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Accurate control of natural gas flow and pressure is essential to achieving multi-gas combined production of the natural gas hydrates. In this study, a downhole stratification control tool for controlling natural gas flow rate and pressure with a multi-stage throttling structure was innovatively proposed. The multi-stage throttling structure combined an adjustable cage sleeve and a fixed nozzle. The numerical model of the internal flow field of the downhole stratification control tool was established. Through the computer fluid dynamics numerical simulation, the flow field change law inside the spool module of the downhole stratification control tool under different spool structures, different outlet pressures, and different spool openings was analyzed. Moreover, the spool module prototype was processed, and the indoor experiment of the spool's performance of reducing pressure and regulating production was carried out. The results show that the multi-stage throttling structure has the advantages of adjustable spool opening and moderate cooling range and the mass flow of gas inside the spool changes linearly with the opening of the spool. The spool module can accurately control the mass flow of natural gas under high-pressure conditions, and meet the needs of the downhole stratification control tool for accurate gas control. • A DSCT with multi-stage throttling structure is proposed. • The throttling structure composed of a cage sleeve and a fixed nozzle. • The flow field of multi-stage throttling structure is analyzed. • The DSCT can precisely control the gas mass flow under high-pressure conditions. • The pressure drop performance of the multi-stage throttling structure is the best. [ABSTRACT FROM AUTHOR]

The technology of TCP combined well testing is widely used in deepwater perforation and can cause string damage accidents. In order to improve the safety of the perforating string ANSYS/LS-DYNA software was used to analyze the influence of different parameters such as number of ammunition, tubing length, and the choice of perforation technology, on the tubing strength and deformation. Numerical simulation results show that the most vulnerable segment of the tubing is located at the bottom of the tube. The tubing length parameter can be effectively used to reduce the risk of tubing damage. The simulation model was verified by a field application case study. [ABSTRACT FROM AUTHOR]

• A 3D impact dynamic model of the perforated tubing string in curved well is developed. • In the model, the well trajectory, fluid pressure and interaction tool are taken into account comprehensively. • A similar experiment is carried out to demonstrate the accuracy of the model preliminarily. • The feasibility of the impact vibration model used in curved well is investigated through a case analysis. Perforating-test joint operation in oil&gas wells may causes strong impact vibration of downhole tools which can easily lead to buckling of tubing string, falling off of tools and damage of instruments. A 3D impact dynamic model of the perforated tubing string is established by using d'Alembert's principle and microelement method, and solved by the Newton difference method, taking into account the well trajectory, internal/external fluid pressure, interaction forces between the tubing and casing, and the coupling effect of perforating gun-shock absorber-tubing string. Due to the complexity of the verification, firstly, a similar experiment is carried out to test the accuracy of the model preliminarily. Secondly, through a case analysis, the feasibility of the model in the perforation impact dynamic analysis of tubing string in curved wells is further investigated. Both the two tests show that the model proposed in this paper has good calculation accuracy and can meet the needs of perforation shock vibration analysis of tubing string in curved wells perforation. [ABSTRACT FROM AUTHOR]

Long distance accumulators are widely used in underwater electro-hydraulic control systems. However, as the working depth increases, the underwater umbilical cable becomes longer. The actual physical properties of the gas in the accumulator change. These factors affect the charging characteristics of the accumulator. To address the above issues, a simulation model of the charging of the long distance accumulator under real operating conditions is developed. Among them, the real properties of the gas inside the accumulator were calculated using the Redlich–Kwong–Soave method. The coefficient of friction within the umbilical cable is based on the Reynolds number and relative roughness. The simulation data were compared with the experimental results in the South China Sea to verify the accuracy of the simulation model. The effects of key factors on the charging characteristics of the long distance accumulators were also analyzed. The results show that the simulation results are in good agreement with the experimental results. The law of accumulator charging was analyzed: the greater the pressure of the gas source, the smaller the accumulator charging time; the greater the working water depth, the shorter the accumulator charging time. The research provides guidance for the design of long distance accumulators. [ABSTRACT FROM AUTHOR]

