The Optimum Design For The Sucker-rod Pumping System Of Ultradeep Well In Halahatang Oil Field

The wells in Tarim Oilfield are generally deep, especially in Halahatang oilfield, where the burial depth is 6650 m to 7500 m, temperature is 151℃ to 170℃, pressure is 75 MPa to 79 MPa and H2 S is as high as 120000 ppm. In the initial stage, the wells could produce by natural flowing, but the duration is short, so it was important to solve the problem of pumping in ultra-deep well after a long time. When the length of sucker rod string increases, the polished rod load and tensional moment increase as well, general beam-pumping system will not meet the need of pumping in ultra-deep well. And, the increase of the load and deformation of the sucker rod string will decrease the efficiency, even make the string break. The reasonable design and use of the sucker rod can not only improve the efficiency of the sucker rod, but also can improve the efficiency of the pumping system and ensure the safety and reliability of the sucker rod.In this paper, the sucker rod in ultra-deep well was taken as the object. With the consideration of the axial pressure, torsional moment, fluid pressure and friction force, the load of the sucker rod, polished rod load, the maximum load and the minimum load of each sucker rod were analyzed. By the energy method and variation principle, the buckling equation of the sucker rod under the pressure and torsional moment was established. The buckling critical loads of the sucker rod in the vertical well were deduced. With the consideration of the real trace of well bore and 3D description of the sucker rod, 3D equilibrium equations of the sucker rod were established. Based on the theory of energy, the sinusoidal buckling critical load and helical buckling critical load of the sucker rod were deduced. To find the minimum weight of the sucker rod, a MATLAB optimization program was developed based on the criteria of equal strength. It was found that the tensile strength of sucker rod was seriously affected by the Goodman coefficients. The bigger of the Goodman coefficients, the longer of the sucker rod, but the safety factor will become smaller. Finally, the procedure of the optimization design of sucker rod was provided and used in Halahatang oilfield successfully.