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Improving the Efficiency of Curved Wells’ Operation by Means of Progressive Cavity Pumps

This paper proposes a solution to the problem of improving the reliability of the operation of progressive cavity pump units in deviated and directional wells. High dogleg severity significantly contributes to rod breakage; rods often break close to the “elbows” with a dogleg severity of 2 deg/10 m or higher. Statistical analyses were used to identify the frequency of failures and their impact on the reliability of a PCP unit. The design layout and mathematical model for pump rods’ torsional vibrations in the curved section of a wellbore were developed. A simulation of the curved section was performed. This article provides the basic formulas needed to design a rotating rod string using two reduced discs. The creation of an additional crooked section resulted in multiple reductions in the “resonant” rotational speed and rigidity in the mathematical model. Determining the moment of inertia of the reduced discs’ mass made it possible to determine the sucker-rod string’s stiffness, the circular rotation frequency, and the number of sucker-rod revolutions under resonance. The number of reduced discs on the sucker-rod string depends on the curvature pattern. In summary, a centralizer for a rotating string was designed to reduce the vibration and shock effects of rods on the tubing.To get more news about bryson pump, you can visit brysonpump.com official website.

Since 2003, long-term experience with the operation of wells using progressive cavity pumping units (PCPUs) driven by a rotating rod string has shown that screw pumps are one of the most effective means for artificial lifting of heavy oils under conditions of low reservoir productivity rates and high gas content at high saturation pressure [1,2,3,4,5,6,7]. The author of [1] provides a study in which a simplified flow model of a PCP is used to control the PCP system and to undertake quick calculations of flow rates. The study presented in [2] focuses on evaluating the effects of the different variables (such as the fraction of gas voids, frequency of rotation, and pressure drop) on the performance of a PCP with two-phase flow. One of the first models used to simulate and analyze PCP performance was that proposed by Belcher in [3]: it was named the “infinite parallel plate” and simulated the slip effect as that of a convergent–divergent bearing. Models are being developed that combine an analytical model to predict the theoretical performance of a pump with a slippage model [4]. Other studies [5,6,7,8,9,10] have focused on studying the effect of the rotor movement on the sealings of stators for various speeds and pressures and on the improvement of pump design.
The simplicity of the PCP design is associated with the absence of valves and complex junctions, thereby significantly reducing hydraulic losses. With a higher viscosity value, fewer crossflows occur through the sealing lines of the elastomer–rotor couple; therefore, the viscosity does not have a significant impact on the screw pump’s delivery rate.
The opposite situation is observed with the other methods of operation (sucker-rod pump, electric submergible pump (ESP), diaphragm pump, etc.). The average delivery rate of the sucker-rod pumping unit is 0.35 at a viscosity of 300 mPa·s, whereas for the PCP unit this indicator equals 0.9 ÷ 0.95. The simplicity of operation makes it possible to reduce operating costs and, thus, the cost of oil production.
It is essential to consider downhole conditions for the efficient operation of downhole equipment. Optimization of PCP wear can be achieved through the geometry of the pump, proper selection of stator elastomers and wear-resistant rotor coatings, and correct selection of the pump size for a specific application [11,12,13,14,15,16,17].
Despite the significant amount of research on the development and optimization of PCP design for well conditions, the operation of wells with PCP is associated with a shortage of effective technical means to prevent or significantly reduce complications in the operation of sucker-rod pumps, particularly in wells with high dogleg severity, which leads to reductions in equipment operating times and in the efficiency of well fluid extraction [18,19].
This is why the development of new technical means for PCP-operated wells is an urgent task and the focus of the present study.
The novelty of this research is the new method developed for modeling the motion of a sucker-rod string during the operation of curved and directional wells. The mathematical model of rod motion elaborated, involving a reduced disc in the curved section of the well, makes it possible to detect hazardous resonance phenomenon. When operating crooked wells, the sucker-rod string takes the shape of a helix or a sine wave of varying pitch. For wells with a number of severe dogleg sections, the frequencies of the forced and natural oscillations of the sucker-rod string may coincide, leading to the increased amplitude of the oscillations and vibration of the sucker-rod string. We developed a new centralizer with the friction of mating surfaces in order to increase the mean time between failures (MTBF) in PCPs.