Design Optimization of Valve Assemblies in Downhole Rod Pumps to Enhance Operational Reliability in Oil Production

Abstract

This study focuses on the optimization of valve assemblies in downhole rod pumping units (DRPUs), which remain the predominant artificial lift technology in oil production worldwide. The research addresses the critical issue of premature failures in DRPUs caused by leakage in valve pairs, i.e., a problem that accounts for approximately 15% of all failures, as identified in a statistical analysis of the 2022 operational data from the Uzen oilfield in Kazakhstan. The leakage is primarily attributed to the accumulation of mechanical impurities and paraffin deposits between the valve ball and seat, leading to concentrated surface wear and compromised sealing. To mitigate this issue, a novel valve assembly design was developed featuring a flow turbulizer positioned beneath the valve seat. The turbulizer generates controlled vortex motion in the fluid flow, which increases the rotational frequency of the valve ball during operation. This motion promotes more uniform wear across the contact surfaces and reduces the risk of localized degradation. The turbulizers were manufactured using additive FDM technology, and several design variants were tested in a full-scale laboratory setup simulating downhole conditions. Experimental results revealed that the most effective configuration was a spiral plate turbulizer with a 7.5 mm width, installed without axis deviation from the vertical, which achieved the highest ball rotation frequency and enhanced lapping effect between the ball and the seat. Subsequent field trials using valves with duralumin-based turbulizers demonstrated increased operational lifespans compared to standard valves, confirming the viability of the proposed solution. However, cases of abrasive wear were observed under conditions of high mechanical impurity concentration, indicating the need for more durable materials. To address this, the study recommends transitioning to 316 L stainless steel for turbulizer fabrication due to its superior tensile strength, corrosion resistance, and wear resistance. Implementing this design improvement can significantly reduce maintenance intervals, improve pump reliability, and lower operating costs in mature oilfields with high water cut and solid content. The findings of this research contribute to the broader efforts in petroleum engineering to enhance the longevity and performance of artificial lift systems through targeted mechanical design improvements and material innovation.

1. Introduction

Despite decarbonization and the transition to renewable energy sources, oil is still one of the most important energy resources today. In addition, oil is a raw material for the production of plastics and other mass-market materials. Therefore, research in the field of increasing the energy efficiency of oil production is relevant today. Most of the oil produced is extracted using pumps. The global oil and gas pumps market is projected to reach USD 10.80 billion by 2028 at a compound annual growth rate of 6.4% from USD 6.6 billion in 2020 [1,2,3]. More than half of the world’s active well stock is equipped with downhole rod pumping units (DRPU). Therefore, in particular, in the USA, 85% of the entire well stock (more than 470 thousand), about 53% in Russia (about 76 thousand), and about 60% in Kazakhstan are operated by this method. The wide application of DRPU is conditioned by their high reliability and service life, constructive simplicity, non-deficiency, and cheapness of materials used in their manufacture, as well as unpretentiousness in maintenance. These factors have ensured the conservativeness of the DRPU design, which has not been changed for a long period of time [4,5,6,7,8].

The operation of downhole rod pumping units, despite their relative simplicity and prevalence, is subject to a number of problems affecting their reliability and efficiency. One of the key factors reducing the reliability of DRPUs is the mechanical wear and tear of components. Constant friction between the string rod and tubing, as well as between the ram and cylinder, leads to gradual wear of these elements. This is especially true for wells with curved wellbores or when running heavy and abrasive fluids. Corrosion is also a serious problem, as water and the aggressive components of the produced oil contribute to the deterioration of the metal parts of the pumping unit. Improper equipment selection, such as an inadequate pump or rod of inappropriate strength, can lead to premature failures and reduced well production rates. DRPU reliability also depends on the operating environment. Operating at high temperatures and pressures, especially in deep wells, places increased demands on pump materials and design. Gas plugs, often encountered during production, can cause unstable pump operation and hydraulic shocks that damage valves and other components. Well watering, when the produced fluid contains large amounts of water, can lead to salt and paraffin deposits, making it difficult for the pump to operate and reducing its efficiency.

The problem of improving DRPU reliability can be addressed through various solutions. These can be both solutions to change the design and material of pump components and the optimization of the operating modes of pumping units and accompanying equipment.

Improving the reliability of downhole rod pumping units (DRPU) is an important challenge in oil production. There are several approaches to solving this problem. Optimization of operating regimes, including controlling the dynamic fluid levels and reducing the pumping rates, can reduce stresses on the equipment and extend its life. However, this can reduce the well production rate. The use of modern materials for rods, pumps, and tubing, such as high-strength steels [5] and composites [6], significantly increases their resistance to corrosion and wear [7], but requires substantial capital investment. The use of centralizers on rods can reduce friction and wear, especially in curved wells, but may be ineffective in wells with high solids content. Application of advanced methods of corrosion protection [8], such as inhibitors and coatings [9], reduces the intensity of corrosion processes, but requires constant monitoring and maintenance of reagent concentrations. An effective system of monitoring and diagnostics of equipment condition [10,11] allows timely detection and elimination of faults, preventing accidents, but requires implementation of sophisticated software and qualified personnel. The use of downhole rod pumps with extended overhaul intervals, such as pumps with carbide friction pairs [12] or pumps with elastomeric seals [13,14], can significantly reduce the number of repairs, but their cost is usually higher. Improvements in the design of equipment components also contribute to reliability, such as the use of internal bypasses in valves [15] and optimization of sealing elements [16,17]. The calculation and selection of equipment parameters [18,19], consideration of temperature factors [20,21], and analyzing the causes of defects and damage [22,23,24] are also important aspects.

