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To address the problem of high adsorption of coalbed methane (CBM), a hydraulic cavitation tool for CBM production enhancement was designed based on the mechanism of cavitation wave promoting CBM production enhancement. To achieve the best cavitation performance and generate high-intensity cavitation waves to promote CBM desorption, the influence of inlet flow rate and upper and lower nozzle diameter ratio on cavitation performance was investigated by CFD technique and cavitation jet experiment. The simulation and experimental results show that as the inlet flow rate increases, the cavitation effect in the oscillation chamber increases, and the throttling pressure difference increases, so the throttling pressure difference is used to characterize the cavitation performance of the cavitation tool. The cavitation performance of the cavitation tool is analyzed when the upper and lower nozzle diameter ratio is from 1.5 to 3 and the inlet flow rate is from 2 to 10 m3/h. When the upper and lower nozzle diameter ratio is 2, the inlet flow rate is 6 m3/h, the throttling pressure difference increases by 73.2%, the value of vapor volume fraction increases by 77.7%, the cavitation effect no longer increases, achieving optimal cavitation performance. As a result, the high-intensity cavitation waves generated by the cavitation tool can continuously propagate in the formation, play a continuous oscillating effect on the coal seam, and can significantly increase the gas production of coalbed methane. The research results can provide new ideas for the development of CBM production enhancement tools. [ABSTRACT FROM AUTHOR]

The erosion wear of coiled tubing wound on the drum by fracturing fluid gravel greatly affects its service life and the operation safety during hydraulic jet fracturing operation in oilfield applications. Based on computational fluid dynamics, discrete phase model and optimal design theory, this paper uses ANSYS workbench software to numerically simulate the erosion of 2.375″ coiled tubing wound on the drum by fracturing fluid. The simulation result shows that the coiled tubing erosion rate is most affected by fracturing fluid injection velocity. Gravel mass flow rate has less effect. Gravel diameter has the least effect. Coiled tubing erosion wear can be effectively controlled by optimal matching smaller fracturing fluid injection velocity and a certain range of gravel mass flow rate values. This research provides a new simulation method for accurately and efficiently predicting coiled tubing erosion and wear failure, and the results can provide some theoretical help for fracturing operations. [ABSTRACT FROM AUTHOR]

With the development of gas well exploitation, the calculation of wellbore with single-phase state affected by single factor cannot meet the actual needs of engineering. We need to consider the simulation calculation of complex wellbore environment under the coupling of multiphase and multiple factors, so as to better serve the petroleum industry. In view of the problem that the commonly used temperature and pressure model can only be used for single-phase state under complex well conditions, and the error is large. Combined with the wellbore heat transfer mechanism and the calculation method of pipe flow pressure drop gradient, this study analyzes the shortcomings of Ramey model and Hassan & Kabir model through transient analysis. Based on the equations of mass conservation, momentum conservation and energy conservation, and considering the interaction between fluid physical parameters and temperature and pressure, the wellbore pressure coupling model of water-bearing gas well is established, and the Newton Raphael iterative method is used for MATLAB programming. On this basis, the relationship between tubing diameter, gas production, gas–water ratio, and wellbore temperature field and pressure field in high water-bearing gas wells is discussed. The results show that the wellbore temperature pressure coupling model of high water-bearing gas well considering the coupling of gas–liquid two-phase flow wellbore temperature pressure field has higher accuracy than Ramey model and Hassan & Kabir model, and the minimum coefficients of variation of each model are 0.022, 0.037 and 0.042, respectively. Therefore, the model in this study is highly consistent with the field measured data. Therefore, the findings of this study are helpful to better calculate the wellbore temperature and pressure parameters under complex well conditions. [ABSTRACT FROM AUTHOR]

