Program for Changjiang Scholars and Innovative Research Team in University(IRT1086)
文摘This paper presents a theoretical method and a finite element method to describe wellhead movement and uncemented casing strength in offshore oil and gas wells.Parameters considered in the theoretical method include operating load during drilling and completion and the temperature field,pressure field and the end effect of pressure during gas production.The finite element method for multistring analysis is developed to simulate random contact between casings.The relevant finite element analysis scheme is also presented according to the actual procedures of drilling,completion and gas production.Finally,field cases are presented and analyzed using the proposed methods.These are four offshore wells in the South China Sea.The calculated wellhead growths during gas production are compared with measured values.The results show that the wellhead subsides during drilling and completion and grows up during gas production.The theoretical and finite element solutions for wellhead growth are in good agreement with measured values and the deviations of calculation are within 10％.The maximum von Mises stress on the uncemented intermediate casing occurs during the running of the oil tube.The maximum von Mises stress on the uncemented production casing,calculated with the theoretical method occurs at removing the blow-out-preventer （BOP） while that calculated with the finite element method occurs at gas production.Finite element solutions for von Mises stress are recommended and the uncemented casings of four wells satisfy strength requirements.
文摘Subsea development is moving constantly toward simplification,digitalization,and cost-out strategies because the exploration and production of hydrocarbons are moving toward deeper and remote sea water areas.Usage of all-electric subsea technology instead of hydraulic technology is growing and will be the future of subsea systems due to the former’s environmental and functional advantages and reduced costs.The benefits of all-electric subsea systems are health,safety,and environment(HSE)and improved reliability,flexibility,and functionality compared with traditional hydraulic-electrical systems.Existing electrohydraulic technology for a typical subsea system,hydraulic and electric actuators,and subsea manifold valves including valve types and selection philosophy have been reviewed in this paper.Some major worldwide oil companies such as Equinor and Schlumberger have successful experiences with subsea electric actuators.Considering the benefits of all-electric technology especially in terms of cost and HSE,as well as successful experiences of two major oil companies,further research in this area is warranted.One of the gaps in existing reviewed literature is the effect of using all-electric actuators for manifold valves.Thus,three main questions related to electric actuator selection,requirement of safety integrity level(SIL),and effect of using electric actuators on manifold valve selection have been addressed and answered.Forty hydraulic actuated manifold valves from nine past subsea projects in different parts of the world,mainly Africa and Australia,have been selected for the analysis of all-electric actuators.Results show that 93%of the valves require spring-return electric actuators,whereas 7%can be operated with conventional electric actuators without any spring.The manifold valves do not require SIL certification because they are not connected to an emergency shut down system.Introducing the electric actuators to the manifold valve will not change the valve selection philosophy.
