Rod String Research Articles

Analysis and improvement of the design of uninterrupted connection of pump rods

Based on the field data, numerous failures of the downhole equipment of sucker rod pumping units occur, especially of the sucker rod strings. They are subject to corrosion, wear and alternating loads. The stress-strain state of the threaded connection elements is determined by the nature of the distribution of loads along the threads, which is uneven and depends on many factors. Despite this, the development of new designs of sucker rod connections and measures to improve the efficiency of operation and their research is an urgent task. In addition to the threaded connections of the sucker rods, there were a number of threadless designs that were not used in the fields, but they passed certain tests. The article presents these connection designs and discusses their advantages and disadvantages in comparison with standard threaded connections. Simulation modeling of a standard connection of sucker rods made it possible to investigate its stress-strain state and identify hazardous areas (stress concentrators). The stress-strain state of the threaded connection of the sucker rods has been investigated, the design of this connection has been improved and it has been established that, in comparison with the standard threaded connection of the sucker rods, the investigated has certain advantages. It was found that with an increase in the number of protrusions and depressions in a threaded joint, stresses decrease, which are concentrated in dangerous sections and along the contact planes. Convex contact planes also reduce stress, especially at the joint surface. Research has shown that the stresses generated in a threadless sucker rod joint are less than the stresses generated in a standard sucker rod and sleeve joint. Although the difference between these stresses is insignificant, attention should be paid to changing the geometric parameters of the threadless connection of the sucker rods, thereby reducing the maximum stresses.

Sucker rod pump downhole dynamometer card determination based on a novel finite element method

An advanced dynamic finite element model is presented that diagnoses the downhole pump performance of sucker rod pumping systems, applicable for any pumping conditions and equipment used. The results are compared to downhole measurements and other evaluation techniques. Buckling is an undesirable phenomenon occurring in sucker rod pumping. It essentially depends on the plunger load, which is a function of time and typically not measured but evaluated by diagnostic tools. Existing diagnostic tools exhibit specific limitations that reduce their applicability and output quality. This paper introduces a diagnostic tool, which can predict the rod string's stress field and its movement not only at the pump plunger but all along the rod string. Moreover, this tool can account for the interaction between rod guides and tubing as well as rod string and tubing. To this end, innovative tube-to-tube contact modeling is applied. The high precision results are accomplished by running a dynamic finite element simulation. The basic principle is to evaluate the plunger load incrementally by consecutively applying restarts of each time step, fully automated and computation time optimized. This publication shows that both the plunger load and the rod string’s dynamic behavior can be determined for any given wellbore as long as the borehole trajectory and surface dynamometer measurements are known. The dynamic finite element model is evaluated for a deviated system and a vertical system equipped with two different downhole pump types. Comparing the simulation results with the available downhole measurements and the analytical solution shows an excellent match, whereas the proposed solution provides a considerable amount of details about the overall system’s behavior. The evaluation has shown that the performance of standard and novel downhole pump types can be successfully diagnosed in detail, which is just possible under limitations with commercial software solutions. This tool can correctly predict whether or not the sucker rod string is subjected to buckling during the downstroke, which has a considerable effect on increasing the mean time between failures of a sucker rod pumping system. From the economic point of view, this means that the economic limit of a wellbore can be postponed. The novelty of the shown technique is the consideration of the full 3D trajectory and the implementation of only physical properties, result in an excellent accuracy of the output.

