Study on Sealing Performance of Spring-Embedded Shoulder Protection Packer Rubber Cylinder

Abstract

Oil extraction is shifting towards high-temperature and high-pressure environments, which leads to the deterioration of the rubber material used in packer rubber cylinders, ultimately resulting in sealing failure. Hence, we propose enhancing the configuration of the rubber cylinder by incorporating a composite material consisting of metal and rubber. Additionally, we suggest integrating springs at the shoulders to fabricate a spring-embedded shoulder protection packer rubber cylinder. ABAQUS 2023 software was employed to simulate the packer setting process, investigating the variations in compression distance between a conventional packer rubber cylinder and a spring-embedded shoulder protection packer rubber cylinder. The results showed that at 25 °C and 177 °C, the compression distance of the fully seated spring-embedded shoulder protection packer rubber cylinder was reduced by 3% compared to the traditional packer rubber, Mises stress was reduced by 14%, and the sealing performance evaluation coefficient K of the rubber cylinder was increased by 2% to 10%.The stress in the spring-embedded shoulder protection packer rubber cylinder is primarily concentrated between the spring and the wire mesh, effectively ensuring the performance of the rubber cylinder and mitigating any potential decrease in sealing performance caused by internal stress concentration. The spring-embedded protective rubber cylinder will not experience shoulder protrusion during the sealing process. The incorporation of a spring-embedded shoulder protection mechanism in the packer rubber cylinder enhances the contact stress between the rubber cylinder and casing tube, mitigates stress concentration within the rubber cylinder, resolves shoulder protrusion issues, and ultimately improves both sealing performance and service life.

1. Introduction

The packer plays a vital role as a downhole tool in the oil extraction process, ensuring efficient oil extraction and facilitating the smooth operation of various downhole techniques. The rubber cylinder of the packer serves as its core component, effectively isolating the production layer and sealing the annulus [1]. Currently, oil extraction is typically carried out in environments characterized by high temperatures and pressures. The working conditions for rubber cylinders underground are extremely harsh, necessitating their ability to withstand external extreme conditions such as elevated temperature, increased pressure, and corrosive elements while functioning effectively underground over prolonged periods of time. Consequently, these conditions lead to a reduction in the elasticity and plasticity of the rubber cylinders under high pressure and temperature, ultimately resulting in seal failure. This would render the normal extraction of oil and gas from wells unfeasible, leading to significant economic losses [2].

Many scholars have proposed solutions to the problems of packer rubber cylinder failure in high-temperature and high-pressure underground wells, focusing on both the structure and material composition of the rubber cylinder. In terms of its structure, researchers have developed a three-layered rubber cylinder design that incorporates copper rings on the shoulders and utilizes different types of rubbers for each layer, effectively meeting operational requirements in extreme environments [3,4,5]. Zhang Fuying conducted a stability analysis that revealed that the influence of the height-to-diameter ratio on the stable deformation load of cylindrical rubber cylinders is relatively insignificant when compared to trapezoidal ring groove rubber cylinders and semi-circular ring groove rubber cylinders [6,7]. The influence of rubber material on the sealing performance of the packing element in a compression packer was analyzed through constitutive experiments. Constitutive models for three types of rubber materials were optimized based on the hyperelastic constitutive theory for rubber. A finite element model of the packing element system was established using the finite element method to investigate how different casing thicknesses and setting pressures affect the sealing performance of the packing element [8,9]. Pan Bo et al. used cold vulcanized adhesive to vulcanize the metal skeleton with an O-shaped circular cross section inside the rubber cylinder, avoiding shoulder protrusions at the upper and lower ends of the cylinder [10]. Cheng Ying et al. adopted a three-cylinder structure for the rubber cylinder, adding metal springs to the edge rubber cylinder to improve its stress and deformation, while increasing the chamfer at the end of the rubber cylinder to solve the sealing failure problem caused by rubber cylinder scraping during operation [11,12]. The packer comes with a hydraulic activation tool, enabling the installation of a multiport hydraulic fracturing liner in the well. Subsequently, the drill pipes can be disconnected and extracted from the well along with the hydraulic activation tool [13]. The results demonstrate a gradual decline in the mechanical properties of rubber with increasing temperature, pressure, and decompression velocity. Moreover, an elevated decompression velocity leads to the formation of small bubbles, large bubbles, and even bubble-cracking phenomena on the rubber surface, resulting in significantly compromised rubber sealing performance parameters [14]. The aforementioned enhancements to the rubber tube structure have significantly enhanced the sealing performance of the packer. However, with the gradual deepening of exploration and development, well depth as well as reservoir temperature and pressure continue to rise, posing greater challenges to exploration and development endeavors [15]. Therefore, commencing research on rubber materials serves as the most fundamental approach. Wang et al. improved the corrosion resistance of the rubber cylinder by improving its material, and the optimized packer rubber cylinder can meet the requirements of temperature resistance at 154 °C, pressure resistance at 79 MPa, and long-term effective sealing [16,17]. The optimized structural parameters are determined through the implementation of a genetic algorithm, resulting in a remarkable enhancement of 21% in the sealing performance. This research endeavor holds significant implications for augmenting the packer’s sealing capabilities and its adaptability to ultrahigh-pressure fracturing conditions encountered in deep shale gas wells [18]. Jin et al. conducted an analysis on the sealing performance of AFLAS and KALREZ, two rubber materials used in the production of packer rubber cylinders, and determined the optimal temperature range for sealing as well as the initial setting pressure range [19,20]. Oguzhan D et al. conducted a parametric analysis of the thermal performance of flat polypropylene pulsating heat pipes (PHPs) [21]. Türköz M et al. investigated the parameters affecting the sealing life of UHMWPE and PTFE in ultrahigh-pressure systems. Their results will contribute to the industrial design of sealing structures for ultrahigh pressures [22]. Shumao X showcased an adhesive’s adaptability and environmental resilience and the importance of coordination chemistry in developing reprogrammable hydrogels [23].