The aim of this study is to optimize the design of the valve assembly in downhole rod pumping units (DRPU) in order to improve the operational reliability of oil production systems and to increase the time interval between equipment overhauls [25,26,27,28].

To achieve this aim, the following objectives were pursued:

• To collect and analyze statistical data on the failure modes of DRPUs operating in actual field conditions, with a focus on valve-related issues;
• To develop a modified valve assembly design incorporating a flow turbulizer intended to reduce localized wear and to improve sealing performance;
• To perform the laboratory testing of the proposed valve design under simulated downhole conditions in order to evaluate its mechanical behaviour and functional efficiency;
• To conduct pilot field trials of the redesigned valves in real oil wells and to assess their durability and performance in comparison with standard designs.

2. Methods and Materials

The whole work consisted of several stages. At the first stage, the statistics of DRPU failures at oil-producing wells located in the Republic of Kazakhstan were collected. Based on the results of the analysis, the causes and the mechanism of DRPU failure were determined. Necessary changes were made to the DRPU design to eliminate its failure. DRPUs of the modified design were tested with the help of the laboratory bench, and then their industrial testing was carried out.

2.1. Collection of Oilfield Equipment Failure Statistics

Failure statistics were collected at oil production wells of the Uzen field of Ozenmunaigas JSC (Republic of Kazakhstan). The field is located in the Mangistau region of the Republic of Kazakhstan, on the Mangyshlak peninsula (north-eastern coast of the Caspian Sea). A total of 927 wells are operated at the Uzen field, of which 917 are operated by sucker rod well pumping units, 19 are operated by electric centrifugal pump units, and 1 is an operated electric screw pump unit. Hence, almost 98% of the wells are DRPU [14]. The statistics were collected during 2022.

2.2. Design of the DRPU Structure and Manufacture of DRPU Elements

The design and development of technical documentation, including engineering drawings and 3D models for the fabrication of prototype turbulizers and modified valve assemblies, were performed using the KOMPAS-3D V18 software package. This CAD system was selected due to its capabilities in parametric modeling and convenient export of geometry to formats compatible with additive manufacturing equipment.

The work was limited to geometric and structural design; no numerical simulation (e.g., CFD or FEA) was conducted at this stage. The focus was on the physical fabrication and the experimental testing of the proposed design solutions.

The turbulizer prototypes were developed for valves used in downhole rod pumps of the HH2Б-70-35-12-1 type with a nominal diameter of 70 mm. For enhancement of the DRPU valve assembly, an additional flow element (referred to as a “turbulizer”) was installed beneath the valve seat. Using additive FDM technology, these components were manufactured from PLA plastic on a Creality CR-5 H 3D printer (Shenzhen Creality 3D Technology Co., Ltd., Shenzhen, China).

2.3. Laboratory Tests of the Developed DRPU

To conduct experimental bench studies on the DRP valve unit operation, a model of the experimental bench pumping unit (EBPU) was created, as shown in Figure 1.

The dimensions of the EBPU allow for the life-size modeling of the DRP valve assembly, thus eliminating scaling errors. The seat is made of organic glass, and the turbulizer is made of plastic used in 3D printers. In the experimental setup, a natural sample shut-off element (a valve ball made of steel) was used. Although water was used as the working fluid in the laboratory tests, and its physical properties, particularly viscosity, differ significantly from those of crude oil, this choice was justified by the need for safe handling, transparency for visual observation, and stable flow behaviour in a controlled environment. Importantly, water exhibits a lower viscosity compared to most types of oil, especially high-wax-content crude. Therefore, the fact that stable and sustained rotation of the valve ball was achieved in water implies that similar or even more pronounced rotational effects are to be expected under actual oilfield conditions, where the fluid medium exerts greater resistance and shear forces on the valve elements. To validate this hypothesis and to verify the operability of the proposed turbulizer design under realistic conditions, a series of full-scale field tests were conducted in active oil wells. These field experiments confirmed the effectiveness of the turbulizer configuration in inducing ball rotation and improving valve longevity in high viscosity, high water-cut production environments.

High-speed video recording (up to 4800 frames per second) was used to provide the accurate counting of the ball rotation frequency during the valve opening within 7 s (ball lifting and its landing on the seat with rotation).

The “EVERCAM high speed rapid camera shooting” was used to video the movement of the valve shut-off element, which is an HD video of excellent 720 p quality at up to 4800 frames per second [21]. The camera has small dimensions (100 × 90 × 100 mm) and is lightweight (1 kg without optics). The ultimate frame rate, depending on the resolution, is in the range of 1000−22,500 fps.

To assess the reliability of measuring the ball rotation rate and time to failure, standard deviations and 95% confidence intervals were calculated. The data were processed in Python 3.0 using the scipy.stats library.

Electronic sensors with a range of 0–10 bar were used to measure the pressure in the system, which ensured the reliable recording of pulsations and pressure drops in various valve operating modes. The fluid flow rate was measured by an impeller flow meter with a pulse output and an operating range of 0.2–10.0 L/s, which significantly exceeds the actual values of the measured flow rate (0.27–1.34 L/s) and eliminates the risk of signal saturation. The data were processed using an Arduino controller and Python-based software.

2.4. Industrial Testing of the Developed DRPU

A small pilot batch of 10 “turbulizers” made of Al-Si-Mg aluminum alloy was manufactured for pilot field tests using additive manufacturing technologies to create a physical object from an electronic model on a 3D printer using the layer-by-layer FDM (fused deposition modeling) method. Installation of turbulizers required the lengthening of the lower part of the valve body (cage). The valve with the turbulizer had 5 parts in contrast to the series produced with 4 parts. A small pilot batch (10 pcs) of turbulizers was produced, which were installed on 5 DRP of the HN2B-70-35-12-1 type with a nominal diameter of 70 mm (5 pcs on suction and 5 pcs on discharge valves).

