Study On Preventing Eccentric Attrition Between The Sucker Rod And Tubing In 3D Wellbore

In recent years, the number of eccentric attrition oil well is large in domestic giant oilfield, and the eccentric attrition between the sucker rod and tubing becomes one of the factors which affect pump inspection operation. There are many reasons which affect eccentric attrition, for example, crooked drilling hole, buckling of the sucker rod, high water content, produced fluid with corrosiveness, rod string vibration and so on. No matter controlled directional well or straight well, the well courses are all 3D curves. The stress and deformation of the sucker rod string in oil well present 3D features, therefore accurate understanding of 3D force state is of great significance to reduce accidents and the cost of development. Studying the sucker rod string buckling in 3D wellbore can provide theoretical basis for effectively solving eccentric attrition. The sucker rod force model in 3D wellbore is established through theoretical analysis. The buckling differential equations and contact force equations of the sucker rod string suffered gravity, buoyancy and pressure at both ends in vertical well, slant hole, crooked hole are fetched by means of static balance. The equations fetched are all fourth-order nonlinear differential equations. The two critical loads of the differential equations of the sucker rod in different wellbore are computed using analytical method. The two critical loads are sinusoidal and helix buckling critical loads of sucker rod. The deformation laws of sucker rod in different wellbore and critical conditions of eccentric attrition are obtained. The sucker rod design method and designation adopting weight rod based on the 3D wellbore are proposed. The revised method is based on actual force and deformation, so it is more reasonable.