论文中文题名: | 花岗岩水力压裂特征与裂隙渗流换热规律研究 |
姓名: | |
学号: | 20204228098 |
保密级别: | 保密(1年后开放) |
论文语种: | chi |
学科代码: | 085900 |
学科名称: | 工学 - 土木工程 - 建筑与土木工程 |
学生类型: | 硕士 |
学位级别: | 工程硕士 |
学位年度: | 2023 |
培养单位: | 西安科技大学 |
院系: | |
专业: | |
研究方向: | 岩土力学与工程应用 |
第一导师姓名: | |
第一导师单位: | |
论文提交日期: | 2023-06-12 |
论文答辩日期: | 2023-06-03 |
论文外文题名: | Study on characteristics of granite hydraulic fracturing and law of seepage heat transfer in fracture |
论文中文关键词: | |
论文外文关键词: | Hot Dry Rock ; Hydraulic fracturing ; Crack extension ; Seepage ; Heat exchange ; Numerical simulation |
论文中文摘要: |
地热能作为一种分布广泛的可再生资源,已成为人类可利用的第三大可再生能源。干热岩型地热能因其储量巨大和清洁、高效、可再生的特点具有十分重要的研究意义。目前干热岩开采通常需要通过水力压裂实现,以提高干热岩储层渗透性。作为分布广泛的一种干热岩储层,花岗岩的水力压裂特征和渗流换热规律仍未系统揭示,需要进一步研究。本文以花岗岩为研究对象,研究了不同围压、温度下水力压裂特征;分析了压裂过程中声发射特征演化规律;阐明了裂隙扩展规律;厘清了水力压裂影响因素;揭示了水力压裂破裂机制和裂隙扩展准则;通过数值模拟手段研究了压裂裂隙渗透特性和裂隙岩体渗流换热规律。主要得到以下结论: 1.水力压裂曲线可以分为4个明显的阶段:(a)管孔充水;(b)钻孔增压;(c)压裂;(d)裂隙延伸。在压裂阶段可以同时观察到明显的孔压下降和围压上升。声发射信号的第一次大规模增加大致发生在孔压达到破裂压力时。声发射信号发生剧增意味着主裂隙的萌生,信号多次波动意味着裂隙的扩展。声发射手段监测裂隙的萌生与扩展相比孔压更灵敏,不仅可以监测宏观的破裂现象,也可以监测细观的微破裂。 2.压裂后的裂隙均沿着试样的钻孔方向竖向扩展,随着围压的增加,裂隙长度越来越大,裂隙路径越来越复杂。压裂裂隙并非从试样的顶部起裂,起裂于距离试样顶部的某个位置。裂隙较为粗糙且相当曲折,主裂隙周围有一定数量的次级裂隙,部分地方由于颗粒破碎,导致局部裂隙开度较大。裂隙既存在沿晶断裂,也存在穿晶断裂。 3.水力压裂特征受围压影响明显,结果表明:温度一定时,围压越大,破裂压力越大,二者的关系近似呈线性。围压越大,破裂时间越长。在热冲击现象不显著的情况下,围压一定时,温度越高,破裂压力越大。花岗岩水力压裂主导破裂机制为张拉破裂,但裂隙仍存在剪切破裂特征。破裂压力是围压、温度和岩石材料性质的函数。水力裂隙扩展集中的一部分区域称为优势裂隙扩展区。当裂隙尖端的应力强度因子KI大于等于岩石的临界应力强度因子KIC时,裂隙开始扩展。 4.不同入口压力工况下,压力数值都沿着轴向方向均匀减小。在流体流动通道的同一方向上,各工况下水的速度场分布近似相同,随着入口压力的不断增大,水渗流的整体速度明显增大。粗糙裂隙中的流态较为复杂,裂隙中的流速并非均匀,随着几何形貌的变化而变化。越靠近裂隙面突起处,渗流速度越大,越靠近裂隙面凹陷处,渗流速度越小。 5.裂隙水温沿长度方向逐渐增大,水流出口处,裂隙水温与岩体温度接近相等。越接近水流出口处,温度等值线越稀疏。入口温度的增大可以提高裂隙水温,但不会影响岩体的温度梯度,对出口温度的影响也不大。入口速度越大,换热面积越大,裂隙周边的岩体温度梯度越大,岩石和裂隙水换热充分性也越小,岩体整体温度越低。水流流速减小,可使水岩换热更为充分。入口速度越大,对流换热系数越大。增大入口速度可以大幅提高换热效率。 本研究结果为花岗岩水力压裂和渗流换热规律的研究提供了理论依据,为干热岩地热能的开采提供了一定的参考。 |
论文外文摘要: |
As a widely distributed renewable resource, geothermal energy has become the third renewable energy available to human beings. Hot dry rock geothermal energy is of great significance because of its huge reserves, clean, efficient and renewable characteristics. Currently, hot dry rock production is usually achieved through hydraulic fracturing to improve the permeability of hot dry rock reservoir. As a widely distributed hot dry rock reservoir, the hydraulic fracturing characteristics of granite and the law of seepage heat transfer have not been systematically revealed and need further study. In this paper, granite is taken as the research object to study the hydraulic fracturing characteristics under different confining pressures and temperatures. The evolution law of AE characteristics in fracturing process is analyzed. The law of crack propagation is expounded. The influencing factors of hydraulic fracturing are clarified. The fracture mechanism and fracture propagation criterion of hydraulic fracturing are revealed. The permeability characteristics of fractured fracture and the law of seepage heat transfer in fractured rock mass are studied by numerical simulation. The main conclusions are as follows: (1)The hydraulic fracturing curve can be divided into four distinct stages: (a) water filling of pipe holes; (b) pressurization of boreholes; (c) fracturing; (d) fracture extension. A significant decrease in pore pressure and an increase in confining pressure can be observed at the same time during the fracturing stage. The first large scale increase of AE signal occurs roughly when pore pressure reaches breakdown pressure. The increase of AE signal means the initiation of the main crack, and the signal fluctuation means the expansion of the crack. AE method is more sensitive to monitoring the initiation and propagation