In view of the failure causes of downhole choke fishing in tight gas wells, taking the choke fishing failure in Daning–Jixian block as representative, the failure causes are summarized through the actual fishing data and phenomena on site. This study analyzes from 11 aspects: (1) the influence of fishing time on throttle fishing; (2) the influence of the running depth of the choke on the fishing success rate of the choke; (3) the influence of gas well effusion on the success rate of choke fishing; (4) the influence of sand production on choke fishing; (5) the influence of restrictor structure on fishing success rate; (6) life analysis of restrictor; (7) type selection of throttle; (8) throttle structure design; (9) choke fishing; (10) choke sand blockage; (11) impact of switching well. This paper analyzes the methods to improve the fishing success rate of a choke and puts forward a reasonable solution to the fishing failure of choke, to ensure the safety of tight gas well construction. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the vibration characteristics of a geared rotor-bearing system (GRS) with a shaft crack. Firstly, a lateral–torsional coupling model is proposed. In the dynamic model, the rotating shafts of the GRS are modeled as Timoshenko beams; the meshing gear is modeled as a pair of rigid disks connected by a spring–damper with time-varying mesh stiffness; the opening and closing behavior of the crack is analyzed based on strain energy release rate theory and stress intensity factor theory. Then, this dynamic model is utilized to analyze the vibration characteristic of the GRS with a shaft crack. The results show that the most significant effect of a crack on the GRS is amplitude modulation of vibration signals. Not all the natural frequencies of the GRS can be affected by the crack. In addition, the feature frequencies of the GRS will also show some unique characteristics. This study provides a theoretical basis for the analysis and diagnosis of a GRS with a shaft crack. [ABSTRACT FROM AUTHOR]

In the process of fatigue loading, the segregation of solid solution elements makes dislocations continuously pile-up in ferrite lath to form subgrain, which improves the fatigue properties. In this study, the low cycle fatigue properties of two kinds of Cr-Mo tempered martensitic steels with different grain sizes were investigated at 350 °C. Then, the fracture morphology and the subgrain of ferrite lath were analyzed. The results show that the low cycle fatigue life of 90H steel is significantly higher than that of 80H steel, and a large number of secondary cracks are found in the fatigue fracture. The reason is that the segregation of solid solution atoms affects the dislocations movement during low cycle fatigue. And the finer lath subgrain structure of 90H steel makes it easier to occur in grain. Thus, the evolution process of subgrain structures is changed, and the crack propagation is hindered, resulting in a large number of secondary cracks, which improves the fatigue life. In addition, the segregation effect on fatigue life decreased with the strain amplitude increasing. [ABSTRACT FROM AUTHOR]

The downhole position of the throttle in natural gas well seriously affects the service life of the downhole throttle, and the incorrect down position will cause the downhole throttle cannot work. Therefore, it is important to study the optimal downhole depth of the throttle. The downhole throttle failure phenomenon of the natural gas well is serious in the Daning-Jixian region of China. The influence of downhole throttle depth on downhole throttle failure is analyzed in this area. By analyzing the mechanism of downhole throttling in the natural gas well and combining the coupling model of wellbore temperature and pressure, the optimal depth prediction model of downhole throttle is established. The comparison between the prediction results and the field construction results shows that: DJ 4-8 well 6, DJ 4-5 Well and DJ 4-10 well 2, the optimal throttle depths should be 1920 m, 1800 m, and 1950 m, respectively, but the actual depths on site are 2000 m, 1900 m, and 2200 m. There is a large deviation between the actual depths and optimal depths, causing the throttle to fail prematurely. According to this, obtaining the optimal downhole depth of the downhole throttle will ensure the working life of the downhole throttle and prevent the failure of the throttle. [ABSTRACT FROM AUTHOR]

The volcanic gas reservoir in Xushen gas field in the Northeast of China has the characteristic of low single-well production. Before gas wells are put into production, most of wells require fracturing transformation of the large sand amount and large displacement. Hence, an integrated fracturing and production string was developed. In the process of natural gas production, the integrated fracturing and production string is faced with the erosion caused by fracturing and CO2 corrosion. In order to ensure the safety of production, analysis and assessment of the dual effects of erosion and corrosion on the pipe string are required. The influence of the erosion angle, liquid velocity and sand ratio on the erosion rate of the integrated fracturing and production string was studied by using a self-made erosion experimental device and finally established the erosion rate prediction model; the samples of the tubing material after the erosion test were used in a high-temperature autoclave to carry out corrosion evaluation experiments to study the CO2 corrosion resistance of the tubing after erosion. The test results showed that severe corrosion occurred in the sample of P110 tubing after erosion, while slight corrosion occurred in the Super 13Cr tubing. On the basis of theoretical analysis results, the design and field construction of the integrated fracturing and production string are guided and ensured the safety of string in the whole life cycle. [ABSTRACT FROM AUTHOR]

