The high-pressure, low-temperature environment prevailing in offshore gas production and transportation is prone to forming methane hydrates inside the tubings or pipelines, resulting in reduced production and flow assurance problems. Conventional hydrate prevention relies on the continuous injection of chemicals to alter the chemical potential of the mixture stream. Such a method has the disadvantages of high cost, high toxicity, and high environmental impact. Effective hydrate prevention methods are urgently needed in offshore petroleum engineering. When fluid in nozzles or near turbine blades experiences an abrupt pressure drop, cavitation bubbles form and accumulate in the fluid. Bubbles collapse as they move downstream along the flow. As the bubble collapse, extremely high temperature and high pressure are generated, and the ambient fluid around the bubble is heated. In this paper, the thermal effect of cavitation is introduced into methane hydrate prevention. A numerical simulation of cavitation inside an injector was performed, an experimental setup was established, and the influences of various working parameters such as injection pressure, injection frequency, and fluid temperature on the thermal effect of cavitation were analyzed. Computational fluid dynamics studies have revealed the bubble collapse process. The evolution of pressure and temperature inside and outside the bubble has been analyzed and validated by previous experimental observations. Different impact chambers have been tested for their cavitation performance, and the one with a cone shape shows superior performance over the other two. In the experimental observations, an increase in the injection pressure leads to an increase in the fluid temperature. An increase in injection frequency and chamber pressure facilitates the increase in ambient fluid temperature, while a further increase in fluid temperature hinders the cavitation heating process. A tubing configuration with a cavitation method is also proposed in this paper.

The high-pressure and low-temperature environment prevailing in the process of offshore oil and gas development is very prone to the formation of hydrate in the wellbore to block the tubing, which leads to production reduction and shutdown and causes a series of production accidents. Current mainstream hydrate prevention and treatment methods have the disadvantages of high cost, high toxicity and high pollution, and new and more effective hydrate prevention and treatment methods are urgently needed in the deep-water offshore well development. In this paper, the thermal effect of cavitation is introduced into the hydrate prevention and treatment process of deep-water offshore production wells, and the upper section of the completion tubing structure is designed to be applicable to the actual field. With the help of indoor experimental system, we have analyzed the influences of several working parameters such as the injection pressure, injection frequency, initial temperature of the fluid and the pressure inside the cavitator on the development of cavitation thermal effect. Preliminary conclusion drawn from both numerical simulation and experimental observations provides a new and possible way of natural gas hydrate prevention in near future.

In offshore gas well drilling and production, methane hydrate may block the tubing, resulting in the stoppage of gas production. Conventional methods such as injection of thermal hydrate inhibitors, thermal insulating or heating, gas dehydration and reducing pressure are time-consuming and expensive, and sometimes, they are not realistic in production conditions. New methods are needed to lower the cost of gas hydrate prevention and to overcome these limitations. The thermal effect of cavitation was applied to the prevention of gas hydrate in this study. The thermal impact of cavitation, supposed to heat the fluids and prevent the formation of gas hydrate, was evaluated. Numerical simulation was performed to study the thermal performance of cavitation. Furthermore, experimental studies of the influence of initial temperature, flow rate, fluid volume and fluid viscosity on the thermal effect of cavitation were performed, and the results were analysed.

Lost circulation usually happens when drill through fractured formation. A clear understanding of the circulation loss mechanism is key to successful drilling operations. More attention has been paid to fracture development and lost circulation materials (LCMs) composition. Much work still needs to be done on how the solid particles affect the overall fluid loss process in rough-walled fractures. The control equations for liquid-solid multiphase flow in a 2D rough-walled stationary fracture were established based on fundamental principles of fluid mechanics. Among these equations, the drilling fluid was treated as a Bingham type non-Newtonian fluid, and the influence of solid particles on fluid flow was analyzed in detail. The finite difference method was adopted to the numerical solution of the equations, and the impact of such working parameters as fracture dimensions, bottomhole pressure differential, physical properties of both fluid and particle on the fluid loss were analyzed. The following conclusions can be drawn from the paper: (1) the presence of solid particles can lower the leakoff rate and accumulative leakoff rate to various degrees; (2) the larger the fracture dimension, the lower the leakoff rate and accumulative leakoff rate; (3) the larger the pressure differential, the higher the leakoff rate and accumulative leakoff rate; (4) the leakoff rate and accumulative leakoff rate will decrease with the increase of particle diameter and its volume concentration; (5) particle sphericity and yield stress have little influence on the leakoff rate and accumulative leakoff rate. (6) The higher the plastic viscosity of drilling fluid, the lower the leakoff rate and accumulative leakoff rate. The limitations of this study, suggested improvement and future direction of current work are also highlighted.

