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Traditional static analysis cannot effectively explain the issue of the sealing performance of the premium connection being decreased due to the vibration of the tubing, leading to the failure of the connection sealing. In this paper, based on the energy dissipation theory and considering the influence of the micro contact slip of the sealing surface under the vibration of the tubing, a finite element model of the premium connection is established. The natural frequency and vibration mode are obtained through modal analysis experiments, and the accuracy of the finite element model is verified. The results show that the first five natural frequencies are mainly concentrated in the axial direction of the tubing, with the amplitude of the radial vibration mode being small. The vibration mode results are applied to the model as boundary conditions. It is found that an increase in the axial displacement amplitude leads to an increase in the energy dissipation of the sealing surface of the premium connection, which reduces the normal contact pressure and the effective length of the sealing surface, ultimately leading to a decrease in the sealing performance. [ABSTRACT FROM AUTHOR]

Injecting high-pressure fluid into a reservoir rock mass will change the mechanical properties of the rock; the strength and safety of a shale well wall are also extremely critical. In order to investigate the law of variation in water-sensitive shale strength during fracturing, an experimental study on the mechanical properties of shale under high confining pressure and water–rock coupling was carried out. Taking water-sensitive shale rock as the research object, the effects of high confining pressure and water content on the mechanical properties, residual strength, and macroscopic and microscopic failure modes of shale were analyzed. The test results show that the stress–strain curve of the shale gradually shortened with the decrease in the water content in the stage of void compaction and plastic yield, and the peak of the stress–strain curve was continuously enhanced. The water content and the peak intensity exhibited a negative linear correlation. The elastic modulus and water content showed an exponentially decreasing distribution. However, as the water content increased, the decreasing rate became slower, the softening coefficient increased, and the plastic deformation increased. The research results provide basic load parameters for the strength and safety of the casing of an oil layer under fracturing conditions. [ABSTRACT FROM AUTHOR]

To investigate corrosion and resulting changes in the sealing performance of premium connections in corrosive CO2 environments, we carried out a simulation analysis of their secondary current distribution and structural mechanics based on multi-physics field coupling. A finite element calculation model of Ф88.9 mm × 6.45 mm taper–taper premium connections (steel grade P110) was established using COMSOL6.0 general software. By analyzing corrosion laws under different environmental parameters, five internal pressures and tensile displacements were set. We simulated premium connections under different operating conditions using a secondary current distribution module. To investigate the distribution of the corrosion current density in premium connections under different operating conditions, the sealing performance before and after corrosion was quantitatively evaluated using a seal strength index. The results show that the current density is higher at the torque shoulder of the premium connections, which is more susceptible to damage. As the internal pressure increases, the current density in the inner wall of the column increases, and on the threads, the current density is highest at the rounded corners of the root of the thread, which is also more likely to be damaged. Under different internal pressures, although the sealing strength of the premium connections meets the sealing criterion, the corroded ones show a significant reduction in sealing performance. The results of this study provide a reliable theoretical basis for research on sealing premium connections in corrosive environments. [ABSTRACT FROM AUTHOR]

Casing pipes are used to support the wellbore of oil and gas wells so as to form complete wellbores. In some cases, these casing pipes suffer from manufacturing defects such as ovality, inner and outer wall eccentricity and microcracks, which lead to strength reduction. Therefore, it is necessary to analyze the residual strength of the sleeve with various manufacturing defects. According to the analysis formula of the anti-extrusion strength of casing pipe from the American Petroleum Institute (API), the diameter-thickness ratio was corrected accordingly taking into consideration of the difference in the diameter-thickness ratio caused by ovality and eccentricity, and the residual strength analysis formula of the defective casing was obtained. Taking the 127 mm x 7.52 mm P110 casing pipe as an example, the residual strength of the casing pipe was analyzed theoretically and numerically, and the residual strength of the casing pipes was compared and analyzed when the ellipticism deformation and the deviation degree of the center of the circle changed in the range of 1%-3%. The analysis shows that when the elliptonality and eccentricity are 3%, the residual strength of the casing is reduced by 6.81% and 7. 02%, respectively, the error is 1.91% and 2.04%, respectively, and the accuracy of the residual strength calculation formula meets the engineering requirements. When the microcracks of the same size are located in the inside, inner and outer walls of the pipe wall, the strength decreases by 8.51%, 3.55% and 4.69%, respectively. The strength of the microcracks decreases the most when the microcracks are located in the pipe wall, and the strength of the casing pipes decreases approximately linear with the increase of microcracks. According to the research, a quick reference chart of the residual strength of the casing pipes with different ovality and eccentricity was established, which was conductive to design and operation. The research results herein can provide not only a theoretical basis for the residual strength analysis of 127 mm x 7.52 mm P110 casing pipe with manufacturing defects, but also a new solution for the problem of cylinders with defects in elastic mechanics. [ABSTRACT FROM AUTHOR]

The premium connection is an important section of the tubing column. Under intricate downhole conditions, axial vibration generates alternating loads that cause energy dissipation between the sealing surfaces of the premium connection, reducing sealing performance. To investigate this issue, the mutual conversion process of sticking, slipping, and macroscopic slipping stages between the sealing surfaces of the premium connection under axial loads must be assessed. In this study, a finite element analysis model of a taper–taper Φ88.9 mm × 6.45 mm P110 premium connection is developed based on the discrete Iwan model's ontological relationship, and the sealing surface's force–displacement hysteresis curve is obtained. The equivalent Iwan model for this particular premium connection is constructed by discretizing the hysteresis curve and identifying the model's four sets of parameters. The correctness of the parameter identification method of the equivalent Iwan model is verified by comparing and analyzing the similarity of the two models. The energy dissipation in the sealing surfaces of the premium connection for different working conditions under dynamic loading is analyzed. This study reveals that the area similarity of the hysteresis curves of the two models is more than 92%, while the positional error is less than 2%. The sealing surface displacement amplitude of the premium connection is between 0.04 mm and 0.07 mm, while the sealing surface energy dissipation increases linearly, which may lead to a decline in sealing performance. [ABSTRACT FROM AUTHOR]