A simulation model for dynamic behavior of directional sucker-rod pumping wells: implementation, analysis, and optimization

Sucker-rod pumping wells can be either vertical or directional. Over time, research efforts on the functioning of vertical wells led to a well-established set of mathematical models and practical tools. When it comes to directional wells, however, no general agreement has been reached, and the topic remains in active discussion. This paper revisits, extends, implements and optimizes an overlooked model, initially devised in 1995, whose computational complexity resulted in long processing times that stymied its adoption. This model fully utilizes the 3D trajectory of the rod string, allowing for the use of two viscous friction models and proposing its own formulation for downhole boundary conditions. The resulting model can be used to efficiently simulate the dynamic behavior of directional sucker-rod pumping wells taking into account the fluid flow inside the rod-tubing annulus. We present and analyze a serial and a parallel software implementation of this CPU-intensive model based on an explicit finite-difference method. We also describe our contributions to the accuracy and performance of the original model and software implementation. A rough approximation shows that the proposed serial version is about 200 times faster than the legacy original code, if we were to run the latter in a modern processor. On top of that our parallel implementation achieved a 6.5times speedup over the serial version in a shared-memory system, making it a suitable tool for well design and optimization. The research contributes to the discussions on mathematical modeling of directional sucker-rod pumping wells, and illustrates how performance-focused techniques can enable the effective use of computationally demanding models to facilitate further refinements and applications.

AN APPROACH TO ESTIMATING THE RATE OF ORGANIC DEPOSIT FORMATION IN A HOLLOW ROD STRING AND SELECTION OF METHODS FOR DEPOSIT PREVENTION

Background. There is currently a lack of a methodology that can enable highly-precise determinations of rates of asphaltene deposit (AD) formations in case of dual operation of two oil reservoirs via a single multi-zone oil-producing well using small-bore hollow rods as part of downhole pumping equipment. This methodology aims to minimize the costs of oil and gas companies for servicing such oil wells and preventing their failure. Aims. Creating a methodology aimed at accurate quantitative estimations of the organic deposit formation rates at the inner part of the hollow rod strings. Methods. Calculations of temperature distributions along the hollow rod string inner surface; graphic presentations of the calculated data; laboratory tests using a Cold Finger unit for the selected sections of the hollow rod strings and the graphic presentations of the results. Results and Discussion. The suggested algorithm was field-tested at a target multi-zone oil-producing well of Pavlovka oil field in Perm Krai of the Russian Federation. Using the suggested algorithm, a variation in organic deposit formation rates along the hollow rod string length was evaluated, and the depth of the maximum deposit formation rate was determined. To prevent the deposits in question along the hollow rod string at a target oil-producing well of Pavlovka oil field, laboratory tests were conducted to determine the efficiency of employing the chemical technology, i.e., the use of AD inhibitors, as well as a technology for the removal of the formed deposits using AD solvents. Conclusions. The proposed algorithm is more accurate and requires less time and money compared to existing algorithms. It enables the most effective evaluation of the formation depth of the organic deposits and the intensity at these marks. When evaluating the laboratory studies results, it can be noted that the use of the considered technologies to eliminate organic deposits is highly effective and can be used for this purpose.

Sucker Rod Antibuckling System: Development and Field Application

SummaryWhen the oil price is low, cost optimization is vital, especially in mature oil fields. Reducing lifting costs by increasing the mean time between failure and the overall system efficiency helps to keep wells economical and increase the final recovery factor. A significant portion of artificially lifted wells currently use sucker rod pumping systems. Although its efficiency is in the upper range, there is still room for improvement compared with other artificial-lift systems.This paper presents the field-tested sucker rod antibuckling system (SRABS), which prevents buckling of the entire sucker rod string, achieved by a redesign of the standing valve, the advantageous use of the dynamic liquid level, and, on a case-by-case basis, application of a tension element. The system allows full buckling prevention and a reduction of the overall stresses in the sucker rod string.The resulting reduction in the number of well interventions combined with the higher system efficiency prolongs economic production in mature oil fields, even in times of low oil prices. The analysis of SRABS, using finite-element simulations, showed a significant increase in system efficiency. The SRABS performance and wear tests under large-scale conditions were performed at Montanuniversität Leoben’s Pump Test Facility and in the oil field. The results of intensive laboratory testing were used to optimize the pump-body geometry and improve the wear resistance by selecting optimal materials for the individual pump components. The ongoing field-test evaluation confirmed the theoretical approach and showed the benefits achieved by using SRABS. SRABS itself can be applied within every sucker rod pumping system; the installation is as convenient as a standard pump, and manufacturing costs are comparable with those of a standard pump.This paper shows improved performance of the SRABS pumping system compared with a standard sucker rod pump. SRABS is one of the first systems that prevents the sucker rod string from buckling without any additional equipment, such as sinker bars. Testing of SRABS has identified significant benefits compared with standard sucker rod pumps.