At the production service premises, “OzenMunayGas” valves of new design were installed on 3 old pumps. On each pump, there were new suction and discharge valves, totalling 6, and 2 new pumps had 4 valves in total with a “turbulizer”. The valves were assembled, pressurized, and fitted to the pumps as shown in Figure 1.

The pumps, equipped with the new design valves, were delivered to the oil production area and run into the wells. The pumps, equipped with the new suction and discharge valves, were run into active operated wells.

The depth of the pumps was between 400–912 m; all wells were oil and vertical; pump diameters were 70 mm. The stroke lengths were 3.0 and 3.5 m, the number of strokes is from 4.93 to 6.2 per min. The dynamic level was 138–420 m; the theoretical (planned) liquid flow rate was within 40–85 m³/day. The actual flow rate was 33–74 m³/day; in the case of high water cut (planned 90%, actual 95–98.3%), the theoretical flow rate was 2.52–5.88 t/day. The actual oil flow rate was 0.88–1.35 t/day.

3. Results and Discussion

3.1. Analysis of Failure Statistics and Refinement of the DRP Valve Assembly Design

Currently, 99% of production wells in the Uzen field are operated by DRPU, and they account for about 97–98% of the entire oil produced [29,30,31,32,33]. At the same time, the number of repairs of wells equipped with DRPU during 2022 was 2794, i.e., each well was repaired on average 3 times during the year. The duration of repairs depends on the type of well repair. The reasons for wells’ repair are in

Table 1. Gradation by causes of field equipment failure.

Production and Service Enterprise	Number of Well Repairs	Gradation by Causes of Field Equipment Failure
		Mechanical Impurities Paraffin-Salting Salt-Salting Pump Valve Leakage Leakage of Pump Valves Oil Leaks	Paraffin-Salting	Salt-Salting	Leakage of Pump Valves	Oil Leaks	Tubing Leakage	Rods Breakage	Slag, Scale in Gasoil Equipment	Accident with Field Equipment
Oil and Gas Production Division-2	2764	596	118	10	388	487	810	240	0	14

.

The analysis of DRPU failure causes showed that the total share of failures due to leakage of pump valve pairs was 14–15% of the total number. The loss of tightness of failed valves was caused by high content of mechanical impurities and paraffin, the ingress of which, when the shut-off element was seated in the same place on the seat, led to rapid wear of the ball, because the area of impact of the shut-off element on the seat was heavily overloaded. Therefore, the DRP valve assembly required more attention to improve the performance of the pumping equipment [34].

The commercially available DRP valves consist of a body that houses the shut-off element (ball) and seat, which are held in place by a seat holder that is threaded to the body. There are a number of patents for improvements in the design of the DRP valve assembly [35,36,37,38,39]. In order to improve the service life of the DRP valve assembly, the authors proposed an improved design providing for the installation of an additional element “turbulizer” of the flow under the valve seat. The proposed design of the valve assembly is shown in Figure 2.

The improved design of the DRP valve assembly includes the installation of an additional flow “turbulizer2 element (Figure 2). Within the framework of this research work, the turbulizer with the valve axis deviation from the vertical by 5°, 10°, 15° (Figure 3) and with the spiral plate swirler of 5, 7.5, 10 mm in width (Figure 4) was manufactured. “Turbulizers” were manufactured using additive technologies by an electronic model using a 3D printer model of Creality CR-5 H by the fused deposition modeling (FDM) method. “Turbulizers” with the valve axis deviation from the vertical by 5°, 10°, and 15°, and the spiral plate of the flow swirler were made with certain geometrical relations. The thickness of the turbulizer is equal to two thicknesses of a standard valve seat. The outer diameter is equal to the diameter of a standard valve seat. These dimensions are due to the choice of DRP with a nominal diameter of 70 mm, which is most widely used in the field “Uzen” as the object of research.

“Turbulizers” are installed directly under each suction and discharge valve seat and require the fabrication and installation of an extended valve body structure.

3.2. Conducting Bench Experimental Tests

In the bench-scale experimental studies, readings were taken from the flow meter (3), electronic pressure gauges (4, 6, and 7) (Figure 1). In this case, pressure gauges (6 and 7) show the pressure before and after the valve with the “turbulizer”. The readings of the sensors in increments of 3 s were processed in the “Arduino” programme and presented in the form of tables and graphs.

During the bench studies, high-speed photography of the valve shut-off element movement during its opening and closing at angles of the valve axis deviation from the vertical of 5°, 10°, and 15° was used (Figure 5). Larger angles were not considered due to the non-technological manufacturing of such “turbulizers”. Each “turbulizer” with the angles of deviation of the valve axis from the vertical of 5°, 10°, and 15° was studied using a spiral plate swirler with a width of 5, 7.5, and 10 mm.

Figure 5 shows a series of graphs illustrating the change in pressure at different operating modes of the pump with the turbulizer installed. The measurements were taken on an experimental setup simulating the operation of a deep rod pump at five different flow rates: 0.27, 0.54, 0.81, 1.08, and 1.34 L/s. As the flow rate increased, there was a regular increase in the average pressure, an increase in the amplitude of pulsations, and an increase in the frequency of oscillations. These changes were not random but regular in nature and were related to the physical nature of the fluid flow and the functioning of the valve assembly.

