Research On Cementing Technology And Failure Analysis Of Stage Cementing Collar

As a key component in the process of fractional cementing,the stage cementing collar is an important guarantee for the continuous operation between the first-grade cementing and the second-grade cementing.The fractional cementing technology is mainly used when the cementing amount is too large,the formation fracture pressure coefficient is low,the sealing section is too long,the formation permeability loss is serious,the well depth is too deep,casing too long,and one-time cementing can not meet the requirements of the well.Usually,the graded cement injector operates in a coupled field with complex thermal environment and variable force action.Moreover,there is a certain clearance between the main body of the stage cementing collar and the sliding sleeve.Therefore,its structural rigidity must meet certain requirements.However,the stage cementing collar cannot fully meet the cementing requirements in the actual use process,and various failure phenomena often occur,which seriously affects the construction quality and work cycle,and brings huge economic losses.Based on the actual cementing conditions of an oil well,this paper adopts the method of numerical simulation to study the main reasons for the failure of the stage cementing collar in the actual work.The main research contents are as follows:(1)Taking the cementing process of an oil well as an example,firstly,the well structure of an oil well,the data of the pipe string and the fluid parameters during cementing are described,and the injection-replacement process during the actual cementing is described in detail,and established the fluid mechanics model during the mud flow during the solid well.Summarize the characteristics of cement slurry changes in the process of solid well and the various pressures and resistance generated during the well-solid well.Finally,it was analyzed based on the actual conditions of the well solidarity.The cause of the failure of the stage cementing collar was analyzed.(2)Establish a three-dimensional finite element model according to the stage cementing collar actually used in an oil well,and use ICEM software to divide the grid,and analyze its structure based on the method of thermal-fluid-structure coupling numerical simulation.The distribution of fluid pressure,velocity,and deformation under different cementing conditions is studied,and the influence of structural deformation on failure modes such as the inability to open and close the circulating hole of the stage cementing collar under different conditions is analyzed.(3)Based on the water hammer theory,the CFD numerical simulation method is used to analyze the water hammer pressure generated by the U-tube effect during the cementing process.Use the dynamic grid function in Fluent software to realize the transformation of the boundary to simulate the conditions of water hammer.The influence of the water hammer pressure generated under different pump pressures and different densities on the failure modes such as early opening and early closing of the circulating hole of the stage cementing collar is simulated.(4)The fluid-structure coupling vibration analysis is carried out on the main body of the stage cementing collar,and the effects of the dry mode under the action of air,the wet mode under the action of the additional mass of the fluid,and the mode under the prestress on the natural frequency of the structure are considered.The multi-objective optimization method is used to optimize the stage cementing collar.The most important parameters affecting the structure are selected as design variables,and the minimum deformation and minimum mass are selected as the optimization objectives,so that the deformation of the stage cementing collar is minimized under the same working conditions,reduce the probability of failure,and provide certain theoretical guidance for the actual cementing design.