Geothermal energy has gained more and more attention from all around the globe for its cleanness and efficiency. In the meantime, wells are drilling more and more deeper to develop oil and gas resources. Low rate of penetration is the common problem faced by geothermal wells and deep oil wells. To speed up the development of geothermal energy and petroleum resources in deep formation, a hydrothermal drilling method is proposed here in this paper and the drilling mechanism along with an in-lab experimental setup have been analyzed.

Hydrothermal Spallation Drilling (HSD) is a relatively new method suitable for drilling through hard and brittle rocks usually encountered in deep wells and more commonly in geothermal well drilling. Up to 70% of the cost of a geothermal energy project is spent on drilling since today almost all deep wells are drilled by conventional rotary drilling. Among all sustainable energy sources geothermal energy has an advantage of its energy production being independent of climatic conditions, however to allow installation of geothermal power plants geothermal wells have to be drilled at low costs. Conventional rotary drilling in hard formation is expensive because of bit wear which causes more tripping during drilling and hence increases the cost. Therefore, HSD comes in to save the cost of drilling by up to 15-20%. This document reviews the technology, its mechanism, status and future. With the global increment in the contribution of geothermal energy expected in the future, 5% of global energy by 2050, HSD is a game changing technology to increase the profitability and competitiveness of geothermal energy in relation with other sources of energy. However, just like any other technology HSD has shortfalls which are discussed in this document. These shortfalls have set a trend in the research world which has been mainly conducted in Switzerland and US. Overall assessment of the technology is promising and it will work to supplement conventional rotary drilling rather than replace it.

Well loss is one of the common complex downhole conditions during the drilling in fractured formations.On the basis of fluid dynamics theory, the control equation of fluid loss in 2D rough fractures has been established to basically understand the occurrence mechanism of fluid loss.During the deduction of such equation, drilling fluid is modeled as Bingham fluid and the fracture is described as 2D single fracture with rough surface, index deformation and dip angle.Finite element method is used to solve the fluid loss control equation;based on the created model, the loss laws of drilling fluid in a two-dimension rough fracture has been analyzed.Research results indicate that the smoother the fracture is, the greater the loss rate and the cumulative loss will be;the fracture dip has less impact on loss rate while affects the cumulative loss;the greater the fracture area is, the greater the loss rate and cumulative loss will be;the smaller the fracture length is, the greater the loss rate and cumulative loss will be;the greater the fracture width is, the greater the loss rate and cumulative loss will be;the fluid loss rate and cumulative loss have increased significantly as the downhole pressure difference increases;fluid dynamic shearing stress has less impact on loss rate, but has certain impacts on cumulative loss;the smaller the plastic viscosity is, the greater the loss rate and cumulative loss will be.

With the ever increasing global energy demand and diminishing petroleum reserves, current advances in drilling technology have resulted in numerous directional wells being drilled as operators strive to offset the ever-rising operating costs. In as much as deviated-well drilling allows drillers to exploit reservoir potential by penetrating the pay zone in a horizontal, rather than vertical, fashion, it also presents conditions under which the weighting agents can settle out of suspension. The present work is categorized into two parts. In the first part, governing equations were built inside a two-dimensional horizontal pipe geometry and the finite element method utilized to solve the equation-sets. In the second part, governing equations were built inside a three-dimensional horizontal annular geometry and the finite volume method utilized to solve the equation-sets. The results of the first part of the simulation are the solid concentration, mixture viscosity, and a prediction of the barite bed characteristics. For the second part, simulation results show that the highest occurrence of barite sag is at low annular velocities, nonrotating drill pipe, and eccentric drill pipe. The CFD approach in this study can be utilized as a research study tool in understanding and managing the barite sag problem.