Progressing-Cavity-Pump Configuration Addresses Operational Challenges

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201130, “Novel Progressing-Cavity-Pump Configurations Address Operational Challenges,” by Lonnie Dunn, SPE, Ryan Rowan, and Abhishek Prakash, Lifting Solution, et al., prepared for the 2020 SPE Virtual Artificial Lift Conference and Exhibition-Americas, 10-12 November. The paper has not been peer reviewed. While downhole progressing-cavity-pump (PCP) designs provide options for end users, the numerous products available, combined with a lack of industry standardization, can make selection and application challenging. The complete paper provides an overview of the development of a PCP concept and implementation, which is not included in this synopsis, and then summarizes two novel PCP configurations deployed to address specific operational challenges. Design and Manufacturing, Configuration 1 A novel PCP configuration was developed from phased design trials and experience in cold heavy-oil production with sand (CHOPS) wells. This configuration uses a modified rotor to create alternating sections of contact and noncontact within a conventional stator (Fig. 1). The rotor is landed in the stator and operated until there is a performance decline. Then, the rotor is repositioned to move the active section of the rotor into the areas of the stator where there originally was no contact and, as such, normally no associated damage. Keeping the length of the alternating sections short simplifies the surface rotor positioning process, allowing it to be performed riglessly. The main benefit of this is that, rather than having to pull the rod string and run a different rotor, the same rotor is used and repositioned through lifting of the rod string at surface.

Calculation of shock absorber parameters of torsional vibrations of screw pumps’ rod string

Torsional vibrations of the rod string occur during the operation of surface-driven screw pumping units, which reduces the reliability of the units. It is proposed to include a torsional vibration damper in the rod string to maintain stability. The calculation of the parameters of the shock absorber is presented.

Technological Features of Well Equipment Work under Production of Oils with Increased and High Viscosity

Fields with hard-to-recover reserves include formations with small oil-saturated thickness, low-permeable reservoirs and formations with great depth of occurrence. Oil recovery from these fields is entailed by premature failures of well equipment. To increase technological efficiency of production of high-viscous oils of the well stock equipped with walking beam pumping unit (WBPU) it is proposed to use sucker-rod pump with an external weighting agent. Introduction of this type of pumps will allow increasing the value of minimum load on sucker-rod string during its downward stroke, which will reduce the value of amplitude loads. Additional load, created by external weighting agent, will prevent the rod string from hovering due to high hydrodynamic friction forces caused by the increased and high viscosity of the pumped fluid. The technological efficiency of introducing this pump in wells with WBPU is demonstrated. Calculations made allow us to determine necessary weight of heavy bottom according to viscosity of the produced fluid.

Method for calculating dynamic loads and energy consumption of a sucker rod installation with an automatic balancing system

The efficiency of sucker rod pump installations, which have become widespread in mechanized lift practice, is largely determined by the balance of the drive. During the operation of sucker rod installations, the balance of loads acting on the rod string and the drive can change significantly due to changes in the dynamic fluid level, which leads to a decrease in balance and an increase in loads on the pumping equipment units. The increase and decrease in the dynamic level in accordance with the pumping and accumulation cycle occurs in wells operating in the periodic pumping mode. 
 It is shown that during the operation of equipment in a periodic mode, fluctuations in the dynamic level and, accordingly, in the loads acting on the nodes occur. This leads to the need for dynamic adjustment of the balancing weights to ensure the balance of the pumping unit. A system for automatic balancing of the rod drive has been developed, including a balancing counterweight, an electric motor that moves the load along the balance beam, a propeller and a computing unit.
 To study the effectiveness of the proposed device, a complex mathematical model of the joint operation of the reservoir - well - sucker rod pump - rod string – pumping unit has been developed. It is shown that due to the dynamic adjustment of the balance counterweight position, the automatic balancing system makes it possible to significantly reduce the amplitude value of the torque on the crank shaft (in comparison with the traditional rod installation) and provide a more uniform load of the electric motor. Equalization of torque and motor load reduces the power consumption of the unit.