Operation optimization of natural gas pipelines has received increasing attentions, due to such advantages as maximizing the operating economic benefit and the gas delivery amount. This paper provides a review on the most relevant research progress related to the steady-state operation optimization models of natural gas pipelines as well as corresponding solution methods based on stochastic optimization algorithms. The existing operation optimization model of the natural gas pipeline is a mixed-integer nonlinear programming (MINLP) model involving a nonconvex feasible region and mixing of continuous, discrete, and integer optimization variables, which represents an extremely difficult problem to be solved by use of optimization algorithms. A survey on the state of the art demonstrates that many stochastic algorithms show better performance of solving such optimization models due to their advantages of handling discrete variables and of high computation efficiency over classical deterministic optimization algorithms. The essential progress mainly with regard to the applications of the Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Ant Colony Optimization (ACO), Simulated Annealing (SA) algorithms, and their extensions is summarized. The performances of these algorithms are compared in terms of the quality of optimization results and the computation efficiency. Furthermore, the research challenges of improving the optimization model, enhancing the stochastic algorithms, developing an online optimization technology, researching the transient optimization, and studying operation optimization of the integrated energy network are discussed. [ABSTRACT FROM AUTHOR]

In the development of oil and gas fields, many wells have a phenomenon of wellhead growth originating in thermal stress of columns and cement sheaths poses severe challenges to shaft safety. Notably, the problem of wellhead growth is more serious in fully sealed oil and gas wells at sea. Therefore, this research on the wellbore cementation force, the wellbore lifting force, and wellhead growth for offshore oil and gas wells was critical. Based the effects on the comprehensive consideration of wellbore temperature change, annulus pressure, and performance parameters of cement sheath and casing, and then established the calculation method of cementing force, lifting force, and wellhead growth. Next, used the measured data and the data in the literature to validate the model. The results show that the calculation results of this model accord with the actual situation in the field. Finally, a gas well in the South China Sea was analyzed. Found that the increasing yield and annulus pressure will increase the height of wellhead growth, but the increasing thermal expansivity and the increasing elastic modulus of the cement sheath will decrease the height of wellhead growth. To avoid the wellhead growth, offshore oil and gas wells should adopt the submarine pipeline method (the height of the mud line relative to the deck was Zero). Thus, to improve the height of wellhead growth, the designed performance of the cement sheath, the management of annulus pressure, and the control of yield shall be introduced into the process of oil and gas field development. [ABSTRACT FROM AUTHOR]

The paper investigates the heat transfer in the exploitation of offshore argillaceous‐silt natural gas hydrate reservoirs considering sand control. The temperature prediction model is established in this investigation. The coupled pressure‐temperature model of the flowing fluid inside the wellbore is also presented. The sand control for argillaceous‐silt natural gas hydrate reservoirs mainly brings two effects into the temperature and pressure profiles simulation, including the moderate sand control and the Joule–Thompson effect. The moderate sand control is reflected by the volume and particle size of produced sand into the wellbore in the mathematical derivation. The Joule–Thompson is considered in the model due to the small diameter of sand control screens. The experiment is designed to measure the pressure drop caused by various mesh diameters of sand control screens. Subsequently, the regression relationship between the pressure drop and the mesh diameter is concluded to calculate the temperature change at the sand control screen. The simulation of heat transfer helps to analyze secondary hydrate formation risk in the wellbore. The proposed model identifies the high‐risk location of the secondary hydrate formation. The sand control effect and well geometry effect are discussed quantitatively. The strict sand control in the argillaceous‐silt natural gas hydrate (NGH) sediment exploitation reduces the risk of secondary hydrate formation significantly; however, it also has a negative effect on natural gas production. To balance the sand control and the prevention of secondary hydrate formation risk, it is suggested to install the heating electrode in the high‐risk location to ensure flow safety with acceptable sand control precision. The heat provided by heat electrodes is calculated by the model presented in this paper. The model can be used to determine the proper arrangement of heat electrodes. The paper also describes the secondary hydrate formation by adjusting the well geometry. The formation depth of the NGH reservoir and the sea interval should be considered in the risk analysis of the secondary hydrate formation. Additionally, the effects of wall thickness and wall thermal properties are evaluated and discussed. It is recommended to optimize the riser thickness with a small thermal conductivity value to minimize the secondary hydrate formation risk, which is more efficient compared to adjusting the cement sheath. [ABSTRACT FROM AUTHOR]

