Study On Solid Particles Erosive Wear Mechanism Of Oil And Gas Well Tubing String

Oil and gas well tubing string is a necessary tool in petroleum and natural gas exploitation industry. In recent years, with the exploration and exploitation of deep oil and gas fields, the increasing proportion of deep well, ultra-deep well, high-inclination well, directional well, extended reach well and horizontal well has already become a kind of inevitable trend. The work environment of tubing string in oil and gas well has deteriorated sharply, especially the high temperature, high pressure and high production oil-gas wells. Inevitably, oil and gas well tubing string suffered from all kinds of damage, which may result great waste of the human, material and financial resources. Research on various factors of affecting its reliability and service life have found that the particles erosion damage of oil and gas well tubing string is one of the main reasons for its failure.Erosion will directly lead to a serious loss of wall thickness of the equipments and tubing string, weakening their yield strength, reducing their service life and causing the hidden dangers. For example, leakage risk of poisonous and harmful gas such as hydrogen sulfide. When the erosion degree of the tubing string is mild, it will cause the peeling off of pipeline’s surface strengthened layer, and reduce the collapsing strength and internal pressure strength of the tubing string, which constitutes a serious threat to the safe of normal oil production; when the erosion is serious, the limited bearing capacity of tubes is reduced, which will lead to the tube’s deformation, collapsing, rupture or leaking, and cause the security issues such as control of oil and gas well. If repair and replacement working is not in time, it will eventually result in the rupture of oil-gas pipeline, that causing blockage, leakage and other down-hole accidents and even lead to terrible accident such as abandonment of whole well.To better understand the failure mechanism of solid particle erosion in pipe components, it is necessary to analyze the fluid flow characteristics of the tubes, track the trajectory of the particles, and study the erosion rate of oil and gas well tubing string. CFD software was applied to simulate pipe flow to find position where erosion weakness quickly and accurately, which predicting solid particle erosion damage state of the ground equipment and pipe wall. It will provide the theory foundation for the safety assessment of the equipment in oil and gas production, which contribute to take appropriate measures to mitigate erosion for prolong the service life of the equipment. It is important to reduce its cost and enhance the economic efficiency.This thesis summarizes prevailing particle erosion theories, and a comparison has been made between the six methods with respect to their advantages and disadvantages as well as applicability. Combined with the actual working environment of the particle erosion in the oil and gas well tubing string, the article establishes wear mechanism of particle erosion. Three factors affecting the erosion damage are concluded including environmental factors, abrasive performance and target material properties. This thesis also analyzes the force model of single solid particle in liquid flow in detail. And according to the movement differential equations of particles, analyzes their following features, and establishes a mathematical model between impact depth and particle velocity, impact angle and the flow stress of the target material. From the perspective of theoretical analysis, a preliminary explanation was made for the sharp particle has better erosion damage than the round one.This thesis has studied three kinds of erosion experiment devices in detail including circulating pipe flow erosive wear equipment, rotary erosive wear equipment and jetting erosive wear equipment, comparative analysis show the feature of each kind of equipment. In combination with the operating conditions of tubing string in the oil industry, screening the best suitable test device for this subject, and developing a strategy is necessary to research the particle erosion damage mechanism under the high stress environment.In this paper, the discrete phase model in commercial computational fluid software Fluent is adopted to simulate the tube’s wall erosion under hydraulic fracturing conditions, compared with real experiment, the investment is less, design and research period is shorter. The numerical simulation takes into consideration of various factors, and get complete data under different situation, which has significant advantages.UDF can used to define the particle properties and initial velocity, as well as improve the algorithm, which has a good operability. Based on Finnie cutting wear equation, make program to calculate erosion rate, quantizing the erosion rate associated with particle velocity and impact angle. It can be dynamically linked to the DPM solver, calculating the particle erosion rate of the tubing connector, the tubing-casing annulus and orthogonal double bend under the condition of hydraulic fracturing for predicting erosion risk. By means of calculated liquid velocity distribution and particle trajectories, erosion tendency has been analyzed preliminarily, afterwards draw relational curve between erosion rate and main erosion parameters including fracturing displacement, fluid viscosity, particle size, density, shape factor and so on. Compare curve results with qualitative analysis outcome to verify erosive wear mode’s reliability. The research results contribute to put forward the rationalization suggestion for fracturing construction technology, and provide important reference and guiding significance in conducting field operation.The performance of this dissertation obtains the main conclusions as followed:1. Combining with the operating condition characteristics of the oil and gas well tubing string, put forward that erosion wear is a substantial cause to promote tubing string failure;2. Analyze the action forces of single solid particle in depth, discuss the following features, and based on the theorem of momentum, establish a mathematical model between impact depth and particle velocity, impact angle, shape factor and the flow stress of the target material.3. Screen test equipment, design an experimental scheme to research the particle erosion damage mechanism under the high stress environment.4. According to UDF, define the function of erosion rate, quantitatively analyze the effects of erosion factors and point out that the erosion damage is mild in the straight segment, and the most serious erosion areas appear on the inside surface of tubing at the downstream end of tubing connector, the front slope of outer surface of the tubing coupling in tubing-casing annular space and tubing extrados is subjected to more severe erosion damage than tubing intrados in the bend region. In addition, erosion rate rises with the increase of impact velocity, as well as the size of particles, but the maximum erosion rate is almost constant with the particles in size of0.65mm. Fluid viscosity probably has a significant effect on particle suspension. It results in considerably less erosion in viscous fluids, when the liquid viscosity reaches a certain level the erosion rate tends to be stable. Particle shape is one of the major factors of influence on erosion. The more trenchant edges and corners of the particles, the more serious of erosion wear. Compared with the shape factor, the influence of particle density to erosion rate is extremely weak.