Casing Mining Research And Application Of The Mechanical Behavior Of Oil Well Sucker Rod String

After 5~1/2" casing pipes having been corrupted and punched, Caiyou Wuchang in Zhongyuan oil field carried out well workover with 4" casing pipes, but it is impossible to pump with big pump and the pump setting depth is limited .Consequently, Caiyou Wuchang directly makes 4" casing pipes as lift pipe string without tubing to pump oil. Field indicates that due to reasonless rod design, the friction between sucker rods and casing pipes is severe, the emergency of collapse and dropout happened frequently, pump check period id short.As one type of tubingless rod pumping technique, Casing production technique produce crude oil directly with casing pipes and sucker rods, which is improvement on conventional rod pumping technique with tubing. Casing production well being the object of research, aimed at the fact of severe friction between sucker rods and casing pipes, on basis of studying deeply the dynamics behavior of sucker rod, the paper established a method of analyzing and designing sucker rod which is suited to casing production well.The paper studied the buckling process of sucker rod in the well bore. After sucker rod transforming from sinusoidal buckling to helical buckling, the connection between rod and casing pipe becomes linear connect from point connect, so the connect force will increase sharply and produces severe friction between rod and casing pipes. And the torque produced by helical buckling makes the sucker rod dropout, and badly shorten the pump inspection period. Consequently, the paper studied deeply helical buckling to provide theoretical basis for friction control.Buckling critical load is related to bending stiffness and linear weight of sucker rod, for directional well, it is related to borehole deviation and radial clearance additionally. Because the radial clearance of casing production well is larger then that of conventional rod pumping well with tubing, the sucker rod in casing production well tends to buckle helically. By establishing and solving helical bucking differential equation, we obtain the calculation models of bending moment, distortion moment and stroke loss, which provide effective method for analyzing buckling behavior of sucker rod in casing production well.Due to the difference between vertical well and directional well, the paper applied different methods to analyzing rod dynamics behavior and designing sucker rod .For vertical well, API RP 11L method is applied, but for directional well, the paper applied a method of calculating upward one by one from pump.Differently based on longitudinal and lateral bending theory and borehole geometry,we obtained the design mode of couplings above and below neutral point.Applying Visual Basic ,the paper make modes of buckling ,load calculating, rod designing , sinker bar and couplings designing to realize on computer. It provides effective means for analyzing sucker rod dynamic behavior and designing rod combination in casing production well.Taking two wells of Caiyou Wuchang in Zhongyuan oil field , as examples ,H12-150 and H7-79, the paper applied the program to calculate rod load s and analyze buckling, what's more, it designed sinker bar with different diameter and corresponding sucker rod combination, finally couplings have being designed.