Periodic changes in wellbore temperature and pressure caused by the cyclic injecting and producing of gas storage wells affect wellbore integrity. To explore the distribution and influencing factors of wellbore temperature and pressure during gas storage well injection-production processes, based on energy conservation, momentum theorem, and the transient heat transfer mechanism of the wellbore, a temperature and pressure coupling model for gas storage injection-production wellbores was established, and a piecewise iterative method was used to solve the model equations. Compared with the field data, the predicted relative errors of the wellhead temperature and pressure were 2.30% and 2.07%, respectively, indicating that the coupling model has a high predictive accuracy. The influences of the injection-production conditions, tubing diameter, and overall heat transfer coefficient on the wellbore temperature and pressure distributions were analyzed through an example. When the gas injection flow rate increased by 1.5 times, the bottomhole temperature decreased by 37%. Doubling the overall heat transfer coefficient resulted in a 10% rise in the bottomhole temperature. An increase of 0.3 times in the gas injection pressure led to a 31% increase in bottomhole pressure. With a 1.5-fold increase in the gas production flow rate, the wellhead temperature rose by 28%, and the wellhead pressure dropped by 20%. The research in this paper can serve as a guide for the optimization design and safe operation of gas storage wells. [ABSTRACT FROM AUTHOR]

Considering the time-varying meshing stiffness and gear backlash, a dynamic model of gear transmission system is established. The Floquet theory is used to obtain the approximate analytic solution and the stability boundary curve of the transmission system. The Newmark-β numerical simulation method was used to simulate dynamic characteristics of gear system. The effect of time-varying mesh stiffness, backlash and damping effect on dynamic characteristics are studied. The results show that the system may generate parametric resonance when the frequency of parameter excitation is equal to 2/n of the free vibration period of the derived system;The gear backlash leads to multi-value properties and amplitude jump phenomena; The nonlinear vibration response of the system will be decreased with the increasing of the external excitation amplitude, damping ratio and the decreasing of the internal excitation amplitude.

This work addresses the ongoing challenge of optimizing sand control screens, attributed to a limited understanding of screen blocking. A novel one‐way computational fluid dynamics and discrete element method (CFD–DEM) coupling technique is presented to analyze the structural parameters of unconsolidated prepacked gravel screens (PPGS). CFD–DEM involves systematically investigating the width of the punched slot on the outer protective screen, the size of the gravel, and the efficiency of gravel packing to improve the antiblocking capability of unconsolidated PPGS. Results from numerical simulations reveal that under conditions of effective sand control, the amount of sand entering the gravel layer to the bridge (referred to as the sand pass rate) is positively correlated with the antilocking ability (referred to as oil productivity index) for unconsolidated PPGS. The efficiency of gravel packing has the most substantial effect on the antilocking performance of unconsolidated PPGS. The data suggest that appropriately reducing the efficiency of gravel packing can enhance the antilocking capability of unconsolidated PPGS. To design an unconsolidated PPGS with enhanced antilocking capability, the efficiency of gravel packing be determined first. Then, the gravel size is designed based on this efficiency, and the width relative to the gravel size is decided. This contemporary design principle diverges considerably from previous design principles for gravel‐packed sand control screens. Supporting validation experiments agree with simulation outcomes, suggesting the established one‐way CFD–DEM coupling method in this paper is suitable for analyzing the plugging mechanism of unconsolidated PPGS. Thus, the CFD–DEM coupling method improves the design of such screens for improved antiblocking performance. [ABSTRACT FROM AUTHOR]

The stresses and deformations of an eccentric cylindrical cam during the process of hydro-joining have been calculated in orthogonal curvilinear coordinates according to the mechanical model of the cam and governing equations in terms of appropriate complex potentials with suitable boundary conditions. The radial and shearing stress coefficients determined for an example cam are far less than that of the tangential stress during hydro-joining. The tangential stress coefficient of the outer surface of the cam is greater than that of the internal surface when the polar angle exceeds a particular value. The position of the maximum value of the radial stress coefficient is located on the internal surface of the cam, and the maximum shear stress coefficient is located between the inside and outside surfaces of the cam. The cam deformations on the internal and external surfaces under internal pressure respectively attain maximum values at particular angles. The maximum values of the radial and y-directional deformations are located at the position of the minimum wall thickness. The radial deformations determined for an example cam are far larger that the tangential deformations during hydro-joining. The errors between the theoretical and numerical solutions for the tangential stress and the y-directional deformation are both very small.

Corrosion medium such as CO2-Cl-causing corrosion pits in the pipe wall exist usually in the service environment of well tubing. These pits will become the fatigue source of the fatigue damage of oil tubing under cyclic loading. In this paper,tubing steel of 13 Cr used in oil well is selected as research object,and CO2-Cl- corrosive environment is selected for simulating the service condition of tubing. In the corrosive environment,fatigue experiments are performed on standard CT specimens to study crack propagation behavior of 13 Cr steel. Crack propagation rate of the 13 Cr steel under cyclic loading is measured in air environment,in Cl- environment and in CO2-Cl- corrosive environment respectively. The change of corrosion fatigue crack propagation rate under the three environment condition is carried out. With the observation of fracture morphology, the mechanism of corrosion fatigue failure of the 13 Cr steel in the CO2-Cl- corrosive environment is analyzed.