Casing drilling has been recognized as a practical method to reduce drilling costs and avoid particular drill string problems that often occur in conventional drilling processes. To gain a better understanding of the whirling motion of rotating casing, the energy method was adopted to calculate the critical whirling speeds of casing for both pinned-pinned and fixed-fixed types of support. The calculated critical whirling speed of rotating casing for fixed-fixed supports was found to be 2.35 tunes than that of pinned-pinned supports. To observe the motion patterns of rotating casing in different cases, experiments were conducted in a transparent wellbore. Rotary speed and inclination angle were found to be the two main factors that affect the motion pattern of rotating casing. For the case of 300 gallons per minute (gpm) flow rate with annular fluid of water whirling motion was observed to initiate with a rotation speed of 120 rpm. Steady whirling motion was observed at ~155 rpm and higher With increasing inclination angles, whirling motion was found less likely to occur The backward whirling was not observed in the experiments because the friction between casing and simulated wellbore was not large enough. The variations of torque as a function of rotary speed at different flow rates, inclination angles, and rates of penetration (ROP) were also investigated, and the results were found useful for predicting the quality of borehole cleaning. It was shown that flow rate, inclination angle, and ROP have notable influence on the torque required to rotate casing. With increasing inclination angle, torque was found to increase and reach the maximum value at the horizontal position. For a given ROP, torque was found to decrease with increase in flow rate. For a given flow rate, torque was found to increase with increased ROP. [ABSTRACT FROM AUTHOR]

Integrated tubing can be used in the process of both fracturing and production for the oil and gas industry. During the process of fracturing, the inner surface of the tubing is subjected to the erosion from the slurry with sand and fracturing fluid, and then in the process of production, it is also corroded by the high-CO2-containing multiphase medium. To evaluate the CO2 corrosion resistance of Super 13Cr tubing after erosion in fracturing, the erosion test of Super 13Cr tubing under different impact angles was carried out by the jetting facility. For the samples with different erosion damage, the high-temperature and high-pressure CO2 corrosion experiments were carried out. The CO2 corrosion morphology with different erosion damage was also analyzed by SEM. The results show that different erosion damage at different impact angles can affect the corrosion rate in the later CO2 corrosion test. At an impact angle of 30°, the erosion damage is mainly caused by the cutting and plowing mechanisms by the eroded particles. The craters and folded extruded lips on the surface of the Super 13Cr tubing are formed and the passive film of super 13Cr is removed on the bottom of the craters, resulting in a corrosion rate that was approximately 1.4 times greater than that of the non-eroded surface. However, at the impact angle of 90°, the erosion mechanism is the plastic deformation and many platelets are formed. Less contact area between the fresh surface without passive film and the corrosive medium results in a lower corrosion rate than the material with 30° impact erosion damage. [ABSTRACT FROM AUTHOR]

In pump-starting and pump-stopping, because of the rapid change in fracturing fluid, the piping is subjected to water hammer effect. Water hammer effect results in severe vibration, which may damage the pipe or cause sealing failure of connections. To quantitatively analyze the water hammer effect and vibration characteristics in pump-starting and pump-stopping, the characterized lines method was adopted to analyze the velocities and dynamic pressures of fracturing fluid, as well as the axial velocities and additional stresses of piping at different depths. It shows that in pump-starting, the velocities and dynamic pressures of fracturing fluid as well as the axial velocities and additional stresses of piping increase greatly with increased flow rate of fracturing fluid. Meanwhile, the fluctuations of dynamic pressure and the axial velocities of piping decrease with increased depth. In the pump-stopping process, the shorter the pumping-stop time is, the higher the dynamic pressure of the fracturing fluid and the greater the axial velocity of the pipe. It is easier to damage the pipe in pump-stopping compared to pump-starting. The study provides a guidance of the flow rate of fracturing fluid, pump-starting time, and pump-stopping time to ensure safe fracturing. [ABSTRACT FROM AUTHOR]

