Nonlinear Simulation Of Expander Packer Under High Temperature And High Pressure Environment

With the increasing difficulty of oil production,unconventional oil and gas resources were the main form,and in unconventional oil and gas production,multi-stage fracturing technology was the key,mainly relying on the packer to achieve the separation,sealing performance and safety of the packer was a key factor in fracturing operation.In this paper,Aiming at the working condition of expansion packer under high temperature and high pressure environment,established the expansion packer mechanical model,the remeshing method was used to describe the rubber nonlinear flow in the annular clearance,and remeshing before and after the information of grid mapping,solved the packer finite element equation matrix singular problem.The displacement of packer rubber,shear stress of matrix and contact pressure between rubber cylinder and casing were simulated under different fracturing pump pressure,different well temperature,different annulus clearance and different card distance.The results were as follows: the fracturing pump pressure was between 30 MPa and80 MPa,no occurs axial movement of the rubber cylinder,and the shear stress of the rubber matrix and contact pressure increased with the increased of the fracturing pump pressure.The fracturing pump pressure was greater than 50 MPa,the rubber cylinder was prone to shear and tear,led to failure of the matrix;The well temperature was between 25 ℃ and 175 ℃.With the increased of the well temperature.the shear stress of the matrix increased.The well temperature was greater than 85 ℃,the matrix was prone to shear tearing;The annulus gap of 2.5 mm～9.5mm.With the increased of clearance the shear stress of rubber tube matrix increased,and the contact pressure between rubber tube and casing decreased.The reasonable clearance was 2.5mm ～ 5.5 mm;The card distance was 10 m～70 m.With the increased of card distance the shear stress and contact pressure show a trend of nonlinear increased or decreased,the reasonable card distance was 30 m.It can be concluded from the mesh deformation that the nonlinear flow of rubber in the annulus gap was the fundamental reason for the increased of shear stress value of rubber matrix and the decreased of contact pressure value between rubber and casing.In conclusion,with the increased of fracturing pump pressure,well temperature and annular clearance in fracturing operations,the packer rubber barrel was more prone to shear and tear failure.The sealing effect of the packer was also reduced,resulting in fracturing operation failure.Based on the above evaluation results,an expanded packer filled in nylon 66 cord in rubber matrix was proposed in this paper.The critical failure energy of the interface between nylon 66 cord and rubber matrix was obtained by single pulling out experiment.The CZM(Cohesive Zone Model)was used to describe the bonding state between nylon cord and rubber matrix.The failure criterion of adhesive failure of composite interface between nylon 66 cord and rubber matrix was established.The mechanical properties of nylon 66 cord packer rubber cartridge under different pressures and well temperatures were systematically analyzed.The results were as follows: the fracturing pump pressure was 50 MPa～80 MPa,the shear stress of the rubber matrix was less than the allowable shear stress,and there was no shear tear in the matrix.Therefore,nylon 66 cord was filled in the rubber,which can effectively protect the matrix.However,the fracturing pump pressure was greater than or equal to 80 MPa,the failure of the interface between the nylon 66 cord and the matrix was greater than the critical failure energy,resulting in the failure of the interface between the cord and the matrix;The well temperature ranges from 25 ℃ to 175 ℃.With the increased of temperature the shear stress of the matrix and the composite interface of the rubber cylinder increased.But the shear stress of the matrix was less than the allowable shear stress,and the failure energy of the interface was less than the critical failure energy.Therefore,there was no debonding between the cord interface of the rubber cylinder and the matrix,the sealing state was good.As a result,nylon 66 cord expansion packers can operate under higher pressure and well temperature environments.The research results of this paper can provide theoretical guidance for further exploring the performance of the cord expansion packer cartridge.