Расчет нагрузки на штанговую подвеску при неустановившемся колебательном движении штанг скважинной насосной установки

The efficiency of a rod pumping unit is determined by the straightness of its rod string, which is impacted by the load when the rod string is in motion. Determining the dependence of the load impacting the rod suspension on the dynamic forces is one of the major issues in ensuring its straightness. In order to provide equal distribution of the stresses along the entire length of the polished rod under dynamic loading, it is necessary to determine the load on its surface, which is impossible without the equation of unsteady motion of the rod string. To this end, the article examines the issues related to the equation of unstable motion of well pumping unit rods. Formulae for calculating the loads acting on the rod suspension point are derived, and the equation of the rod string motion and load on the polished rod after the initial deformation is obtained.

Amelotin-Mediated Crystals Assembly in Liquid-Phase and on Tooth Surface

Objectives: To study the role of amelotin in enamel formation, purified recombinant human amelotin was used in a study of amelotin self assembly and its role in new HAP crstal structure formation in a laboratory setting. Methods: The full-length human amelotin gene was cloned from developing tooth buds and recombinant amelotin was expressed and purified. Morphological changes during amelotin self-assembly and the role of amelotin in promoting new minieralization structure is studied using Transmission electronic microscopy and Scanning electron microscopy. Results: The measured molecular weight of expressed human amelotin was 28 kDa that matches the predicted values. Amelotin self-assembles to form nano-spheres 10 - 30 nm in size. The amelotin self-assembly process further produces higher 3-D structure in the forms of chain-like fabric arranged in parallel and perpendicular direction. The neonatal pearl crystals were arranged side by side to form a string of small rods and small parallel rods extend from the demineralized glaze on the surface of teeth that were pre-treated with amelotin.

Numerical simulation of plane flow field and the force on the inner rod induced by planetary motion of the rod string

In order to a the flow of the plane flow field induced by the inner rod rotates and revolves in the cylinder, the Fluent software is used to numerically simulate the plane flow field of the eccentric annulus generated by the planetary motion of the rod string and based on the superposition principle. The velocity distribution and secondary flow of the two flow fields, as well as the fluid force on the inner rod are analyzed. The calculation results show that the flow field induced by the eccentric rotation of the inner rod and the self-rotation of the outer cylinder is quite different from the planetary motion of the inner rod. When rotation of the inner rod has the same direction with the revolution direction, the fluid velocity distribution near the wall of the inner rod is that the velocity on the narrow space side of the annulus is large, and on the wide space side is small. There is a critical value of eccentricity for secondary flow appears when the eccentricity is greater than this value. When rotation of the inner rod is contrary to the revolution, the fluid velocity distribution near the wall of the inner rod is that the velocity on the wide space side of the annulus is large, on the narrow space side is small. Different eccentricity has obvious secondary flow phenomenon where appears in a wide gap and close to the inner rod. When the inner rod revolves, there is a critical value of eccentricity, the inner rod is pushed outward by the fluid force when the eccentricity is less than this critical value. On the contrary, the inner rod is pushed inward. When rotation and revolution are reversed, the critical value of eccentricity increases, when the rotation and revolution are in the same direction, the critical value of eccentricity decreases.