Low-frequency vibration-bandgaps in elastic metamaterials open new possibilities to minimize low-frequency vibration and noise. Unfortunately, fabricating a complete vibration bandgap for low frequencies still represents a challenging engineering task. In this paper, a new type of a low-frequency complete vibration bandgap in a thin non-metal elastic metamaterial plate is introduced and investigated numerically. The proposed elastic metamaterial plate consists of decoupling-resonators, which are deposited on a 2D, locally resonant phononic-crystal plate, made of an array of rubber fillers, which are embedded in a nonmetallic plate. The dispersion relationship, the power-transmission spectrum, and the displacement fields for the eigenmode are calculated using the finite element method. It is shown that coupling between the local resonance mode of the decoupling-resonators and the Lamb-wave mode of the epoxy plate, consistent with the modal superposition principle, is responsible for the formation of vibration bandgaps. Moreover, the equivalent spring-mass system for the coupling-resonators can be decoupled by introducing a rubber filler. In addition, both longitudinal and the transverse elastic wave bandgaps can be tuned to the same low-frequency range. As a result, a novel kind of low-frequency complete vibration bandgap, which can damp a low-frequency elastic wave, is produced. Furthermore, the effects of the decoupling-resonators on the vibration bandgap are investigated. It is now possible that an elastic metamaterial plate can be dampen with complete low-frequency vibration bandgaps, which can potentially be used for commercial noise and vibration reduction. [ABSTRACT FROM AUTHOR]

An experimental study was conducted on erosion-corrosion (E-C) properties of 20Cr (Chinese steel grade) steel. Three corrosive solid-liquid two-phase aqueous solutions (distilled water, 3.5 wt.% NaCl aqueous solutions and saturated CO2 aqueous solutions, respectively, mixed with quartz grain) are used at three different experiments. The research confirmed that the E-C rate increased exponentially with the increase in flow velocity. The equation Ve = KVn can be used to express the relationship between E-C rate and flow velocity. Furthermore, a new regression approach called ‘segment fitting’ was proposed. It had better fitting precision to express the relationship between E-C rate and flow velocity. The analysis and SEM surface topography show that the material removal rate is controlled by electrochemical corrosion at lower flow velocity and may suffer from mechanically induced deterioration at higher flow velocity. The impact angle has complex effects on E-C rate. In the experiment condition, the E-C rate will reach highest at 45° impact angle. [ABSTRACT FROM AUTHOR]

Erosion damage is one of the main factors leading to failure of pipeline in oil field, especially for sudden contraction section under solid-liquid two-phase flow in hydraulic fracturing. In this article, a laboratory experiment was carried out to analyze the effects of pipe flow velocity, particle concentration and pipe inner diameter ratio on particle erosion of the reducing wall in high-viscosity liquid. The results show that the erosion rate and erosion distribution are different not only in radial direction but also in circumferential direction of the sample. The upper part of sample always has a minimum erosion rate and erosion area. Besides, the erosion rate of reducing wall is most affected by fluid flow velocity, and the erosion area is most sensitive to the change in the diameter ratio. Meanwhile, the erosion rate of reducing wall in cross-linked fracturing fluid is mainly determined by the fluid flowing state due to the high viscosity of the liquid. In general, the increase in flow velocity and diameter ratio not only causes the expansion of erosion-affected flow region in sudden contraction section, but also leads to more particles impact the wall. [ABSTRACT FROM AUTHOR]

A CFD-DEM-based two-phase flow model and a test-based erosion model are used to obtain the specific erosion on the reducing wall of sudden contraction section. The dimensionless filtered governing equations are adopted for incompressible power-law fluid flow, and the Hertz-Mindlin (no-slip) model for particle-particle and particle-wall contact. The annular reducing wall is divided into two erosion areas in radial direction based on erosion form and divided into four parts in the circumferential direction. The calculated result is verified with a full-scale experiment, and it shows a good agreement. The calculated results show that the erosion rate of the reducing wall is mainly determined by the flow velocity, and the erosion area is affected by liquid viscosity. The serious erosion region is located in the inner edge of the sample lower part, and this region expends to the outer circumference with the increasing flow velocity and the reducing liquid viscosity. The increase in flow velocity expands the flow region where the particle can impact the wall and thus increases the particle impact numbers. Graphical Abstract: [ABSTRACT FROM AUTHOR]