Constructing and calculating of multistage sucker rod string according to reduced stress

Causes of failures of sucker-rod pumping units, occ urring on oil-and-gas production enterprises, inclu de breakages and twist-offs of sucker-rods, which are exposed to static and dynami c loads. Failures of equipment take place due to gr eat values of cyclic loads, pressing forces and friction, which occur in well deviation intervals or as a result of wrong selection and con struction of sucker-rod string. Correct equipment selection is one of the direction s f reliability growth of rod strings during opera tion sucker-rod pumping units. Therefore, it is necessary to do strength calculati on in the design of rod string. In this article, ro d string design procedure with differential piston pump NN-2SPxx/xx is regarded. The use of thi s equipment lets reduce reversal load and increase the operational life of this equipment. It is done by design features of the dif f rential piston pump. Calculation of hydraulic load by means of rod diame ter regulating in accordance with operating conditi ons was carried out in this work. Reduced stress in the most strained sucker-ro d, maximum and minimum load in rod hanger centre we re determined and calculated reduced stresses were compared according to strengt h condition. Recommendations for steel grade of suc ker-rods, based on results of reduced stress calculation, were given. Also, fibre glass material for sucker-rods was proposed. The ma terial allows sucker-rod weight decreasing as well as increasing of load and non-co rroding cyclic strength