Sealing Performance Research On The Compression Packer Rubbers

As an important downhole tool,packer is widely used in well completion,water injection,fracturing,acidification,sand control,mechanical production,gas lift and other oil production techniques,while the rationality of the structure design and the reliability of the sealing performance of the packer rubber structure has a decisive effect on the safety and reliability of the packer.The finite element analysis of the sealing performance of the packer rubber is simplified as a plane axisymmetric model,while the plane model and the actual exsit a large error for the structure of air bleed hole and anti-burst spring.Setting-up of the three-dimensional model of the packer rubber with air bleed hole and anti-burst spring structure,optimization of packer rubber structure,and optimization of structure parameters of the rubber is of great significance to improve the sealing performance of packer.Based on the investigation of the present situation of the packer rubber at home and abroad,the paper designed four kinds of packer rubber with the structure of bleed hole and anti-spring.The calculation formula of the contact stress of the rubber cylinder was derived under the condition of ignoring the friction and considering the friction in theory based on the large deformation theory and elastic mechanics theory,with the required set-down loads and contact stress under rated working pressure were calculated.The three dimensional numerical model of the rubber with air bleed hole and anti-burst spring structure was set up,and the parameters of the simplified spring model were modified by the experimental results.Based on the model,the bidirectional sealing performance of the four packer rubber were analyzed,containing the compression distance and the contact stress distribution law under the forward and reverse loads of 65.5KN.The paper designed and manufactured the special test equipment for packer rubber,using electrometric method to measur the contact stress between the rubber cylinder and the casing wall,obtaining the reverse limit damage pressure of four packer rubber under the set-down load of 65.5KN.The limit damage tset shows that the anti-burst spring has a protective effect on the end of the rubber,the peak contact stress of double packer element with air bleed hole was the largest of the four kinds under rated working pressure of 21 MPa,while its lack of end structure leads to most serious damage with end protection device suggested.The double packer element with air bleed hole and triple packer element with anti-burst spring was optimized as preferred structure by comparing the contact stress and effective sealing length of the four kinds of rubber.The research studied the effect of sub-thickness,dip angle,total thickness and height structure parameters of single factor on the contact stress of double rubber seal system with air bleed hole,obtained its optimal range,and completed orthogonal optimization analysis of four factors and three levels combined with orthogonal test theory wieh the interaction of factors considered.In recommended parameter combination,the peak contact stress between rubber and casing were increased by 11%.