The aforementioned enhancements have significantly enhanced the sealing performance of the packer rubber cylinder. However, the issue of shoulder protrusion in high-temperature environments remains unresolved, leading to stress concentration within the rubber cylinder. Excessive stress concentration can result in seal failure of the rubber cylinder [24,25]. Therefore, it is proposed to integrate metal and rubber by designing a spring-embedded shoulder protection packer rubber cylinder to address both the problem of stress concentration and shoulder protrusion inside the rubber cylinder, thereby improving its sealing performance.

2. Structural Design of Spring-Embedded Shoulder Protection Packer Rubber Cylinder

In high-temperature and high-pressure environments, the performance of rubber materials deteriorates, rendering traditional packer rubber cylinders inadequate for meeting sealing requirements. Therefore, in consideration of a metal–rubber combination, a spring shoulder protection packer rubber cylinder has been designed. The spring-embedded shoulder protection packer rubber cylinder adopts a three-cylinder structure to provide substantial sealing pressure in both directions during the sealing process [26]. A multi-layer tensile spring is designed at the ends of the upper and lower rubber cylinders. However, this arrangement does not effectively allow the rubber cylinder to withstand large annular pressure differences during operation. When unsealing, the spring tension causes retraction of the rubber cylinder, effectively achieving unsealing while ensuring that the stretched spring acts as an anti-protrusion structure, preventing protrusion and flow of the rubber cylinder towards the annular space of the oil sleeve. This increases contact area and maintains contact stress, thereby preventing shoulder protrusion of the rubber cylinder. The stretching spring and rubber cylinder are filled with woven wire mesh that is fully vulcanized with rubber to form entirety. It is then placed in the upper part of the stretching spring to restrict the flow of weakened rubber material under high-temperature conditions, effectively filling gaps between wire diameters. The outer slant angle of the edge rubber cylinder is designed to be 30° in order to minimize stress concentration and reduce the likelihood of shoulder protrusion. A V-shaped groove is incorporated on both sides of the inner hole of the middle rubber cylinder, while a V-shaped groove is also added in the center of the outer circle to enhance its deformation and contraction capabilities. This design enables sufficient deformation of the middle rubber cylinder, resulting in increased contact stress and improved sealing performance of the packer. Thanks to its M-shaped overall structure, when unsealing, it facilitates retraction of the rubber cylinder back to its initial position, thereby facilitating repeated sealing and unsealing functions. A schematic diagram illustrating the structure of the rubber cylinder can be seen in Figure 1.

