Study On Dynamic Pressure Change And Pipe String Mechanical Behavior In Cementing Process Of Deep Well Or Ultra-Deep Well

This dissertation is funded by 12th Five-year National Science and Technology Major Project-Large Oil and Gas Field and Coalbed Methane Development-"Demonstration Project of Oil and Gas Development in Kuche Foreland Thrust Belt of Tarim Basin"(Project No.:2011ZX05046),as well as Doctoral Scientific Fund of the Ministry of Education(Project No.:20135121110005).This dissertation is focused on KD2 ultra-deep well in an oilfield of Xinjiang.After running casing,three casing fracture accidents happened in the cementing operation,which led to direct economic loss of 150 million RMB.Therefore,this dissertation carries out study on dynamic pressure change in cementing process of deep well or ultra-deep well and mechanical behavior of drillstring in casing or linear cementing process.Besides,the main causes of failure accidents are studied and corresponding control and prevention measures are proposed.The main content and achievements are as follows.(1)For the casing fracture accident of KD2 ultra-deep well,analysis and study on accident cause are carried out based on field data,fluid dynamics model and pipe string mechanics theory.The main research content of pipe string mechanics is proposed in cementing process of deep well or ultra-deep well.(2)Fluid friction model,dynamic pressure calculation model,flowback rate calculation model,fluid acceleration model and impact force calculation model are established,which provides analytical mathematical models for calculation,optimal design and software development of fluid dynamics parameters in cementing process.(3)According to cementing process of KD2 well and fluid dynamics theory,cementing process is divided into continuous fluid process,discontinuous fluid process and continuous fluid process.Fluid dynamic pressure parameters calculation models of original casing structure and simplified casing structure are derived,calculation model for flowback rate of discontinuous fluid is deduced,and calculation model for flowback rate at different time is established.(4)Based on basic theory of U-tube fluid dynamics,several mathematical models are established,including fluid friction model,dynamic pressure calculation model,flowback rate calculation model,fluid acceleration model and impact force calculation model,which provides simple method and reliable means for calculation and optimal design of fluid dynamic pressure parameters in cementing process.(5)According to the liner cementing proposed in this dissertation,the calculation models of pipe strength,deformation and fluid friction are established,and the analytical mathematical model of drill string dynamic friction force and deformation with time is derived.(6)Based on the previously established analytical models,a calculation software with independent intellectual property for fluid dynamic pressure parameters and string deformation is developed.The software has been applied and verified,which provides reliable method for fluid dynamic pressure parameters calculation,cementing parameters optimization and calculation of drill string dynamical friction and deformation in liner cementing operation.