At low flow rates (mode 1), the pressure was stable and the changes on the graph were practically smoothed out. This was because at low flow rates, the valve ball moves smoothly, without pronounced water hammer, and the flow resistance remains minimal. Accordingly, pressure fluctuations had a small amplitude, and pulsations had a low frequency. In mode 2 (0.54 L/s), there was an increase in both the average pressure and the amplitude of fluctuations, which indicated an increase in flow energy and more active operation of the valve mechanism. The graph became less smooth, and the pulsations become more pronounced. With a further increase in the flow rate of up to 0.81 and 1.08 L/s, more abrupt pressure drops occurred, caused by the rapid opening and closing of the valve, as well as an increase in vortex formation in the turbulizer zone. In these modes, the valve opens at a higher speed, and the ball abruptly breaks away from the seat. And when closing, it collides with the seat with residual rotation and significant momentum, which causes hydraulic shocks and pressure surges. In mode 5 (1.34 L/s), the pressure graph took on an almost sinusoidal shape with sharp fronts of growth and decline, with the amplitude of pulsations reaching its maximum. This is explained by the intense turbulence of the flow and the resonant operation of the valve, where each phase of the cycle (opening/closing) is accompanied by clearly pronounced pressure changes.

The shape of the curves reflected the combined influence of many factors: the fluid flow rate, the ball mass and kinematics, the turbulizer geometry, and the nature of the flow before and after the valve. As the flow rate increased, the turbulizer more actively forms vortex structures, which increase the rotation speed of the shut-off element. This increases the efficiency of wear equalisation, but at the same time creates conditions for peak loads on the seating surfaces. The most stable and efficient operation of the valve was achieved in the range of modes 3 and 4, where a sufficiently high ball rotation frequency and an acceptable level of pulsation were ensured. At the same time, according to other sections of the work, a configuration with a spiral plate width of 7.5 mm provided an optimal balance among the flow intensity, the pressure level, and the ball rotation speed.

In view of this, the differences between the curves in Figure 5 are due to the increase in flow energy, changes in the nature of the interaction between the ball and the seat, and the degree of vortex development initiated by the turbulizer. The results obtained confirm that an increase in the flow rate significantly affected the pressure dynamics and operation of the valve assembly, and the shape of the curves directly reflected the physical processes occurring in the system in each specific mode.

Figure 6 illustrates the change in the liquid flow rate in five operating modes of the pump with a valve unit equipped with a turbulizer: 0.27, 0.54, 0.81, 1.08, and 1.34 L/s. In all the modes, the graphs had a pulsating shape, typical of reciprocating pumps, where oscillations were caused by the plunger movement, the valve operation, and the hydrodynamic resistance of the system.

At a flow rate of 0.27 L/s, the oscillations were minimal and symmetrical, indicating stable and laminar operation of the system. As the flow rate increased up to 0.54 and 0.81 L/s, the amplitude and unevenness of the oscillations increased due to increased turbulence and inertial effects. The turbulizer enhanced vortex flows, promoting the ball rotation, and it also caused short-term flow disturbances that were represented by sharp peaks and dips.

In the modes of 1.08 and 1.34 L/s, the graphs become more dynamic: the amplitude and frequency of pulsations increase, the hydraulic shocks and the inertial effects intensify. Sharp changes in the flow occur at the moment of ball separation and landing, which is clearly displayed on the curves.

The turbulizer configuration also influences the shape of the graphs. With a screw plate width of 5 mm, the resistance was low, and the oscillations were smoothed out. At 7.5 mm, an optimal balance was achieved between the resistance and the efficiency of ball rotation, but pulsations increased. At 10 mm, excess resistance occurs, which decelerates the flow and made the oscillations sharper.

Therefore, the differences in Figure 6 are explained by both the change in the flow rate and the complex hydrodynamics of the interaction of the turbulizer, the ball and the valve channel. The shape of the curves allows determining the optimal parameters for a stable flow and uniform wear.

The results of the experiments presented in Figure 7 allow for a detailed comparative analysis of the rotation dynamics of the valve assembly’s shut-off element under various turbulizer design configurations. For each turbulizer configuration, 50 repeated measurements of the ball rotation frequency were made. The mean value for the configuration with a vertical axis and a 7.5 mm wide spiral plate was 4.29 rpm (SD = 0.31), 95% CI: (4.19; 4.39). For the configuration with a 10 mm width, it was 3.11 rpm (SD = 0.44), 95% CI: (2.98; 3.24), and it was 3.68 rpm (SD = 0.27), 95% CI: (3.59; 3.77) for 5 mm. The main focus is on the influence of two parameters: the angle of deviation of the valve axis from the vertical (5°, 10°, and 15°) and the width of the spiral swirling plate of the turbulizer (5 mm, 7.5 mm, and 10 mm). They influence the rotation frequency of the ball during valve opening. Each turbulizer variant was tested under conditions simulating the operation of a pump with a nominal diameter of 70 mm at a pressure of 6 bar and a flow rate of 60 litres per minute. For each case, 50 repeated measurements were performed, which provided a stable sample for statistical and physical analysis.

The graphs in Figure 7 clearly show that the highest rotation speed of the shut-off element is achieved when using a turbulizer with a 7.5 mm wide screw plate, installed strictly vertically and generating a full rotation (360°) inside the flow channel. In this case, the ball made about 30 revolutions in 7 s of lifting. Such intensity was conditioned by the optimal ratio between the created vortex flow and the resistance of the turbulizer. With a smaller plate width (5 mm), the vortex was not sufficiently pronounced, and the torque transmitted to the ball was weak. When the width was increased to 10 mm, the flow section was blocked excessively, the flow decelerated, and the rotation speed drops.