The weakly cemented mixture slurry which is formed by the natural gas hydrate (NGH) solid-state fluidization mining method that is composed of natural gas hydrate, sediment and water. The downhole cyclone of NGH needs to deal with such problems as high viscosity, narrow radial working space, and difficult to adjust the split ratio. Directly using the conventional solid-liquid cyclone structure for downhole sand removal cannot obtain good separation performance. And the conventional separator does not have a tubular structure suitable for solid fluidization exploitation of NGH. Therefore, in order to solve the problem of weak cementation between NGH and sediment due to large sand production during NGH exploitation, this study proposes a new method to separate weakly cemented natural gas hydrate based on the principle of spiral-cyclone coupling. And the model of spiral-cyclone separator was established. This method can break weakly cemented solid-phase particles in the slurry, and the effective separation and removal of ultra-fine sediment with cross-scale and micron size. The research also designs and optimizes the separation device for NGH sand removal. According to numerical simulation and theoretical analysis, the separation efficiency is greater than 60% when the particle size is larger than 5 µm and the inlet velocity is between 2 m/s and 10 m/s. The research results show that the proposed spiral-cyclone separation method has the characteristics of high separation efficiency, strong sand removal, and can break the cementation bond between the sediment and natural gas hydrate, which is a high-efficiency solid-liquid separation technology. • Spiral-cyclone separation principle revealed. • A novel method for separation weakly cemented NGH by spiral-cyclone principle. • The simulation model of spiral-cyclone separator was established. • The spiral-cyclone separator was optimized. • The separation process of NGH with spiral-cyclone separator was simulated. [ABSTRACT FROM AUTHOR]

This paper demonstrates the applicability of machine learning algorithms in sand production problems with natural gas hydrate (NGH)-bearing sands, which have been regarded as a grave concern for commercialization. The sanding problem hinders the commercial exploration of NGH reservoirs. The common sand production prediction methods need assumptions for complicated mathematical derivations. The main contribution of this paper was to introduce machine learning into the prediction sand production by using data from laboratory experiments. Four main machine learning algorithms were selected, namely, K-Nearest Neighbor, Support Vector Regression, Boosting Tree, and Multi-Layer Perceptron. Training datasets for machine learning were collected from a sand production experiment. The experiment considered both the geological parameters and the sand control effect. The machine learning algorithms were mainly evaluated according to their mean absolute error and coefficient of determination. The evaluation results showed that the most accurate results under the given conditions were from the Boosting Tree algorithm, while the K-Nearest Neighbor had the worst prediction performance. Considering an ensemble prediction model, the Support Vector Regression and Multi-Layer Perceptron could also be applied for the prediction of sand production. The tuning process revealed that the Gaussian kernel was the proper kernel function for improving the prediction performance of SVR. In addition, the best parameters for both the Boosting Tree and Multi-Layer Perceptron were recommended for the accurate prediction of sand production. This paper also involved one case study to compare the prediction results of the machine learning models and classic numerical simulation, which showed the capability of machine learning of accurately predicting sand production, especially under stable pressure conditions. [ABSTRACT FROM AUTHOR]

• The nonlinear dynamic models of riser under different suspension evacuation conditions are established. • The nonlinearity of the model takes into account the actual configuration of riser, VIV in cross-flow (CF) and in-line (IL) directions, and large deformation. • Experiments are designed and carried out to verify the nonlinear model. • The vibration frequency and mode shape of riser under different influence factors are analyzed. This paper establishes a nonlinear dynamic model for a suspended riser under the condition of considering realistic configurations, based on the principles of virtual work and Hamilton's variational principle. The nonlinearity of the model is manifested by considering vortex-induced vibration in the cross flow (CF) and in-line (IL) directions, as well as large deformations, taking into account the variable diameter of the riser in the compliant riser system. The model is discretized using the finite element method and solved using the Newmark-β method. Experimental validation is conducted to verify the effectiveness of the model. Utilizing the parameters of a riser in a well in the South China Sea, the paper explores the influence of different environmental and structural parameters on the VIV response characteristics of a compliant riser. Results show that the vibration frequency is controlled by both the bare tube and buoyant block when the buoyant block coverage rate is 25%, which can significantly inhibit VIV. With the increase of flow velocity, the VIV energy jumps from low order to high order, and the riser mode also transitions from low order to high order. The increase in suspension length transfers the vibration energy from high to low frequency, thus realizing energy transition and mode shape transformation. With the increase in LMRP weight, the vibration and natural frequencies of the riser increase synchronously, the vibration amplitude decreases, and the mode shape remains unchanged. [ABSTRACT FROM AUTHOR]