3. Analysis of Sealing Performance of Spring-Embedded Shoulder Protection Packer Rubber Cylinder

The rubber cylinder of the spring-embedded shoulder protection packer was analyzed using the finite element software package ABAQUS 2023. The influence of different setting loads on axial compression distance, Mises stress, contact stress, and sealing performance was analyzed by varying the applied load on the rubber cylinder.

3.1. Establishment of Finite Element Model for Rubber Cylinder

To investigate the stress situation of the packer rubber cylinder, a simplified research model consisting of upper and lower pressure rings, spacer rings, central pipes, edge rubber cylinders, middle rubber cylinders, and casings was established. A two-dimensional finite element model for spring-embedded shoulder protection rubber cylinder was developed, as shown in Figure 2, with structural parameters, presented in

Table 1. Related parameters—packer cartridge.

Name	Internal Diameter/mm	External Diameter/mm	Height/mm
Upper and lower pressure rings	105	147.8	27.2
Central tube	95	105	238.9
Spring	5.67	8.94
Upper and lower compression rings	105	145.5	6
Edge rubber cylinder	105	145.5	48.49
Medium rubber cylinder	105	145.5	75
Bushing	154.78	164.78	238.9

.

The packer rubber cylinder corresponding to the data in Table 1 is taken as the research object. The material of the compression ring, spacer ring, spring, and metal mesh is 20CrNiMo steel, with a density of 7.85 g/mm³, an elastic modulus of E = 2.08 × 10⁵ MPa, and a Poisson’s ratio of μ = 0.295. The central pipe and casing are simplified as rigid bodies for subsequent calculations. The Mooney–Rivlin model is a commonly used rubber constitutive model [27]. The traditional packer rubber cylinder uses rubber with IRHD = 90. Based on the Mooney–Rivlin two-parameter model, the stress–strain curve was measured through uniaxial tensile tests, and the material parameters were fitted as C₁₀ = 1.92556 MPa, C₀₁ = 0.96278 MPa, and Young’s modulus E = 17.33 MPa. The material properties weakened at 177 °C, with measured parameters of C₁₀ = 1.01555 MPa, C₀₁ = 0.50778 MPa, and Young’s modulus E = 9.14 MPa.

In terms of mesh division, the mesh of the upper and lower rubber cylinders is divided by free division: the mesh type is triangular and the mesh size is 1.5. The metal mesh in the side rubber cylinder is divided by free division: the mesh type is quadrilateral and the mesh size is 1. The middle rubber cylinder is divided by free division: the mesh type is triangular and the mesh size is 1.5. The upper and lower spacer rings and pressure rings are divided by free division: the mesh type is quadrilateral and the mesh size is 2. As for the setting of boundary conditions, the lower pressure ring is fixed in the XY direction and the upper and lower spacer ring in the X direction to prevent the spacer ring from moving left and right during the setting process. The reference point is set at the upper pressure ring and the load is applied in the Y direction of the reference point position.

3.2. Finite Element Analysis of Rubber Cylinder

3.2.1. Analysis of Axial Compression Distance of Rubber Cylinder

When conducting downhole operations, it is essential to apply an appropriate sealing load in order to effectively seal the rubber cylinder. Excessive sealing load can result in damage to the rubber cylinder, leading to seal failure, whereas insufficient seating load will prevent full compression of the rubber cylinder, resulting in an inability to isolate upper and lower layers. By utilizing finite element analysis, the compression distance between the spring-embedded shoulder packer rubber cylinder and the traditional packer rubber cylinder under a setting load of 110 kN at both 25 and 177 °C is calculate. Subsequently, the sealing performance of these two types of packer rubber cylinders was analyzed and compared.

An axial compression distance cloud map of the traditional packer rubber cylinder and the spring-embedded shoulder protection packer rubber cylinder under 25 °C and 177 °C temperatures is illustrated in Figure 3. As depicted, neither cylinder exhibits shoulder protrusions under 25 °C conditions. However, at 177 °C, the rubber material weakens, resulting in severe shoulder protrusions for the traditional packer rubber cylinder, while no such protrusions are observed for the spring-embedded shoulder protection packer rubber cylinder. By extracting compression distance data from both types of cylinders at 25 °C and 177 °C with a setting load ranging from 60 to 110 kN, axial compression distance relationship curves were plotted, as shown in Figure 4. Under the same sealing load, at 25 °C, the axial compression distance of the two types of rubber cylinders is the same.

