Structure Design And Material Research Of Dissolvable Metal Bridge Plug

Domestic and foreign oil and gas exploration has shifted the focus from conventional oil and gas resources to unconventional oil and gas resources,and segmental fracturing of horizontal wells technology can effectively improve the productivity of unconventional oil and gas fields.Dissolvable bridge plug is a new technology in the field of staged fracturing technology for horizontal wells,and it can be dissolved in the flowback liquid after fracturing operation,avoiding the problems caused by the complexity of traditional bridge plug unsealing process.Therefore,the research and development of high-performance dissolvable materials and dissolvable bridge plugs is vital for the exploration of unconventional oil and gas resources.In this work,the materials and structures of dissolvable bridge plug were researched,and the main research contents were as follows:In terms of dissolvable materials,dissolvable magnesium alloys with different contents of Al were prepared by casting,and the metallurgical microscope,SEM,XRD,EDS,micro-hardness tester,compression tester,electrochemical workstation and other instruments were applied to research the microstructure,phase composition,mechanical property and solubility property of dissolvable magnesium alloys.The results showed that the main phases of dissolvable magnesium alloys were composed ofα-Mg,β-Mg₁₇Al₁₂ and Al₅Mg₁₁Zn₄,meanwhile,as the content of Al increased,the amount ofβphase of dissolvable magnesium alloys increased,and the distribution pattern transformed from diffuse block and discontinuous strip to continuous mesh.With the increase of Al content,the Vickers hardness of dissolvable magnesium alloys increased,the compressive strength increased and then decreased,and the plasticity decreased.The maximum compressive strength of the dissolvable magnesium alloy reached 383.6 MPa when the content of Al was 20 wt.%.The fracture mechanism was the brittle fracture of cleavage fracture.The dissolution rate of dissolvable magnesium alloys increased first and then decreases with the increase of Al content.Dissolvable magnesium alloys could realize the dissolution rate of 33.55 mg·h^-1·cm^-2 in the KCl solution of 3 wt.%at 80℃when the content of Al was 20 wt.%,and the dissolution rate could be promoted by elevating temperature and increasing the concentration of Cl^-.In the aspect of dissolvable bridge plug structure,aiming at the problems of complex structure of conventional dissolvable bridge plug and incomplete degradation of rubber seals,the dissolvable metal bridge plug was designed according to related principles,the setting tool applicable for dissolvable metal bridge plugs was selected and the detailed structural design and strength analysis of the main parts of the bridge plug was carried out.Besides,the finite element model of the bridge plug sealing mechanism during setting process was established to investigate the influence of main structural parameters of the metal sealing ring on its equivalent stress and contact stress with other parts.The optimal structural parameter combination of the metal sealing ring was obtained through orthogonal analysis method with the maximum contact stress as the evaluation standard as follows:the inner cone angle was 10.5°,the radius of ring convexity was 9 mm and the distance between the ring convexity and the front face of the sealing ring was 11 mm.The effect of setting distance on the setting force,equivalent force and contact stress of the metal sealing ring was also studied.In the meantime,the finite element model of the bridge plug anchor mechanism was established to analyze the influences of the main structural parameters of the slip on the stress distribution of it,the maximum equivalent stress of the casing and the contact stress between the slip and the casing.With the objectives of improving the stress condition of the slip,reducing the damage of the slip to the casing and improving the contact performance between the casing and the slip,the optimal structural parameters of the slip were selected as follows:the inclination angle of the tooth of the slip was18°,the distance between the first row of groove and the front face of the slip was 15 mm and the angle of the groove axis was 14°.