As the natural gas hydrate (NGH) resources show a bright future, more and more commercial and technical focuses have been devoted to this area. The low productivity, the sanding problem, and the poor economic performance are vital problems hindering the long‐term commercial exploration and development of NGS sediments. Among all these problems, the sanding problem can aggravate the low productivity and the poor economic efficiency problems. Therefore, it is necessary to investigate and tackle the sanding problem for the safe, long‐term, and large‐scale commercial development of offshore NGH resources. The sanding problem of the NGH sediment is highly related to the mechanical behavior of sediment. The main influencing factors are discussed, which are hydrate saturation, effective confining pressure, sand content, hydrate distribution, and multiple‐physical fields. This article summarizes the current research achievements systematically to determine how these factors affect sand production in NGH sediments. Besides the macrolevel about mechanical behaviors of NGH sediment, the sand motion modeling is also included in this review. The source of sand production is the free‐moving sand which comes from formation deformation. The review compares most commonly used yield criteria and then recommends a proper one for NGH sediments. The paper subsequently discusses the common investigation methods for the sanding problem in this area, including numerical simulation and experiments. The design and effect of sand control techniques have also been reviewed and discussed. According to the review results, the paper concludes the current research drawbacks and generates suggestions for future research. The novel methods of sand control investigation are machine learning and optimization methods. [ABSTRACT FROM AUTHOR]

In deep-water drilling for oil and gas, the annular blowout preventer (BOP) is subjected to sustained high pressure or impact loads, causing the concentration of stress in some regions, which can easily cause cracks or fatigue damage. The top cover and housing of the annular BOP are the main pressure-containing parts. Once they fail during the emergency shut-in process, a blowout accident will occur, and there may be casualties and major economic losses. Therefore, the stress concentration regions of the top cover and the housing must be analysed to ensure safe operation. In this study, a high-fidelity approach to monitor the stress was established. This approach combines the theoretical calculation method (TCM), finite-element analysis (FEA) and stress testing experiment (STE). The stress distribution laws of the top cover and housing were measured under the rated working pressure and hydrostatic test pressure. The results indicated that the TCM, FEA, and STE exhibited the same curve trend of stress. Moreover, the FEA results were almost identical to the STE results for the stress values of testing points. The FEA results indicated that there were two critical stress regions in the housing. These were regions where cracks and failures had actually occurred in the past. The main technical contribution of the study is that it may serve as the basis for additional investigations into abandonment evaluation, fatigue analysis, and residual life evaluation. • A high-fidelity approach combining theoretical calculation method, finite element analysis and stress testing experiment. • The stress distribution laws under rated working pressure and hydrostatic test pressure were analysed. • Two critical stress regions of annular blowout preventer were determined. [ABSTRACT FROM AUTHOR]

Intelligent wells equipped with the interval control valve (ICV), which have the potential applications to significantly improve oil production or control the water production of wells and fields, are more and more widely utilized in the oilfields. The radial metal seal of an ICV is intended to isolate the flow of produced fluids between the casing annulus and the well tubing. The contact mechanical behaviors of the radial metal seal are essential to the structural design and reliability of ICVs in the intelligent well. In this paper, the two‐dimensional axisymmetric assembly of the radial metal seal and the closure member is abstracted as a combination of interference fit model and cantilever beam model. Based on that, the related theoretical model, between the radial metal seal's contact stress and its independent variables, has been derived. Next, numerically simulations of contact stress between the radial metal seal and the closure member for different independent variables are conducted by the finite element method (FEM) to validate the theoretical model. It is found that the mean absolute value of relative error between the numerical and theoretical results of the contact stress is approximately 10%. Additionally, the structural parameters of the radial metal seal are proposed with the absolute value of relative error <10%. Furthermore, the value of the contact stress based on the cantilever beam model can be used to calculate an approximation theoretical solution. In summary, the proposed theoretical model provides a foundation for the design, improvement, and selection of radial metal seal under the known oilfield conditions. [ABSTRACT FROM AUTHOR]