The application of particle impact drilling ( PID) technology in hard and strong abrasive rock formations has a great potential for increasing drilling speed and efficiency. In this paper, the state of the art of the PID technology was de-scribed and its prospective development was analyzed based on an intensive literature survey in the area over the world and the author's active research work. The recent progress of the PID technology and its key aspects were summarized systemati-cally, including the particle injection and recovery systems and tools used for down-hole rock-breaking. Continuous and sta-ble injection of hard and abrasive particles into drilling fluid is essential to the PID application, and the homogenous distribu-tion of the particles in drilling fluid and their recovery on the surface are also important for the efficiency of the technology. Individualized design of the PID bit and optimum selection of the hydraulic paramenters are the key points of the current re-search. Improvement of the service life of the PID system and its stability is fundenmental for the application of the technolo-gy, which needs further research and breakthrough. On the mechanism study of the PID, it has been focused on the effects of dynamic loading and stress wave damage and softening of the particle jet on rocks and the combined jet-mechanical rock breaking mechanism, which are still the research fronts of the future study.

Sudden expansion nozzle is a typical application of fluid separation and reattachment. To get a better understanding of the flow mechanism, the fluid flow through a sudden expansion nozzle was investigated numerically with realizable k--ε turbulence model and appropriate boundary conditions. The reattachment point and the velocity distributions on different profiles were analyzed. Conclusions can be drawn from this paper that: (1) With the increase of Reynolds number, the reattachment point turns to be far and far from the origin or the corner of the nozzle. (2) There attachment point is around 8 times the nozzle height when the flow is fully turbulent. (3) As the flow develops towards the outlet, the reverse flow at the lower portion of the nozzle increases till it reaches its maximum value in the recirculation zone, and then decreases as the influence of recirculation zone is reduced.

The mixing chamber is an important part of the pre-mixed abrasive water jet generating sys-tem. Appropriate mixing chamber structure is benefit for the mixing of abrasive material and water to improve the u-tilization of hydro energy. Considering the interaction between the liquid and solid phase, the standard κ-ε turbu-lence model is applied to simulate the two-phase flow in the mixing chamber. Based on the nonuniformity of the mix-ing, statistical method was used to optimize the main structure parameters of the mixing chamber so that to attain optimized structure dimensions, test the abrasive material volume fraction and casing cutting. The study results show that the abrasive material volume fraction fluctuates around the calibration value within a narrow range after the optimization. The casing cutting efficiency is significantly improved and the cutting edge of casing is smoother, indicating an improved liquid-solid mixing performance of the optimized mixing chamber.

Previous studies show that cuttings are transported to wellhead by a rolling form for the hole section with high inclination,including horizontal section.A critical annular condition for the effective transportation of small-sized cuttings in highly deviated and horizontal well section is put forward,that is critical re-suspension velocity.On the basis of dynamics analysis on cuttings,a mechanical model for predicting the critical re-suspension velocity is established,which considers the effect of the rotation of drill pipe and the interparticle forces.The theoretical calculation results are compared with old experimental results,showing a good consistency.Using this model,the transportation process for small-sized cuttings is analyzed.The results show that the small-sized cuttings with diameters of less than 0.5 mm are more difficult to be re-suspended;the hole inclination has a limited effect on the critical re-suspension velocity in hole sections with high inclination;the rotation of the drill pipe is helpful for the re-suspension of small-sized cuttings;in some extent,the smaller the value of drilling fluid and consistency factor are,the more beneficial for the re-suspension of the small-sized cuttings is.

通过分析气体钻井井底岩石边界条件,建立了轴对称井底岩石物理模型。利用有限元方法求解,对1 000～3 000 m井深条件下的井底岩石应力场进行数值模拟计算,并对井眼轴线、井底面、井壁进行岩石力学特性分析。分析结果表明,井轴最大主应力在1.6～2.8倍井径距离后,应力逐渐低至水平地应力,破岩难度增加;井底面0.0～0.8倍井径区域存在低应力区,有利于岩石破碎;在井底面向上0.0～0.2 m井壁范围内出现拉应力增加趋势,易出现井壁失稳现象。

With the increment of the oil-field extract strength and the pipeline infusion load, the pipeline damage had become more serious and the effective use of cycle got shorter. Pipeline damage mainly appeared pipeline corrosion. The pipeline corrosion mainly occured in the place of pipe's repaired mouth and mending of blemishes. In this paper, through failure analysis of the pipe's Heat Shrinkable Wraparound Sleeve (HHWS) repaired mouth, we found the failure modes and failure causes of the repaired mouth of the existing pipeline and new pipeline, and grasped the failure mechanism. Then, improvement measures and suggestions were proposed to prevent failure, ensure safety, improve quality of the pipe's repaired mouth, slow or prevent pipeline corrosion and extend pipeline life.

