Performance efficiency of rod units, which are widely used all over the world for artificial oil lifting, depends to a large extent on feasible layout engineering of rod string, performing drive of reciprocal movement from pump motor to sucker-rod plunger. Steel is usually used as a material for production of sucker rod. However, application of steel sucker rods could lead to efficiency decrease due to the increased sucker-rod string total weight and increased pump motor load if increase in the length of rod string is required (due to lower formation pressure and the necessity of deep-laying deposits extraction). Taking into account this facts, electrical centrifugal pump plants are used in all Russian oil fields with deep wells, including stripped wells. Reaching cost-efficient deep well development could be achieved by application of composite pump rods made of fiberglass, which allow to significantly decrease load on pumping outfit and pumping motor thanks to much lower weight, higher strength and corrosion resistance.
The article presents mathematical model of the unit with combined rod string, which includes steel and fiberglass pump rod. Calculations of dynamic distortions and force were conducted during work process of rod unit with steel and combined strings in the well with low-viscous pumped out liquid. The results shows that rod string efficiency increases when pump with small diameter landing depth increases. Areas of resonant vibration response for rod string, which lead to increase of rod string vibration amplitude and effective plunger stripping thanks to coalescence of beam oscillation frequency with self-resonant frequency of rod string, were defined. The simulation showed that the most rational is pre-resonant frequency mode when reciprocating speed was almost as high as (but not lower than) resonant frequency. This operation mode makes it possible not only to reach effective plunger stripping thanks to the growth of dynamic distortions, but also to decrease the level of maximum and presented loads in rod string and loads on sucker- rod pump motor thanks to significant decrease of rod string weight.
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