This work studied the effects of nano-SiO2 addition in drilling fluid on the wear behavior of casing. The disc specimens and pin specimens were made of 2Cr13 steel and G105 steel, respectively, and the water-based drilling fluids added with different amount of nano-SiO2 were tested, based on which, the wear rate, surface morphology, surface profile, and composition of the wear product were analyzed. Results showed that, the main wear mechanism of 2Cr13 steel casing in the drilling fluid is abrasive–corrosive wear. Adding nano-SiO2 to the drilling fluid can significantly reduce the casing wear. As the nano-SiO2 concentration increases, the wear rate and mean friction coefficient both increase first and then decrease. Drilling fluid shows best lubrication performance when the nano-SiO2 concentration is 2%. The shielding effect of nano-SiO2 can slow down the vicious cycle of “oxidation–destruction–reoxidation” during the wear process. Microhardness of tribofilms increases when adding more nano-SiO2 into drilling fluid, which increases the wear resistance of disc surfaces. However, the excessive addition of nano-SiO2 on a 2% concentration basis can lead to the decrease in bonding strength between tribofilms and matrix, leading to large delamination on the disc surface and therefore reducing the shielding effect of nano-SiO2. [ABSTRACT FROM AUTHOR]

Annular pressure buildup (APB) is induced by high‐temperature tubing fluid heating the trapped annular fluid, which leads to liquid thermal expansion at the production stage in deepwater wells. Casing would be burst or collapsed without APB mitigation. A novel recovery relief method was adopted to mitigate APB through the principle of differential pressure. To assess the application effect of the method, APB prediction model and pressure relief threshold determination method were proposed, where the transient heat transfer and volume and pressure coupling were involved. The laboratory test of the principle prototype was conducted so that the feasibility of the recovery relief method was validated. The numerical APB mitigation effect was simulated by the field example. The production simulation results indicated that the high‐temperature‐induced APB caused casing failure. The simulation of APB mitigation with both inward and outward directions demonstrated that the casings using outward mitigation method were safer with lower safe factor. Besides, comparing the mitigating effect to the rupture disk, the recovery relief method had more maximum allowable APB of annulus A. Additionally, compared to other 11 ordinary mitigation methods with the qualities of engineering reliability, technology feasibility, and economy, the recovery relief method had best mitigation performance. Therefore, the recovery relief method was recommended for APB mitigating practice. [ABSTRACT FROM AUTHOR]

Asset Integrity Management (AIM) technology has been rapidly developed and applied so that it has become a main management technology of offshore platform equipment and facilities. Risk identification and quantitative evaluation method is one of the core contents in the AIM. However, most of the existing methods are qualitative analysis results, simple analysis process, and strong subjectivity, which can no longer meet the development of AIM technology system. By analyzing disadvantages and shortcomings of the existing methods and adapting to the technology requirements of the AIM, a Streamline Failure Mode Effects and Criticality Analysis (SFMECA) was presented to achieve risk identification and quantitative evaluation based on the traditional FMECA and Borda scoring method. Taking a truss crane as a case study, feasibility and operability of the SFMECA were verified effectively with obtaining a detailed and complete analysis worksheet. Compared with their analysis process and worksheet, it was more specific, more comprehensive, and more operable by applying the SFMECA than the traditional FMECA. Moreover, in the SFMECA, failure risk was divided into four categories in detail and quantified separately to better distinguish and evaluate failure effect. Then a comprehensive quantitative evaluation method of four risks was carried out and risk knots in risk priority number (RPN) were obviously reduced, which help to develop more accurate risk management measures. Independent evaluation mechanism of multiple experts or teams is adopted in the SFMECA to make the analysis and evaluation results more objective. So the worksheet obtained through the SFMECA contains more quantitative data, comprehensive information, and objective results, which can better meet technical system of the AIM. Therefore, application of the SFMECA can provide technical support for extension and application of the AIM technology, including risk quantitative analysis, maintenance decision, and integrity evaluation, for offshore platform equipment and facilities. [ABSTRACT FROM AUTHOR]

