Research On Wear Mechanics Between Rod String And Oil Pipe In Vertical Beam Pumping Well

The rod string’s break-off and the leak of the oil pipe caused by eccentric wearbetween rod string and oil pipe have become main reasons to affect pump inspection. Theeccentric wear not only directly causes part rod suckers and oil pipes break and increasesthe costs of the pump inspection, but indirect effects on the oil production which can leadto huge economy loss. Currently, experts and scholars have reached a consensus aboutwear mechanism of rod string and tubing in vertical well that the rod string’s buckling isthe root cause of the eccentric wear, and local initial bending can aggravate this wear trend.In the paper, we will study the calculation methods of the rod string’s environmental loads,rod string’s axial critical buckling pressure and the calculation methods of the contactpressure between rod string and oil pipe. The findings with practical significance of thispaper will be a theoretical foundation to further study the degree of eccentric wearbetween rod string and oil pipe and meanwhile.The main studying contents of this paper can be divided into the following severalaspects.Firstly, considering the comprehensive effect of rod string’s axial distributed pressure,bottom concentrated pressure and couplings’axial concentrated pressure, a model for rodstring’s mechanical analysis in vertical well is established. Taking the influences of theproduced fluid on the friction between rod string and oil liquid, the correspondingcalculation model between them is put forward.Secondly, taking the influences of the elastic stiffness matrix and the geometricstiffness matrix on total stiffness matrix into consideration, a space beam elementsimulation model for rod string’s deformation analysis is proposed. Based on the totalstiffness matrix, a finite element simulation model for rod string’s critical axial bucklingforce and the corresponding numerical algorithm are both founded.Thirdly, according to the spiral buckling configurations, the algorithmic methods for thecontact pressure between rod string and oil pipe, the form parameter of spiral-shaped partand the spatial form of the transition part are given respectively. Meanwhile, thecomputation model for calculating spiral-shaped part’s starting points and ending point isbuilt. The forecast method of rod string’s eccentric wear area is established on the basis ofabove model.At last, by virtue of the Visual Basic 6.0, we develop the mechanical simulation software of the wear of rod string and oil pipe in vertical well. This software can realizerod string’s environmental loads analysis, the calculation of the critical buckling axialpressure and the forecast of the wearing part.