of cracks than the pore pressure, which can not only monitor the macroscopic fracture phenomenon, but also monitor the microscopic micro-fracture. (2)After fracturing, the fracture extends vertically along the drilling direction of the sample. With the increase of confining pressure, the fracture length becomes larger and the fracture path becomes more and more complex. The fracture fracture does not start at the top of the sample, but at a certain position away from the top of the sample. The cracks are rough and tortuous. There are a certain number of secondary cracks around the main crack, and the local crack is larger due to particle breakage in some places. There exists both intergranular fracture and transgranular fracture. (3)The characteristics of hydraulic fracturing is obviously affected by confining pressure. The results show that the higher the confining pressure is, the greater the fracture stress is, and the relationship between them is approximately linear. The larger the confining pressure, the longer the breakdown time. When the thermal shock phenomenon is not significant and the confining pressure is constant, the higher the temperature, the greater the breakdown pressure. The dominant fracture mechanism of granite hydraulic fracturing is tensile fracture, but shear fracture still exists. Initiation pressure is a function of confining pressure, temperature and rock material properties. A region of the hydraulic fracture propagation concentration is called the dominant fracture propagation zone.When the stress intensity factor (KI) at the crack tip is greater than or equal to the critical stress intensity factor (KIC), the crack begins to expand. (4)Under different inlet pressure conditions, the pressure value decreases uniformly along the axial direction. In the same direction of the fluid flow channel, the velocity field distribution of the water under different conditions is approximately the same. With the increasing of the inlet pressure, the overall velocity of water seepage increases obviously. The flow pattern in the rough crack is more complicated, and the velocity in the crack is not uniform, which changes with the change of the geometric morphology. The closer to the fracture surface protrusion, the larger the seepage velocity is, and the closer to the fracture surface depression, the smaller the seepage velocity is. (5)The water temperature of the fissure increases gradually along the length direction, and the water temperature of the fissure is close to that of the rock mass at the flow outlet. The closer the flow outlet is, the thinner the temperature contour is. The increase of inlet temperature can improve the water temperature of crack, but it does not affect the temperature gradient of rock mass, and has little effect on outlet temperature. The larger the inlet velocity, the larger the heat transfer area, the larger the temperature gradient of rock mass around the fracture, the smaller the heat transfer adequacy of rock and fissure water, and the lower the overall temperature of rock mass. When the flow velocity decreases, the heat transfer between water and rock becomes more adequate. The larger the inlet velocity, the larger the convective heat transfer coefficient. Increasing the inlet speed can greatly improve the heat transfer efficiency. The research results of this paper provide a theoretical basis for the study of granite hydraulic fracturing and seepage heat transfer law, and provide a certain reference for the exploitation of geothermal energy in hot dry rock. |
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中图分类号: | TU458 |
开放日期: | 2024-06-13 |