A model is developed to investigate the dynamic behavior of a deepwater drilling platform riser system under emergency evacuation conditions. In the model, the riser in the ocean environment is modeled as a beam with coupled transverse and axial motions, and its upper and lower ends are respectively connected to the platform and to the lower marine riser package with hard joints. The fluid forces and the added mass and drag forces are modeled using a semi-empirical Morison equation, so the equations of the model are nonlinear, coupled, and multibody. The model is discretized in a finite element approach and solved using Newmark's method. Its validity is verified using ANSYS. Using the model, the influences of platform motion, riser suspension length, ocean load, and platform evacuation speed on the dynamic behavior of the riser are determined, and the results can provide theoretical support for the design and practical operation of hard suspension pipe strings. [ABSTRACT FROM AUTHOR]

Accurate acquisition of permeability change in hydrate-bearing sediments (HBSs) is the key to predicting reservoirs' multiphase fluids distribution and production capacity. Hydrate saturation and effective stress present significant effects on reservoir permeability. Thus, the influence of hydrate saturation and effective stress on gas permeability change of remolded core during decompression was studied. The results showed that effective stress compression and hydrate decomposition determine the flow channel structure within hydrate sediments. Under unconsolidated and low effective stress(σ' = 1.2 MPa) conditions, the gas permeability increased gradually as the decomposition of hydrate, and the magnitude of permeability variation before and after decomposition increased with increasing hydrate saturation, indicating that the effect of hydrate saturation on permeability dynamic change dominated at low effective stresses. When σ′ was increased to 3.2 MPa and 5.2 MPa, the results were contrary, indicating that the effective stress variation on gas permeability dynamic change dominated at higher effective stresses. In addition, it was found that compression led to higher heat transfer efficiency in high-saturation samples. When hydrate saturation was increased from 23.37% to 48.7%, the effect of increasing effective stress on gas production changed from inhibition to facilitation. • Hydrate and effective stress affect the permeability variation paths. • Effective stress affects the factor that dominates the permeability variation. • Hydrate saturation causes significant effects on permeability damage rate. • The effect of effective stress on gas production is affected by hydrate. [ABSTRACT FROM AUTHOR]

The successful offshore hydrate production tests in the South China Sea proved the high productivity of clayey-silty hydrate reservoirs. However, the mechanical characteristics of these clayey-silty sediments have not been comprehensively investigated since the concerns about the productivity of such low-permeability reservoirs. In this study, based on the sediment matrix from the South China Sea, specimens were remolded with a porosity of 41% and hydrate saturation of 30% to perform a comprehensive mechanical investigation from micro to macro. Microcosmically, the hydrate in the clayey-silty sediment presents patchy distribution, being particle-displacive and particle-wrapped segregated hydrate morphology. Macroscopically, the compression and swelling indices of hydrate-bearing sediments in the South China Sea are obtained for the first time, which are larger than that of the hydrate reservoir in Krishna-Godavari Basin. The increasing effective confining pressure can slightly reduce the strain-softening and dilation characteristics of the hydrate-bearing sediments in the South China Sea. What's more, the failure strength and stiffness increase with an increasing effective confining pressure, while the failure volumetric strain firstly increases and subsequently decreases with an increasing effective confining pressure. These results are essential input parameters to establish a constitutive model and numerical simulations. • Hydrate presents particle-displacive and particle-wrapped in the clayey silt. • The compression and swelling indexes of hydrate reservoir in the South China Sea are obtained for the first time. • Increasing burial depth can reduce the strain-softening and dilation of the hydrate reservoir in the South China Sea. [ABSTRACT FROM AUTHOR]