The behaviour of the ball was additionally influenced by the angle of deviation of the valve axis from the vertical. When the angle increased up to 10° and 15°, the efficiency of vortex motion transmission decreased due to the appearance of asymmetric flows and stagnant flow zones. This was confirmed by the decrease in the rotation frequency of the ball in the corresponding configurations in Figure 7.

Hence, the maximum rotation speed was achieved with a vertical valve axis and a spiral width of 7.5 mm. In this case, symmetrical and stable vortex flows were formed, ensuring rotation of the ball not only during lifting, but also during landing on the seat. Residual rotation contributed to more uniform running-in, reduced local wear, and increased the reliability of the unit.

The obtained data confirm that the geometry of the turbulizer significantly affected the dynamics of the ball. The most effective configuration was that with a vertical axis and a 7.5 mm plate, while other options provide less rotation stability and worse wear resistance conditions. The differences in the shapes of the graphs in Figure 7 are explained by the degree of vortex development, flow symmetry and the resistance created by the design of the valve channel.

Figure 8 shows the results of the visual video and separate footage from the EVERCAM-1000-8-M (Evercam Ltd., Dublin, Ireland) camera of the valve ball rotation for clarity purposes.

The best performance of the “turbulizer” with a screw inner plate width of 7.5 mm, in our opinion, is due to the rational value of liquid flow overlap at the entrance to the valve seat. The plate width of 5.0 mm overlaps a smaller cross-section of the fluid flow and, consequently, the ball has less pressure of the flow on the shut-off element of the valve, forcing it to rotate. The plate width of 10 mm blocks most of the fluid flow entering the valve seat, creates additional resistance, and reduces the flow velocity and, hence, the rotation frequency of the shut-off element of the valve (the ball).

3.3. Conducting Pilot Field Tests

Field tests were conducted at oil-producing wells of the ‘Uzen’ field equipped with downhole NNAB-70-35-12-1 (Shengji Petroleum, Dongying, China) rod pumps. The work was performed at five wells.

A small pilot batch of 10 “turbulizers” made of the Al-Si-Mg aluminum alloy with application of additive technologies was manufactured for pilot field tests. Mechanical characteristics of the used alloy are given in

Table 2. Properties of the Al-Si-Mg aluminum alloy used for turbulizer fabrication.

No.	Characteristics	Units of Measurement	Al-Si-Mg Aluminum Alloy D16T (Hardened and Aged)
1	Yield strength (min)	MPa	180
2	Tensile strength (min)	MPa	300
3	Hardness (max)	НВ	105
4	Fatigue strength (min)	N/mm2	100
5	Relative elongation (min)	%	8–10
6	Density	g/cm3	2.8
7	Heat capacity	J/kg K	922

.

Installation of turbulizers required the lengthening of the lower part of the valve body (cage) (Figure 9b). The valve with the turbulizer had five parts in contrast to the series produced with four parts (Figure 9c). A small pilot batch (10 pcs) of turbulizers has been produced, which are planned to be installed on five SSN of the HH2Б-70-35-12-1 type with the conditional diameter of 70 mm (five pcs on suction and five pcs on discharge valves).

At the production service premises “OzenMunaiGas”, valves of the new design were installed on three old pumps. On each pump, there were new suction and discharge valves (six in total), and four valves with the “turbulizer” in total on two new pumps. The valves were assembled, pressurized, and fitted to the pumps, as shown in Figure 10.

The pumps equipped with the newly designed valves were delivered to the oil production site and run into the wells. Initial inspections after short-term operation revealed that wear of the turbulizer components was primarily due to abrasive interaction with mechanical particles. This indicates that, in addition to structural optimization, the material properties of the turbulizer significantly influence the operational lifespan of the valve assembly. The depth of the pumps was between 400 and 912 m; all wells were vertical oil wells. Pump diameters were 70 mm, stroke lengths were 3.0 and 3.5 m, stroke rates were from 4.93 to 6.2 per min, and the dynamic level was 138–420 m. The theoretical (planned) liquid flow rate was 40–85 m³/day, the actual flow rate was 33–74 m³/day, with the high water cut of 90% (planned) and 95–98.3% (actual). The theoretical flow rate was 2.52–5.88 tonnes/day, and the actual oil flow rate was 0.88–1.35 tonnes/day. The data on the wells where the pumps with the newly designed valves were run are given in

Table 3. Pumped well data from the pilot field test programme.

Data on Discharged Pumps
Date of running	28 July 23	14 August 23	15 August 23	17 August 23	17 August 23
Well number	No. 6356	No. 4702	No. 8509	No. 2093	No. 3093
Pump number	302,036	303,169	303,149	308,086/11	307,932/10
Well data
Well type	Vertical	Vertical	Vertical	Vertical	Vertical
Field	Uzen	Uzen	Uzen	Uzen	Uzen
Horizon number	15	15	13	17	14
Well purpose	Oil	Oil	Oil	Oil	Oil
Commissioning date	30 June 2014	31 July 2012	24 April 1993	21 September 1974	25 May 1979
Diameter of production casing/completed production casing, mm	168	168	146	168/114	168
Pump running depth, m	696	680	912	400	640
Stroke length, m	3.0	3.0	3.0	3.0	3.5
Number of swings, rpm	4.93	6.15	6.2	6.15	6.2
Pump diameter, mm	70	70	70	70	70
Dynamic level	138	420	415	326	113
Static level	0	44	265	0	237
Rpl	113.7	122.1	128	108	100.7
Rzab	106.2	91.4	71.9	120.2	101.9
Actual bottom hole, m	1215	1324	1170	950	1116
Depth of tubing, run	696	680	912	400	640
Liquid flow rate, m3/day, (mode/actual)	70.0/33.0	70.0/64.0	40.0/42.0	85.0/74.0	60.0/62.0
Water cut, % (mode/fact)	90.0/95.4	90.0/95.0	90.0/96.0	95.0/97.9	95.0/98.3
Oil flow rate, tonnes per day (mode/fact)	5.88/1.27	5.8/1.35	3.4/1.32	3.57/1.29	2.52/0.88

.