Оптимизация технологического режима работы установок скважинных штанговых насосов с комбинированной стеклопластиковой штанговой колонной

Оптимизация технологического режима работы установок скважинных штанговых насосов с комбинированной стеклопластиковой штанговой колонной

Downhole Dynamometer Sensors for Sucker Rod Pumps

This publication introduces the downhole dynamometer sensor technology for digitalizing sucker rod pumps’ downhole behavior. The presented field application enables insight into the sensor principles, data evaluation processes and highlights the value chain. Sucker rod pumps (SRP) are used worldwide since the last century. Nevertheless, the system is still prone to fail in certain situations. The lack of measured downhole data is a severe problem that significantly slows down the innovation process. The presented downhole dynamometer sensor measurement system can successfully fill this gap and provides valuable, requested information. Each downhole dynamometer sensor records the three-dimensional stress field, the movement characteristics, and the produced fluid temperature. The recorded data allow a critical evaluation of the rod string behavior. Rod string loading and movement, friction forces between rod guides and tubing, and volumetric parameters can be evaluated. The recordings of several sensors are linked together to provide a comprehensive picture of the sucker rod string condition. The field case data analysis has indicated severe wear at specific positions of the sucker rod string and shown a significant optimization potential of the system. This publication shows the significant optimization potential for the tested sucker rod pumping system to postpone the economic limit and increase the recovery factor. The novelty is the wealth of information obtained and the associated detailed evaluation possibilities.

Predicting multi-tapered sucker-rod pumping systems with the analytical solution

The sucker-rod string is an important part of the sucker-rod pumping system. Many methods have been employed to solve the one-dimensional wave equation that describes the longitudinal vibration of the sucker-rod string. The analytical solution with the separation of variables method is an important method. However, the analytical solution is mainly applied for diagnostic analysis and is difficultly applied for predictive analysis. As a result, the characteristics of predictive analysis for multi-tapered sucker-rod string with the analytical solution are misunderstood.In this paper, the analytical solution easily applied for predicting the behaviors of multi-tapered sucker-rod pumping systems is proposed after the general analytical solution of the separation variable method is expressed with a matrix. Based on the same parameters and boundary condition, the prediction results between the analytical solution and the finite differential solution, which is extensively applied to solve the wave equation, are compared; the parameter sensitivity in the predictive analysis of the sampling point number, Fourier coefficient number and viscous damping factor value are explored; and the prediction characteristics of different tapered rod string are simulated.The simulation results show that the polished rod card predicted by the analytical solution has a smooth effect and that the sharp corners of the pump card can be precisely described compared with the finite difference method in the predicate analyses. With an increase in the stage number from 1 to 4 of the sucker-rod string, the program execution time ratio between the finite differential solution and the analytical solution is exponentially increasing from 4.7 to 10.5. The optimal Fourier coefficients number is half of the sample point number; otherwise, there will exist the Gibbs phenomenon in the pump load approximated by the truncated Fourier series. For the same viscous damping factor, the prediction results of the two methods differ, and the analytical solution is insensitive to the viscous damping factor. With an increase in the stage number of the sucker-rod string for the same total length, the polished rod load decreases while the pump stroke may decrease.Eventually, the predicted polished rod card calculated according to the field parameters shows a satisfactory correspondence with the measured card, indicating that the model presented in this paper is feasible.

Development of a method for wireless information transmission in wells equipped with sucker rod pump units

Oil lifting via sucker rod pump units is the most widespread way to extract oil reservoir products. Complications adversely affecting the operation of downhole equipment and entailing increased wear and premature failure of sucker rod pump units arise in the process of high-viscosity oil production. The pressure and temperature of the well fluid are the main parameters for assessing changes in the properties of the extracted products and for determining the static level of the liquid column. It is possible to control pressure and temperature using sensors located in the immediate vicinity of the well pump. Today, a wired channel is the main way of transmitting the measured data to the well mouth. The present work proposes a new technical solution for a wireless communication channel along tubing strings and rods. The columns are separated by asphaltenes deposits on the surface of the columns and centralizers mounted on the rods. The rod string isolation from the tubing string at the wellhead is carried out through suspension modernization. Columns are closed inside the pump, specifically, on the cylinder-plunger contact. Information is transmitted from the bottom by means of a submersible module, consisting of an electrical separator and electronic circuit. The latter controls the separator closure and opening. The results of measurements of the resistance between the columns indicate the possibility of implementing a communication channel.