Subsea test tree (SSTT) is an essential safety device for the completion testing operations of deepwater extraction of oil, natural gas, and natural gas hydrate. During the implementation of the emergency release procedure of the SSTT, the coiled tubing or steel wire running in it must be quickly and effectively sheared by its ball valve mechanism. Therefore, clearly revealing the shearing mechanism and accurately evaluating the shearing performance of the ball valve mechanism is essential for maximizing the safety performance of SSTT operation. The finite element numerical simulation method established a dynamic shear model of the SSTT's ball valve under different working conditions and structural parameters to clarify the influencing factors and laws of the ball valve shearing performance. The results of numerical simulation model agree well with the laboratory tests, verifying the scientific validity and accuracy of the numerical simulation method and the generated model. Further, the SSTT's shearing process under different working conditions and geometry was calculated based on the method and model mentioned above. It shows that the tension of coiled tubing is greater, the required of shear moment is smaller. The internal pressure lead to more difficult shearing conditions. In the eccentric position, the ball valve was subjected to a reaction force moment perpendicular to the rotation direction of the ball valve. The larger the ball valve diameter, the shear force required to shear coiled tubing. The SSTT upper seat Angle also affects shear failure performance, and coiled tubing can be shear at 10°, 30°, and 40° with less shear moment. The minimum shear moment is required when the edge of the shearing ball valve has a 1.5 mm circular chamfering. This study proposes an optimization method to improve the shear fracture performance of ball valves. Moreover, this study provides essential guidelines for the optimal design and application operation on the SSTT's ball-valve mechanism. [Display omitted] • A dynamic simulation method of ball valve shearing is proposed and verified. • The dynamic simulation results are consistent with the experimental results. • The influence of ball valve on shear fracture performance is revealed. • An optimization method of ball valve is presented to improve shear fracture performance. [ABSTRACT FROM AUTHOR]

• A dynamic model for drilling risers under soft suspension evacuation is established. • The nonlinear coupling of longitudinal-CF-IL in three directions is considered. • The correctness and effectiveness of model are verified by experimental results. • The progressiveness of model is verified by comparing with the hard suspension model. • The effect of environmental and operation parameters on response characteristics are investigated. In order to provide theoretical reference for the design and operation of soft suspension riser, firstly, a three-dimensional nonlinear vibration model of risers is established using the Hamilton variation and virtual work principles. In the model, three main nonlinear factors were taken into account: longitudinal-lateral (LG/LT) coupling vibration, vortex induced vibration (VIV) and large deformation. The finite element method (FEM) is used to realize the numerical solution of the nonlinear vibration model. Secondly, the correctness and effectiveness of the nonlinear vibration model is verified by the experimental measured data and ANSYS software. The progressiveness of the model is verified by comparing with the uncoupled model and hard suspension, and it demonstrate that, the proposed model can reflect the high nonlinearity of the riser system and describe the nonlinear vibration of the real riser more accurately. The natural frequency of the nonlinear model was much higher and the modal response more complex. The nonlinear coupling effects increase the vibration amplitude in the cross flow (CF) direction and the in-line (IL) direction. Thirdly, the model was used to analyze the effects of structure parameters, environmental parameters and operation parameters on the response characteristics of soft suspension evacuation riser. Some important phenomena have been found: reasonable allocation rate of buoyancy block can effectively restrain the vibration of riser. The optimal allocation rate of buoyancy block is related to the riser structure and operation conditions, which can be determined using proposed nonlinear model. Meanwhile, it is necessary to evacuate along the flow direction as much as possible, with an evacuation speed of lower than 1 m/s. [ABSTRACT FROM AUTHOR]

• An orthogonal wear experiment was performed on the 13Cr-L80 tubing string. • The wear patterns of the tubing-casing were primarily abrasive and adhesive wears. • The wear life can be augmented by reducing contact load and vibration displacement. • The vibration frequency of tubing string should be maintained below 1.5 Hz. • The completion fluid should be set as approximately 1.2 g/cm3 on-site. Due to wear failures caused by tubing string vibrations in high-yield gas wells, an orthogonal wear experiment was performed on the 13Cr-L80 tubing string. The influence of contact load, friction frequency, wear time, completion fluid density, and reciprocating stroke length on the wear characteristics of the tubing string were effectively analyzed using range analysis, variance analysis and the control variable methods. The results demonstrate that, the wear patterns of the tubing-casing were primarily abrasive and adhesive wears, with minimal corrosion wear. In-field operations, the service life of the tubing string in high-yield gas wells can be effectively augmented by reducing the contact load and longitudinal vibration displacement of the tubing-casing, maintaining the vibration frequency of the tubing string below 1.5 Hz, and utilizing a completion fluid with a higher density (approximately 1.2 g/cm3). The wear amount and friction coefficient of the tubing string are primarily influenced by the contact load and reciprocating stroke length, respectively. Moreover, the effect significances of the contact load and reciprocating stroke length were particularly significant and significant, respectively. These results provide useful guidance for designing and implementing approaches to improve the service life of tubing strings in high-yield gas wells. [ABSTRACT FROM AUTHOR]