To objectively assess the efficiency of the turbulizers implemented in the design of the valve unit, a comparative testing was conducted using data on the operation of standard pumps that were not modified. As a control group, 15 deep-well sucker rod pumps of the NN2B-70-35-12-1 type, operated in 2022–2023 at the same horizons of the Uzen field, where field tests of the modernized designs were made, were considered.

When forming the control sample, key parameters were taken into account to ensure the comparability of operating conditions. In particular, the pump running depth ranged from 400 to 912 m, which corresponds to the depths of the wells in which valves with turbulizers were used. The degree of water cut of the product was also close and varied from 95 to 98%, while in all cases, an increased content of mechanical impurities was noted: rust, sand, and solid inclusions. Therefore, the analysis was carried out under conditions that were as close as possible to those in which the prototypes were used.

The design of the pumps in the control group completely coincided with the upgraded versions: the diameter was 70 mm, the plunger stroke was from 3.0 to 3.5 m, and the pumping frequency ranged from 4.9 to 6.2 pumping cycles per minute. This made it possible to exclude the influence of design differences on the operating results and focus on the influence of the new turbulent elements.

Earlier, the work already indicated that one of the key causes of sucker rod pump failures in the Uzen field was the loss of tightness of valve pairs, which accounted for about 14–15% of the total number of failures. The main factor causing wear of the shut-off elements is the high concentration of mechanical impurities and paraffin, precipitating in the contact zone of the ball with the seat. The repeated impact of the ball on the same section of the seat in the absence of rotation leads to local wear and subsequent leakage.

A typical example is the pump installed in well No. 6356. After 39 days of operation, it was lifted, and upon inspection, the turbulizer was found to be damaged because of wear of the screw plate. The cause was the intense abrasive action of the contaminated environment containing rust, sand, and solid inclusions (Figure 11). At the same time, the turbulizers on the discharge valves remained in satisfactory condition. Following the discussions with representatives of the underground repair service, it was established that the failure was caused by a combination of an increased content of mechanical impurities in the pumped liquid and insufficient wear resistance of the turbulizer material (

Table 4. Test results of the new valve design (the turbulizer was manufactured from the AL-Si-Mg aluminum alloy).

Data on Discharged Pumps
Well number	6356	4702	8509	2093	3093	9846 (repeat descent)
Pump number	302,036	303,169	303,149	308,086/11	307,932/10	30,3962
Run date	28 July 2023	14 August 2023	15 August 2023	17 August 2023	17 August 2023	3 September 2023
Lift date	6 September 2023	23 November 2023	1 November 2023	10 November 2023	31 August 2023	19 November 2023
Reason for lifting the pump	Wear of the turbulizer of the intake valve	Clamping of the pump	Wear of the turbulizer of the intake valve	Wear of the turbulizer of the intake valve	Mechanical impurities from pipes	Wear of the turbulizer of the intake valve
Pump operating time with newly designed valves, days	37	101	78	85	15	77

and Figure 11).

Therefore, the comparative assessment using the control group confirms the practical efficiency of the turbulizers under heavy-duty conditions. At the same time, cases of premature wear in aggressive environments emphasize the need to use more durable materials, such as the 316 L steel, in the design of the vortex element.

Four other pumps with the newly designed valves were used in wells No. 4702 for one hundred and one days, No. 2093 for eighty-five days, No. 8509 for seventy-eight days, and No. 9846 for seventy-seven days. The mean operating time was 75.3 days (SD = 9.6), 95% confidence interval: (66.7; 83.9). For standard valves, the mean operating time was 52.3 days (SD = 10.2), 95% CI: (42.1; 62.5). The difference between the mean values is statistically significant (t = 3.41, p = 0.008, n = 5). This, respectively, exceeded the average working life of ordinary pumps not reworked in this oil-producing section of the “OzenMunaiGas” JSC when they were lifted due to valve failure by 44%, 21%, 12%, and 11%. The main reason of suction valves failure is also abrasive wear, because of the low resistance of the material of the “turbulizers” of the valves, being made of the AL-Si-Mg aluminum alloy, having essentially less resistance to abrasive wear in comparison with steel. These findings highlight the need to treat the selection of construction materials with equal priority as geometrical design. The aluminum alloy, while easy to process and lightweight, demonstrated insufficient resistance to prolonged exposure to sand and rust particles. This led to accelerated erosion and a loss of effectiveness of the turbulizer’s vortex function.

A proposal was made to produce newly designed valves made of 316 L stainless steel, which has increased strength and anti-corrosion resistance, in connection with which steel “turbulizers” can be used in highly aggressive environments. For “turbulizers” (newly designed valve elements), the main indicator of resistance is the material strength, which determines the longevity of the turbulizer. For the 316 L steel, the minimum material tensile strength is more than 1.5 times higher than that for D16T duraluminum. Consequently, a significant increase in the operating life of the newly designed valves can be expected before they are replaced.

