| Screw pump come out in this century. By 2001, the screw pump well in use is about 50,000 in the world, among which 2000 are in Canada, and the others distribute in the other oil field of the world. In China, the screw pump was introduced into in the 1980s, and was tested in the oil field of Daqing and Liaohe successively. The screw pump oil extraction system is mainly sorted surface driving PCP and ESPCP, and the surface driving PCP is mainly used in the domestic oil field. Lately, the oil extraction technique is gradually matured, and every technique index is advanced, especially the life span of the screw rod is prolonged and can meet the request. But along with the spread of the oil extraction technique by driving the big drainage screw pump, especially the usage for the polymer driving well and directional well in Daqing oil field, the problem of sucker rod rapture and dropout is more and more serious. According to the statistic, the screw pump well in the No.1 oil extraction plant was examined and repaired for 33 times, among which sucker rod raptured for 16 times, accounting for 48.5% of the total times. Therefore, the rapture and dropout of the sucker rod of screw pump has been the main problem to restrict the production of screw pumps and has affected the father application. Therefore, on the basis of sucker rod statics analysis, considering the influence of centrifugal force, sucker rod shake, lateral force produced by sucker rod contacts the pipe after its distortion and friction moment of torsion, sucker rod transient nonlinearity finite element model is set up and analysis qualitatively the mechanism forming the deviating-fraction of sucker rod and rapture and dropout. It also analysis quantitatively the collocation reasonably of the guide apparatus and centralizer of directional well screw pump sucker rod to achieve the goal of reducing deviation-fraction and prolong the cycle of repair the pump.At first, the force analysis to the sucker rod is made and the moment of resistance and axial force is deduced. This paper also analyzes qualitatively the mechanism of screw pump sucker rod rapture and calculates quantitatively some effect factors. By the calculation, the primal fault of the sucker rod, the libration of the sucker rod and the centrifugal force are the main cause of sucker rod deviating-fraction.On the basis of sucker rod force analysis, the finite element analyze model is set up by predigest boundary condition. Because when calculated by finite element method to the sucker rod it is involved the problem of geometric nonlinearity and contact nonlinearity, the sucker rod will be divided into many "space girder unit" to solve. Momentum theorem is detruded by the finite distortion theorem. According contact nonlinear theorem, deducing kinematics condition and contact continuum condition. Combining geometric nonlinearity of rod distortion, state nonlinearity of contact between the rod and the pipe and dynamics mechanism, carrying out the analysis and calculation to the screw pump rod and directional well screw pump rod by the ANSYS software.When calculate to the straight well screw pump rod, it is demanded to fix centralizer in the position that formed lateral distortion and enduring bigger contact force to weaken the libration and lateral distortion. The reasonably position will be gained by the calculation result. For straight well screw pump rod, fix a centralizer every three rod will meet the demand. This paper also discussed the influence of rotating speed and sinking speed. Along with reducing rotating speed, the biggest lateral displacement of the sucker rod and the contact force diminishing gradually; Along with reducing sinking speed, the biggest lateral distortion and contact force increasing gradually.Apply calculation software, and do quantitative analysis for directional well screw pump rod string. Take three practical producing wells for instance , there are two conditions which have been analysed for a deflecting point , steadiness bearing angle and some deflecting points , and respectively offer reasonable disposal rule of centralizer and guide apparatus to aim at the two conditions . According to the designed rule , carry into nine wells at scene, at present these wells work steadily, the longest time of steady work is beyonda year , the shortest time of steady work has reached three months . But the well only works steadily within seventy-eight days which isn't designed by this rule . Which also proves the correctness and reasonableness of this rule.The rod string instantaneous state finite element method model established in this article can describe basically the state of the rod string practical movement and pressed distortion , therefore it is significative for scene by calculating and analysing for the model. And it can be known from practical application , can reduce deflectional abrasion if apply the calculation result of this article , prevent the pipe from rupturing , prolong period of maintenance pump. |
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