• A nonlinear FIV model of tubing string in HPHT oil&gas wells was established and verified by similar experiment. • The production allocation should be far away from the mutation value which can be determined using the FIV model. • In well trajectory design, the length of vertical section should be reduced, the length of building section and the inclination angle should be increased. • The optimal position of the packer can be determined using the FIV method to guide the design of it. This study has established a nonlinear flow-induced vibration (FIV) model of tubing string by using the micro-element method and energy method with the Hamiltonian variational principle, in order to address the vibration failure problem of the tubing string induced by high-speed fluid flow in the tubing of high temperature and high pressure (HPHT) oil&gas well. This model considered factors such as borehole trajectory changes, wellbore temperature and pressure variations, self-weight of the tubing string, and the contact-impact of the tubing-casing. Based on the structural parameters of the M high-yield gas well in the South China Sea, a simulation experiment of the tubing string vibration was conducted according to the similarity principle. A comparison between the experiment data and theoretical data showed that the calculation accuracy exceeded 84%, which verified the correctness and validity of the nonlinear vibration model established in this study. On this basis, the influence of the production rate, well inclination angle, well section length, and packer position on the vibration response characteristics of the tubing string were analyzed systematically. It was found that: ①with the increase of the production rate, the vibration response of the tubing string became clearer. The production rate interval that showed abrupt changes was from 0.9 ~1.2 million m3/day. Thus, during designing, such production rate intervals with abrupt changes should be avoided to ensure the safe usage of the tubing strings; ②with the increase of the well inclination angle, the vibration response of the tubing string decreased to a certain extent. Regarding the influence of the well section length, the longitudinal vibration response of the tubing string was most sensitive to the length of the vertical section, followed by the steady inclined section, and finally the angle building section. Thus, during designing, the length of the vertical section should be reduced, while the length of the angle building section and the well inclination angle of the steady inclined section should be increased; ③As the position of the production packer moved up, the vibration responses of the lower and middle tubing strings both decreased, and the optimal packer position was between 3,549 and 3,666 m. The research results can serve as an effective analysis tool and provide a theoretical basis for the safety design of the tubing strings in the HPHT oil&gas well site. [ABSTRACT FROM AUTHOR]

This work investigated the effects of sliding speed on tribological behavior of AA 7075 petroleum casing in simulated drilling environment by pin-on-disc wear test. The main wear mechanism of AA 7075 disc at low sliding speed (0.0628 m/s and 0.157 m/s) was abrasive wear and oxidative wear at middle sliding speed (0.314 m/s). As sliding speed increases to higher sliding speed (0.471 m/s and 0.628 m/s), adhesive delamination wear dominated the wear process. The tribo oxides layer can efficiently protected the alloy substrate only at sliding speed of 0.314 m/s. At higher sliding speeds, tribo oxides layer were removed quickly once it was formed due to its internal fractures of tribo oxides and lower bonging strength with substrate. • Effects of sliding speed on tribological behavior of AA 7075 oil casing are presented. • Best wear resistance of AA 7075 was observed at sliding speed of 0.314 m/s. • The performance of tribo oxides layers is the key point of wear mechanism transition. • Tribo oxides layer are formed and removed rapidly at a higher sliding speed. [ABSTRACT FROM AUTHOR]

A dynamic analysis model for the drilling riser was established and applied under normal drilling and hang-off conditions by distinguishing the boundary condition. This model was discretized by the FEM and solved by Newmark β method. The correctness of this model was verified through an experiment. Results indicate that the lateral displacement distribution and riser stress increase with the current speed and platform drift distance. A platform that drifts along the current is conducive to counteract the rotation of the upper joint but promotes the rotation of the bottom joint of the riser. A riser that is approximately 2,000 m long under normal drilling condition can withstand the current loads for a 10-year return period. The hang-off riser should be evacuated after being disconnected from the bottom along with the current as soon as possible. In addition, the riser that evacuated under soft hang-off condition can significantly reduce stress but enlarge the rotation angle of the upper flexible joint. Image 1 • Established a unified analysis model of deep water riser considering normal drilling and hang-off conditions. • The analysis model is discretized by finite element method and solved via Newmark β method. • Verified the model by conducting a similar experiment in a deep-water basin. • Discussed the dynamic mechanical behavior and safety of riser under different working conditions and loads. [ABSTRACT FROM AUTHOR]