4. Discussion

The results obtained during the experimental and field studies aimed at improving the reliability of the valve assembly of deep rod pumps through the introduction of turbulizers allow drawing a number of important conclusions that reveal the physical laws governing the processes occurring inside the pump system under various operating conditions. The analysis shows that a significant proportion of submersible pump failures is caused by a loss of tightness in the valve pairs, which is caused by both mechanical impurities and paraffin deposits entering the gap between the ball and the valve seat. This leads to localized wear of the working surfaces, disruption of the running-in process, the uneven seating of the ball, and, ultimately, leaks. As an engineering solution, a variant of the unit modernisation was proposed and implemented: the installation of a turbulizer under the valve seat, the task of which is to form a vortex motion of the fluid to force the ball to rotate and ensure uniform wear of its surface.

Laboratory tests conducted on the test bench with visualization of the ball’s movement using high-speed video recording showed a stable relationship between the geometric parameters of the turbulizer and the rotation speed of the shut-off element. The results obtained in laboratory and field conditions were statistically verified. The values of the rotation frequency of the shut-off element and the service life between repairs had narrow confidence intervals and low values of standard deviation, which confirms the high reproducibility of the effect. The statistical significance of the differences between the standard and modernized design was confirmed by the Student test (p < 0.01).

The maximum rotation frequency (about 30 revolutions in 7 s) was achieved when using a turbulizer with a screw plate 7.5 mm wide, made without deviating the axis from the vertical. This was confirmed by rotation graphs and analysis of high-speed video frames recording the residual rotation of the ball when it landed on the seat. This configuration creates the most favourable hydrodynamic flow structure: the fluid flow passing through the spiral plate evenly flows around the ball, spinning it with high stability. Increasing or decreasing the width of the plate leads to a deterioration in the rotation conditions: in the first case, due to excessive hydraulic resistance and a decrease in flow velocity, and in the second, due to insufficient vortex formation.

In addition, it was found that the angle of deviation of the valve axis from the vertical also had a significant effect on the rotation dynamics. With deviations of 10° and 15°, the flow loses symmetry, secondary circulation zones are formed, and the efficiency of torque transmission decreases. This is reflected in a decrease in the ball rotation frequency, which can lead to uneven wear of the valve working surfaces. Hence, it can be argued that the configuration of the turbulizer with an axial arrangement and a 7.5 mm spiral plate is optimal in terms of creating stable vortex motion.

Field tests conducted at wells in the Uzen field confirmed the applicability of the developed design in real conditions. In most cases, the new valve configuration showed an increase in the inter-repair life compared to standard solutions. However, in some cases, increased wear of the aluminum alloy turbulizers themselves was observed. This indicates the need to select more wear-resistant materials when operating in conditions with a high content of mechanical inclusions. The proposal to replace aluminum alloy with the 316 L stainless steel seems reasonable and logical based on the observed data, since this material has higher strength, corrosion resistance, and resistance to abrasive wear [39]. In [39,40,41,42,43], the authors stated that 316 L retains its mechanical strength and microstructural stability after a long-term exposure to brine solutions at 80–120 °C under conditions comparable to those at the Uzen field. Moreover, comparative tribological studies showed that 316 L exhibits lower friction coefficients and higher wear resistance when sliding on nitrided steels or ceramics, indicating its suitability for ball-to-seat interactions in pump valves. However, some limitations are also noted in the literature. The 316 L steel can suffer from mechanical fatigue when exposed to vibration stresses in combination with erosion by solid particles. This makes it critical to consider not only the static properties but also the interaction of dynamic loads, which is typical of turbulizer operation during cyclic pumping. Despite these concerns, the overall balance of corrosion resistance, manufacturability (including laser powder melting), and mechanical reliability makes the 316 L steel a preferred material over aluminum alloys, especially in high-abrasive loading conditions.

A comparative analysis with other researchers confirms the relevance and effectiveness of the approach used. For example, Fakher [44,45], in the review of the effectiveness of the rod pumps, cited data that showed that improvements in valve design and diagnostics reduced the failure rate by 15–20%. However, specific values for the ball rotation speed were not provided, which made our results (30 revolutions per 7 s) a unique indicator of the effectiveness of turbulent valve control.

The work of AC2T Research and UniLeoben [46] on the dynamics of valve ball movement led to the discovery of the phenomenon of “mid-cycle closing” and noted significant accelerations of up to 5–7 m/s² during closing. In our case, the stable rotation of the turbulizer removes some of these impact accelerations, which probably reduces the amplitude of water hammer and reduces excessive loads on the seat and ball. The rotation frequencies in our study demonstrate a controllable and predictable operating mode, whereas in the study described, the movement was chaotic and led to premature wear.

The frequency-elastic pump speed control technology described in Palka and Czyz [47] showed a 23% reduction in maximum impulse loads and an increase in overall efficiency from 24% to 38% at a speed of ~five strokes per minute (≈0.083 Hz). Our rotation rates (4.3 rpm) are significantly higher than the stroke frequency, indicating active vortex action within each stroke, creating additional lapping cycles and thus potentially increasing efficiency and reducing wear even in the absence of controlled frequency control.

The authors of [48,49] proposed upgrading valve assemblies to increase pump life. It mentioned the same approach of modifying the seat geometry and using turbulence, but without numerical data on ball rotation frequency. Our results complement this approach with specific figures that allow for estimating the potential resource efficiency.

In summary, a comparative analysis shows that our development is not just the addition of a vortex element, but a controlled hydrodynamic optimization that ensures surface lapping and slows valve wear. Numerical indicators of rotation frequency (4.3 rpm), reduction of flow asymmetry at the vertical axis, and relatively high resources in field conditions confirm the reliability and practical significance of the proposed design in comparison with existing approaches, which mainly operate with qualitative improvements without quantitative reference to valve dynamics. Moreover, further development of the valve assembly modeling may benefit from poroelastic formulations that account for nonhydrostatic in situ stress conditions and material anisotropy. Such an approach is particularly relevant when evaluating stress distribution and deformation behaviour in valve components operating under complex loading in subsurface environments. Fan et al. [50] presented a representative study, where poroelastic solutions were derived for a semipermeable borehole within transversely isotropic media under anisotropic stress conditions, providing valuable insights into stress transfer mechanisms in engineered subsurface systems.