At 177 °C, The percentage reduction in compression distance is calculated as follows:

$$L={\displaystyle \frac{L_a}{L_b}}-1$$

(1)

• where $L$—percentage of compression distance;
• $L_a$—traditional packer cartridge compression distance, mm;
• $L_b$—spring-embedded shoulder protection packer rubber cylinder compression distance, mm.

In this formula, the compression distance of the traditional packer casing at high temperature is $L_a$ = 46.85 mm, and the compression distance of the spring-embedded shoulder protection packer rubber cylinder is $L_b$ = 45.46. According to the above formula, a compression distance reduction percentage $L$ = 3% is obtained. This indicates that compared to traditional packer cartridges, the spring-embedded shoulder protection packer cartridge experiences less deformation after compression, has a longer contact length with the casing, and exhibits better sealing performance.

3.2.2. Mises Stress Analysis of Rubber Cylinder

A Mises stress cloud map of the traditional packer rubber cylinder and the spring-embedded shoulder protection packer rubber cylinder at both 25 °C and 177 °C is shown in Figure 5. As depicted, under 25 °C with a setting load of 110 kN, the maximum Mises stress of the spring-embedded shoulder protection packer rubber cylinder is comparable to that of the traditional packer rubber cylinder. However, stress concentration occurs at the spring and wire mesh in the case of the spring shoulder protection packer rubber cylinder, effectively safeguarding it against damage caused by stress concentration. Mises stress is used to extract data from cloud images, and the Mises stress reduction percentage is calculated as follows:

$$M={\displaystyle \frac{M_a}{M_b}}-1$$

(2)

• where $M$—Mises stress reduction percentage;
• $M_a$—the maximum Mises stress of conventional packer cartridge, MPa;
• $M_b$—the maximum Mises stress of spring shoulder packer cartridge, MPa.

The maximum Mises stress $M_a$ of traditional packer casing at high temperature was 37.58 MPa, the maximum Mises stress $M_b$ of spring shoulder packer casing was 32.68 MPa, and the maximum Mises stress reduction $M$ = 14% was obtained according to the above formula. While severe shoulder protrusion can be observed in the traditional packer rubber cylinder, no such issue arises for its spring-embedded shoulder protection variant, as stresses are concentrated solely within its spring area without any risk of tearing due to protrusion. Moreover, thanks to its wire mesh component, this design effectively prevents squeezing out of rubber material in high-temperature environments while also ensuring prolonged service life.

3.2.3. Analysis of Contact Stress between Spring-Embedded Shoulder Protection Packer Rubber Cylinder and Traditional Packer Rubber Cylinder on the Sleeve

The evaluation of the sealing performance of the packer cartridge relies heavily on contact stress, which is a crucial parameter. To investigate the distribution of contact stress between the spring-embedded shoulder protection packer rubber cylinder and the casing tube, contact stress data were extracted along the entire length of the rubber cylinder (from its upper edge to lower edge) at axial coordinates ranging from 0 to 152 mm under a setting load of 110 kN. Figure 6 plots the variations in contact stress between the rubber cylinder and casing for two types of packers along the longitudinal direction of the rubber cylinder. It can be observed from Figure 6 that both spring-embedded shoulder protection packer rubber cylinders and traditional packer rubber cylinders exhibit stress concentration phenomena. However, in the case of spring-embedded shoulder protection packer rubber cylinders, stress primarily concentrates around areas where springs and wire meshes are located, thereby reducing stress concentration within other parts of the rubber material itself. There is no shoulder protrusion phenomenon in the spring-embedded shoulder protection packer rubber cylinders, resulting in improved sealing performance by minimizing stress concentration on shoulders and extending overall service life.

