The Research And Application Of Dynamic Analysis Method Of Sucker Rod Strings In 3D Curved Wellbores

The trajectory of directional or horizontal well, which is called three-dimension (3D) curved well in this thesis, is an irregular spatial curve in petroleum industry. Generally, the mechanical behaviors of sucker rod strings in 3D curved well are significant different from that in conventional vertical well. The differences between them are mainly due to the variation of curvature and torsion of wellbore trajectory. It makes the super-thin rod strings with reciprocating motion in wellbore endure the couplings among axial force, torsion and flexure, and the features of geometrical nonlinearity and contact nonlinearity of rod strings are exhibited. Thus the eccentric wear and the break-off of rod strings are induced indirectly and seriously. When slim hole directional well and heavy oil horizontal well were used, this kind of difference is more obviously. Therefore, the numerical simulation method of rod strings dynamics for conventional vertical well and 2D directional well is not applicable to 3D curved well. In addition, a key science problem has not been solved in the dynamic analysis of rod strings, that is, the axis of rod strings is assumed to coaxial with the borehole, then the eccentric characteristics of rod strings in wellbore can not be described clearly. In order to characterize the dynamic properties and the space configuration of rod strings accurately, and to analyze the effection of the position of centralizers on them, a new method for three dimension mechanical analysis of rod strings is need to be studied.First, with the 3D microelement analysis, the vibration model for sucker rod strings was improved by taking into account the influence of actual well trajectory and the fluid resistance. The finite difference method was used to solve the model with the measured data as boundary condition. Then the dynamic properties of rod strings were analyzed, and the eccentric wear position of rod strings was predicted by this method.Second, to overcome the coaxial assumption used in above finite difference method, a new dynamic model of sucker rod strings was established and solved by using finite element method. This new method can embody the features of geometrical nonlinearity and contact nonlinearity, and the couplings among axial force, lateral deformation and flexure of super-thin rod strings in actual 3D curved wellbores. With the time-domain straggling of the kinetic process for sucker rod strings by the Newmark method, the 3D dynamic finite element equation was circularly solved by using the crunode iterative method for the first time. Therefore, the deformation and load in six orientations for each node could be obtained through treating with the dynamic contact between tube and rod strings by means of a direct constraint procedure. Then the 3D spatial configuration of rod strings in wellbore was described in details. In the meantime, the validity and reliability of the finite element method proposed in this thesis were confirmed by comparing the difference of spatial configuration and load of rod strings with various fixation patterns of centralizer and with or without it.Third, the classical empirical formula can not give an reasonable boundary condition when new unconventional rod pumps with small sizes were used in slim hole directional well. In order to obtain more accurate results, a testing tool for slim hole directional well was developed and then used in two wells, and the measured boundary conditions were obtained for the first time.Forth, with the measured temperature data, the oil viscosity in heavy oil horizontal wells of Kelamayi oil field was investigated, and a resistance model related to variable-viscosity annulus fluid was determined. Then the dynamic features of rod strings in heavy oil horizontal wells were calculated and analyzed.Finally, based on the simulation model and numerical methods presented in this thesis, a simulating program was compiled by using MATLAB language. The program was verified by examples with analytic solution, and the validity and rationality of the finite element method proposed in this thesis were confirmed by comparing the numerical results and the measured data.