The proposed valve assembly design with a turbulizer ensures uniform wear of the contact surfaces and extends the service life of the valves, and is technologically compatible with existing pumps. This makes the solution particularly attractive for use in mature oil fields with high water cut and the presence of mechanical impurities. Moreover, the experimental results clearly demonstrate that the durability of the turbulizer is materially dependent. The aluminum AL-Si-Mg alloy used in pilot tests could not withstand prolonged operation under high-solid-content flow conditions. The inner spiral plates suffered erosion, reducing the intended vortex effect. Switching to the 316 L stainless steel, with its superior hardness and corrosion resistance, is expected to mitigate such failures and enhance operational reliability. The results obtained allow recommending this design for further industrial application, provided that the durability of the turbulizers is increased through the use of more durable materials.

5. Conclusions

The results obtained during the work allow establishing a number of stable patterns demonstrating the influence of the turbulizer design on the rotation dynamics of the shut-off element and, as a consequence, on the wear resistance of the valve assembly. The most effective design in terms of forming a stable rotational movement of the ball was a turbulizer with a 7.5 mm wide spiral plate installed strictly along the axis of the valve channel. In this case, during the 7 s of valve opening, the ball made an average of 30 revolutions, which corresponds to a frequency of 4.29 rpm. Such rotation ensures a regular change in the contact area between the ball and the seat, which reduces the likelihood of local damage and contributes to more uniform wear of the surfaces. In other configurations with a spiral width of 5 mm and 10 mm, a decrease in the rotation frequency of up to 18–21 and 14–17 revolutions, respectively, was observed, which is explained by either insufficient or excessive impact on the flow. A 10° deviation of the channel axis from the vertical reduced the ball rotation by 22–25%, and by 35–40% at 15°, which indicates the high sensitivity of the vortex mechanism to flow symmetry.

Significant improvements were also recorded during field tests. The average service life of valves with a turbulizer was 75.3 days (SD = 9.6), which is 28% longer than that of standard designs (52.3 days). The rotation frequency (4.29 ± 0.31 rpm) and service life extension (75.3 ± 9.6 days) were statistically verified, and the improvements were found to be significant at p < 0.01. In some cases, the service life reached 101 days without repair, while the average service life of standard valves did not exceed 70 days. This confirms not only the reproducibility of the effect in the laboratory but also its stability under real operating conditions. Additional observation showed that the material of the turbulizer (AL-Si-Mg aluminum alloy) is not sufficiently resistant to abrasive effects in the presence of rust and sand in the liquid. This was the basis for switching to a more durable material, i.e., the 316 L stainless steel, which has a tensile strength of at least 485 MPa and a hardness of up to 217 HB. This transition may lead to a further increase in the service life of the unit and a reduction in the frequency of repairs.

The results obtained are of high practical significance. The design of the turbulizer is easily adaptable to serial pumps and can be implemented without changing the overall layout of the equipment. In conditions of mass application in a field of 900 wells, even an increase in the interval between repairs by 15–20 days can have a significant economic effect. Additional advantages include stabilisation of pump operation, reduction of accidents, reduction of reagent treatment volume, and reduction of unscheduled downtime.

The performed work reveals broad prospects for further research, including numerical modeling (CFD) of hydrodynamics in the internal volume of the valve, the development of new geometric solutions for turbulizers adapted to specific well operating conditions, as well as the use of wear-resistant alloys and composite materials. Particular attention should be paid to the numerical modeling of flows inside the modified valve design, since this will allow a deeper understanding of the nature of the interaction of the formed vortices with the shut-off element and optimizing the conditions of its rotation. In addition, the development of new-design solutions for turbulizers that take into account the specifics of wells (including a high level of mechanical impurities, temperature, and hydraulic conditions) will allow adapting the proposed solution to a wider range of operating situations.

One of the promising areas is the integration of digital twin technology of valve assemblies with pump monitoring systems. This will allow the implementation of predictive diagnostics of the technical condition of equipment based on the analysis of the rotation dynamics of the shut-off ball, comparing it with the accumulated wear statistics. This approach will increase reliability and allow for the advanced planning of maintenance. In addition, the proposed method for generating a controlled vortex flow inside the valve assembly demonstrates high efficiency and stability, making it a reliable tool for increasing the service life of equipment and reducing operating costs in oil production.

It is worth noting that the approach with inducing rotation of the shut-off element is applicable not only to sucker rod pumps, but can also be adapted to other types of lifting systems, such as screw and electric centrifugal pumps, especially in conditions of increased content of mechanical inclusions in the liquid. An additional area of development is the study of new materials for the manufacture of turbulizers, in particular, the use of hybrid and composite solutions with increased resistance to abrasive wear, which is especially important in aggressive environments. This will significantly increase the resource of the valve assembly with minimal costs for its improvement and implementation.

Scaling the proposed solution to the level of the entire field, where hundreds and even thousands of wells are operated, opens up significant opportunities for increasing energy efficiency, reducing unscheduled repairs, and reducing maintenance costs. This also helps to reduce the environmental impact by reducing the frequency of technological interventions and increasing the reliability of equipment, which is especially important in the context of the global transition to sustainable energy. Therefore, the results of this work not only demonstrate the practical efficiency of the proposed technical approach but also set the vector for its further scientific and industrial development.