3.2.4. Evaluation of Sealing Performance of Rubber Cylinder

The evaluation of the sealing performance of the spring-embedded shoulder protection packer rubber cylinder requires consideration not only of the contact stress between the rubber cylinder and the casing but also of the contact area and shoulder protrusion. To assess this sealing performance, an evaluation coefficient K is introduced based on the shoulder protrusion value J. A higher value of K indicates better sealing performance for the rubber cylinder [17].

$$K=C_{\mathrm{P}}\times C_{\mathrm{L}}$$

(3)

In the formula, C_P is the average contact stress between the rubber cylinder and the pipe wall (MPa) and C_L is the contact length between the rubber cylinder and the casing wall (mm).

The shoulder protrusion value is defined as the length of the annular space between the spacer and the wellbore along the axial direction after compression of the rubber cylinder, as illustrated in Figure 7 and Figure 8. This parameter serves as a standard for assessing the reliability of rubber cylinder sealing. A higher shoulder protrusion value indicates an increased risk of rubber cylinder damage.

After the packer has been set, extract the contact stress, contact length, and shoulder protrusion value between the spring-embedded shoulder protection packer rubber cylinder and the traditional packer rubber cylinder under a fully applied load of 110 kN. Subsequently, substitute these values into the aforementioned formula to calculate the sealing performance coefficient K value and shoulder protrusion value J between the rubber cylinder and casing wall, as illustrated in

Table 2. Calculation of K value for sealing performance coefficient of rubber cylinder and shoulder protrusion value J.

Name	CP/MPa	CL/mm	K	J/mm
Traditional packer rubber cylinder (25 °C)	3.49	104	362.96	1
Spring-embedded shoulder protection packer rubber cylinder (25 °C)	3.54	105	371.7	0
Traditional packer rubber cylinder (177 °C)	4.17	110	458.7	6
Spring-embedded shoulder protection packer rubber cylinder (177 °C)	4.48	114	510.72	0

.

The contact stress and contact length between the spring-embedded shoulder protection packer rubber cylinder and the casing wall are greater than those of the traditional packer rubber cylinder under both 25 °C and 177 °C, as indicated in Table 2. The sealing performance coefficient reduced by K percentage is calculated as follows:

$$K_M={\displaystyle \frac{K_a}{K_b}}-1$$

(4)

• where $K_M$—sealing performance factor K increases by percentage;
• $K_a$—sealing performance coefficient of spring shoulder packer rubber casing;
• $K_b$—sealing performance coefficient of traditional packer cartridge.

At 25 °C, the sealing performance coefficient $K_{a1}$ = 371.7 and the sealing performance coefficient $K_{b1}$ = 362.96. According to the above formula, the sealing performance coefficient increase percentage $K_{M1}$ = 2. At 177 °C, The sealing performance coefficient $K_{a2}$ = 371.7 for spring shoulder packer and $K_{b2}$ = 510.72 for traditional packer. The sealing performance coefficient increase percentage $K_{M2}$ = 11% was obtained according to the above formula. Compared to the traditional packer rubber cylinder, the K value is increased by 2% and 11%, while the shoulder protrusion value of the spring-embedded shoulder protection rubber cylinder remains at zero. Consequently, the sealing performance of the spring-embedded shoulder protection rubber cylinder surpasses that of its traditional counterpart.

4. Conclusions

A spring-embedded shoulder protection packer rubber cylinder is proposed to address the sealing failure of the packer cartridge in high-temperature environments. A finite element model is established for the spring-embedded shoulder protection packer rubber cylinder, and finite element simulations are conducted on both the spring-embedded shoulder protection packer rubber cylinder and traditional packer rubber cylinder. The effects of different temperatures and setting loads on axial compression distance, Mises stress, and contact stress between the two types of cylinders are analyzed. It can be concluded that at 25 °C and 177 °C, the compression distance of the spring-embedded shoulder protection packer rubber cylinder after complete sealing increases by 3% compared to traditional packer rubber cylinders. Additionally, compared with traditional packer rubber cylinder, the maximum Mises stress of the spring-embedded shoulder protection packer rubber cylinder is reduced by 14%, the sealing evaluation coefficient K of the rubber cylinder increases by 2% and 11%, and there is no longer any shoulder protrusion value observed, effectively solving this issue during rubber cylinder sealing. In contrast, when compared to traditional packer rubber cylinders, it can be concluded that the spring-embedded shoulder protection packer rubber cylinder exhibits better sealing performance and service life.