Aiming at the situation that the bottom edge plates of oil tank often corrode in the process of long-term service, a kind of detection technology based on ultrasonic lamb wave had been developed. Relevant experimental study is carried out. The equipment for auto-testing tank is designed. Simulation analysis on the steel plate with the thickness of 14mm is conducted; the curve of excitation angle is calculated. The result is that for the lamb wave of A0 mode, optimum excitation angle is 70°. The experimental model with the ratio of one to one for refined oil tank bottom plate of 20000m 3 is designed and processed. By using designed UT350 flat guided wave testing system, the experiment is developed on the model plate, the best test results is obtained while the excitation signal frequency is 490 kHz. The result of experiment indicates that low frequency pulse signal of A0 mode lamb wave is able to detect the defects of largesized plates. The tank bottom automatically detection device that walks close to the storage tank wall is designed; the device is able to realize the continuous, high efficiency, and stability online detection process for the defect of oil tank bottom plate . The research results and designed device achieve the defect detection for the bottom plate of oil tank. The technique provides security for the safe operation of the storage tank.

The flow over a stationary spherical abrasive particle was studied numerically to analyze the effects of turbulent parameters（turbulence intensity and turbulent viscosity ratio） on the drag force of an abrasive particle.Several turbulence models were verified by using the models to analyze the submerged impinging jet.The Reynolds stress model was chosen to simulate the turbulent flow over the abrasive particle.The turbulence intensity varied from 5% to 70% and the turbulent viscosity ratio varied from 1 to 1200.Conclusions can be drawn from the simulation that with the increase of turbulence intensity,the drag force on the abrasive particle increases and with the increase of turbulent viscosity ratio the drag force on the abrasive particle also increases.

This paper gives an overview of erosion mechanisms in elbows in oil and gas production systems. The nature of the erosion process itself makes it very difficult to develop some definitive methods or models to prevent or predict the erosion in elbows in all conditions. This paper provides a review of the subject which will help petroleum engineers to handle the erosion problems in oil and gas industry. This review is given of different erosion mechanisms connected with sand erosion and the factors that influence them, and then the review goes on to look at particulate erosion in elbows in more details. Conclusions are then drawn based on the above analyses.

To evaluate the predictive capabilities of K-E turbulence models, three turbulence models (the standard K-E model, the RNG K-E model and the Realizable K-E model) in conjunction with a fully-developed boundary condition and a standard wall function were applied to the prediction of a fully-developed two-dimensional jet impinging within a semi-confined space. The convection term and the dissipation term in the control equations were discretized by Second Order Upwind scheme and Central Differencing scheme. The numerical results, including the time-averaged velocities and the turbulence intensities, were compared with the experimental data reported by Yoshida. It was found that the numerical results were in qualitative agreement with the experimental data. The differences between the numerical and experimental results can be attributed to the fundamental assumptions of the turbulence models, experimental error and the treatment of the low Reynolds number zone near the impingement wall.

Abrasive water jet cutting technology (AWJCT) has found its wide applications in the machining of ceramics, quartz and compound materials. During the machining process, AWJCT shows superior performance on the cutting efficiency, the flexibility and no heat-affected zone. Yet one disadvantage of AWCT is that the control of the whole cutting process is not as easy as those in mechanize cutting or in plasma cutting. To solve the problem, analyses are performed in this paper to find out the proper method to manipulate AWJCT. Conclusions can be drawn from these analyses that the power spectrum density can be used as an indication to manipulate the pump pressure or the traverse speed so as to meet the requirement of cutting depth. The expert system based on these linear or nonlinear relationships can meet the need of automatic control of AWJCT.

A Realizable k-ε turbulence model in conjunction with a standard wall function has been applied to the prediction of a fully-developed two-dimensional jet impinging within a semi-confined space. A single geometry with a Reynolds number of 10,000 and a nozzle –to-plate spacing of eight diameters has been considered at different inlet boundary conditions. The numerical results, including the time-averaged velocities and the turbulent intensity, have been compared with the experimental data reported by Yoshida (ref 5). It is found that the trends in the axial velocity, the radial velocity and the turbulent intensity are fairly predicted. The fully-developed boundary condition is generally better than the constant velocity boundary condition. The differences between the numerical and experimental results can be attributed to the turbulence model and the treatment of the low Reynolds number zone near the wall.