Nonlinear Finite Element Analysis of Rod String in Rod Pumping System

Rod pumping is the main oil recovery method at home and abroad. The corresponding displacement and load of the sucker rod section are important parameters in the system. This paper uses the advantages of the finite element method to solve the three nonlinear problems in the rod string model, and establishes its finite element analysis model. According to the upper and lower boundary conditions and initial conditions, the software is used to program and calculate. The surface dynamometer card of multi-level steel rod columns and glass fiber reinforced plastics-steel hybrid rod string is predicted, and the calculation results with and without considering mass nonlinearity are compared and analyzed. The feasibility of predicting the surface dynamometer card by the finite element method is verified. It is proved that the coupling has a great influence on the mechanical properties of the glass fiber reinforced plastics-steel hybrid rod string.

Pumping wells super flexible closed-loop control technology research and testing applications

In the late period of oilfield development, beam pumping is the most common artificial lifting method. With many problems such as high energy consumption, low efficiency and poor working condition, conventional drive control and production management mode can hardly meet the need of development. In this paper, a method of super flexible closed-loop control for beam pumps is proposed. With coupling analysis of loads, power and position of crank in a pump cycle and calculating, motor speed and corresponding frequency output curve can be obtained. Thus, variable motor speed with very little change on power mode is achieved. Through the driving frequency output and the drive power change, the variation of loads, torque and power of the whole beam pumping system can be reduced. In this way, working condition and efficiency of the pump can be improved and the abrasion of rod string and energy consumption can be reduced, meanwhile, service life of the whole system can be prolonged. After field test, the result of energy saving and efficiency improving can be seen.

Development and implementation of device for capturing large mechanical particles falling into the space between cylinder and plunger of sucker-rod pump

The deep pump, mainly sucker-rod deep pumping method is widely applied in the onshore oil wells of Azerbaijan. Despite the fact that the deep-well sucker rod pumping method is widespread, its operation in sand-producing wells is accompanied by various complications. Since mechanical particles wearing the pump parts out, falling into the space between the plunger and the cylinder, either wedge the plunger inside the cylinder or increase the gap between them. To prevent the ingress of large particles of sand into the gap between the plunger and the cylinder of the deep sucker rod pump, a device for sand trapping has been developed. The sand-trapping device is installed within the well tubing strings on the rod string and prevents the big particles of the liquid in the pipes falling into the gap between the plunger and cylinder. As the plunger, the device is started via balanced head. Due to the equipment installation, the liquid injected from the pump undergoes pressure decrease and the conditions for deposition and accumulation of large particles are formed.

Spatial Transverse Vibration Simulation Model of Axially Moving Sucker Rod String under the Excitation of Curved Borehole

The mechanical model of transverse vibration of sucker rod string (SRS) in directional well is simplified to the transverse vibration model of longitudinal and transverse curved beam with initial bending under borehole constraints. In this paper, besides considering the excitation of alternating axial load on the transverse vibration of SRS, it is proposed for the first time that curved borehole is also the main excitation for the transverse vibration when the SRS moves reciprocating axially in the borehole. Based on the elastic body vibration theory, the transverse vibration mathematical model of SRS with initial bending under borehole constraints is established. In this model, the curved borehole excitation caused by the axial motion and the alternating axial load excitation is considered. Besides, the elastic collision theory is applied to describe the constraint of tube on the SRS transverse vibration in this model. Then the fourth-order Runge–Kutta method is used to calculate the transverse vibration of SRS in directional wells. The simulation results show the following: (1) The simulation results of the three simulation models in this paper are different. The results indicate that the curved borehole excitation caused by the axial motion and the alternating axial load excitation is the main excitation for the SRS transverse vibration. (2) In directional wells, the rod and tube contact along the well depth, and the dangerous sections locate at the deviation section of the borehole and the compression section of the rod. On the whole, the contact force between rod and tube in deviation section of borehole is larger. The transverse vibration of the compression section of the rod is the most violent.