Design And Study On Down-hole Twin-screw Multiphase Pump

With unceasing explotation of petroleum resources, most oil-gas fileds in our country has already entered the mid or late stage. Mechanical equipments have become the main artificial lift equipments in each oil field. Meanwhile, there come more and more heavy oil wells, deep and low output oil wells, high GOR oil wells and marginal oil wells that make conventional artificial lift equipments impossible. Through the research of this paper, we have developed a new down-hole twin-screw oil-gas multiphase pump that can be used in the harsh oil wells above.First, the design principle of profile for twin-screw pump was proposed briefly in this article, and the composition of the initial profile for twin-screw pump rotor was analyzed emphatically. The coordinate transformation and enveloping principle were used to deduce the conjugate profile of the initial. The equation of the conjugate profile and the meshing relations between the profiles of the initial and the conjugate were obtained. With the analysis to mashing characteristics of the twin-screw pump rotors, the helicoids equations of screw rotors were obtained as well as the equations of the mash-lines, and the equations of the instantaneous touch-lines for the twin-screw pump rotors were deduced by the equations of the mash-lines.Second, the working theory and boostering principle of the twin-screw pump was analyzed in this paper, and the pressure distribution in the pump was abtained. The open area and theoretic displacement of the pump which designed by the new profile were calculated. The slip and backflow in the gaps and clearances of the pump was analyzed emphatically. The pathes and reasons of slip and backflow were pointed out. Meanwhile, the slip and backflow in all kinds of pathes were calculated by fluid mechanics theory. The actual displacement, volume efficiency and effective power of the pump were calculated.Third, three Structural design plans of the down-hole twin-screw pump were discussed in this paper. The paper used the latter two to design the pumps after analyzing pros and cons of each plan. The concrete implementation ways of the pump were given and the auxiliary parts of the pump were designed. With the finite element software, the structural dynamics analysis and the steady-state temperature field analysis to the three dimensional screw rotors were carried out. The axial and the radial direction distortion of the screw rotors in all conditions were abtained and the contrastive analysis to the results of each condition were made.Last, the paper gave the methods to calculate wellbore pressure in all kinds of flow patterns. Taking the pump's export as the solution spot, the macth design for the pressure of the down-hole twin-screw pump was carried on using method of nodal analysis.