Research On Sealing Performance And Fracture Failure Of Shape Memory Polymer Packer Cartridges

Packers are important downhole tools for sealing annulus,isolating oil and gas,and controlling injection and production.With the increasing scarcity of global oil resources and the increasing difficulty of unconventional energy extraction,traditional packers have gradually been unable to meet the harsh and extreme downhole environment.The packer made of shape memory polymer has the advantages of simple structure,easy processing,high adaptability to the naked eye and controllable temperature,etc.,and can solve many problems existing in mechanical packers.Based on the generalized Maxwell viscoelastic model,a finite element mechanical model of the shape memory polymer packer is established in this paper.Stress relaxation tests were carried out on epoxy-based polymers,and the relaxation modulus curves of the materials at different temperatures were obtained.According to the time-temperature equivalent principle and the WLF equation,the main curve of the material relaxation modulus was drawn.series coefficients to accurately characterize the mechanical properties of polymers.Thermomechanical tests were carried out to obtain the thermal expansion coefficient of the material at different temperatures,and tensile tests were carried out to obtain the fracture energy of the material at different temperatures.The mechanical behavior of the shape memory polymer packer in the process of high temperature precompression,cooling solidification,low temperature unloading,heating recovery,steady state setting and application of working pressure was simulated by finite element,and the distribution law of contact stress and shear stress was summarized.,and analyzed the influence of rubber barrel length,interference,pre-compression,setting temperature and wellbore pressure on sealing performance.Based on the J-integral fracture criterion,the effects of pressure difference,crack length,crack location,rubber tube length and thickness on the fracture failure of the packer were analyzed by using the finite element model.The research results show that: in terms of the sealing performance of the packer,the wellbore pressure has the greatest effect on the contact stress and shear stress of the packer,followed by the length of the rubber barrel and the interference,while the precompression and the setting temperature are the two factors.parameters with less effect.Although high wellbore pressure can generate large contact stress,it will also lead to increased shear stress.Excessive shear stress can easily cause the packer to slip and fail.It can be adjusted by adjusting the rubber barrel length and interference of the packer.To obtain the proper shear stress,the amount of precompression and setting temperature can be considered as secondary considerations when designing the packer structure.In terms of packer fracture failure,the greater the pressure difference,the longer the crack length,and the more likely the packer rubber cylinder to fracture and fail.Cracks at the top of the rubber barrel are more prone to crack propagation.It is recommended to add a protective structure at the top of the rubber barrel to improve the fracture toughness of the crack initiation point.The influence of the length of the rubber barrel and the thickness of the rubber barrel on the J integral is positively correlated.When designing the rubber barrel structure,it is not appropriate to use the packer rubber barrel with too long and too large interference,and the long rubber barrel will make the crack easier.Although the rubber cylinder with too large interference has little effect on crack propagation,it will require a larger amount of pre-deformation,which will easily lead to plastic deformation of the polymer,reduce its shape recovery ability,and affect the reliability of setting.