油页岩水平井水力压裂裂缝起裂与延伸机理研究

发布时间：2018-07-05 14:53

本文选题：油页岩 + 水平井　；参考：《吉林大学》2017年博士论文

【摘要】：能源是人类社会发展的动力和基石,从煤炭到石油,再到天然气,世界能源消费结构不断调整。进入二十一世纪以来,我国经济继续保持快速稳定发展,逐渐成为带动世界经济发展的心脏,而我国却是一个“富煤贫油少气”的国家,这将会制约我国经济的持续发展。因此,确保油气能源的持续供应是我国未来经济可持续发展的重要基础。油页岩作为一种重要的石油替代能源,在全世界范围内分布广泛,且资源储量巨大,仅我国0~1000m埋藏的油页岩折算成油页岩油约476.44亿吨,远高于目前国内常规石油资源量,油页岩油资源量在世界排名第二。因此,加快我国油页岩勘探开发力度,实现油页岩油的工业化生产,弥补我国常规油气产量不足,逐步形成常规与非常规油气共同发展的格局,对优化我国能源消费结构,保障我国经济持续稳定发展至关重要。然而,由于油页岩内有机质不能以常规油气资源的开发方式直接开采,必须通过一定的加热手段将油页岩内干酪根裂解来产出油气。所以国内外科研机构正在研究多种油页岩的开发手段,其中油页岩原位转化技术凭借其对环境友好的特点,将会成为未来油页岩开发的重要手段。本文以油页岩原位转化技术为研究背景,针对油页岩原位转化技术需要通过水力压裂来提高油页岩地层传热效率、渗透性及出油率等客观情况,对油页岩地层中水平井水力压裂裂缝起裂与延伸机理进行研究。文章采用了理论分析手段对油页岩水平井水力压裂裂缝起裂和延伸进行分析,分析认为:油页岩地层中层理发育而且存在天然裂缝,裂缝的起裂会以从本体起裂、沿天然裂缝张性起裂、沿天然裂缝剪切起裂三种起裂模式,并分别给出了判断依据;而针对裂缝在延伸过程中可能会遇到天然裂缝的情况给出裂缝穿过裂缝的判断依据。为了掌握油页岩力学特性对油页岩裂缝延伸的影响,本文对油页岩垂直层理和平行层理方向的力学特征进行了多组物理力学试验,得到两个方向的单轴抗压强度、抗拉强度、弹性模量以及泊松比等力学参数,并采用X射线衍射对油页岩不同层理面上的矿物成分进行了检测分析,得到不同层理面的XRD谱图,同时采用声发射手段对油页岩试样进行断铅试验,得到不同层理角度的油页岩纵横波波速。研究结果表明:油页岩垂直层理和平行层理方向的力学特征存在很大差异,具有明显的各向异性,而且层理之间存在矿物成分的差异,结合不同层理夹角方向的纵横波波速变化规律,分析认为水力裂缝在油页岩垂直层理方向延伸时更容易形成形态复杂的裂缝网络,但是沿着水平方向延伸时可能仅形成两翼对称裂缝,裂缝形态具有方向性。为了掌握裂缝参数对油页岩原位转化的影响,以吉林大学提出并进行野外先导试验的油页岩原位注氮气开采工艺为背景进行原位加热过程模拟研究,对不同裂缝宽度、裂缝间距条件下油页岩原位注氮气加热油页岩层的地层平均温度、加热时间以及出油量进行了模拟分析,模拟结果表明:不同缝宽条件下,油页岩地层的加热效果相差不大,而缩小裂缝间距,油页岩地层加热效果有非常明显的提高,因此在进行油页岩层水力压裂时,在地层形成多条窄裂缝更有利于加快油页岩地层加热速率,提高投产比,减小开采成本。同时建立二维油页岩横向各向同性模型,采用扩展有限元方法(xfem),对不同应力组合、泵注排量以及预制裂缝与层理夹角等条件下裂缝扩展影响进行数值模拟研究。研究表明:水力裂缝在油页岩中扩展时,应力条件和层理方向是影响裂缝扩展方向的主要因素,如果初始水力裂缝不在最优扩展路径,会产生裂缝偏转,裂缝偏转会减小水力裂缝的有效扩展长度,增大裂缝起裂和延伸压力。最后采用自主研制的真三轴水力压裂物理模拟试验系统进行油页岩水平井水力压裂模拟试验,以及水泥砂浆水平井水力压裂对照试验,对水力裂缝的起裂和延伸受原地应力系统、压裂液排量和黏度、水平井筒方位和倾角等因素的影响规律进行试验分析。研究表明:油页岩水平井起裂压力受井筒倾角、方位、排量以影响较大;裂缝形态主要由横断裂缝,层理裂缝以及纵向裂缝三种裂缝组成;油页岩地层本身各向异性以及天然裂缝系统或者弱结构面是形成网络裂缝的关键因素,裂缝延伸遇到天然裂缝或弱结构面会发生转向或穿过,不断沟通地层本身裂缝,扩大裂缝范围。另外水平地应力差异系数越小,井筒倾角越大,越容易形成复杂网络状裂缝。如果油页岩上覆地层或者下伏地层弹性模量、抗拉强度等力学特征大于油页岩层,且存在弱胶结面,当裂缝在延伸至二者胶结面时,裂缝不能穿过胶结面进入上下层,而会沿着胶结面延伸,否则会延伸至其他地层。本文对油页岩水平井水力压裂过程中裂缝起裂和延伸机理进行了系统的分析,并指出油页岩地层中形成复杂网络状裂缝的关键是油页岩地层本身各向异性及天然裂缝系统或者弱结构面,并提出影响裂缝复杂程度的因素,为未来油页岩水力压裂设计提供借鉴,从而提高油页岩原位转化工艺开采效率。
[Abstract]:Energy is the motive force and cornerstone of the development of human society. From coal to oil to natural gas, the energy consumption structure of the world is constantly adjusted. Since twenty-first Century, China's economy continues to maintain rapid and stable development and gradually become the heart of the development of the world economy, but China is a "rich coal rich and less gas" country, this will be Therefore, the sustainable development of China's economy is restricted. Therefore, to ensure the continuous supply of oil and gas energy is an important basis for the sustainable development of our economy in the future. As an important alternative energy for petroleum, oil shale is widely distributed throughout the world and has a huge reserve of resources. Only about 47 billion 644 million of the oil shale oil buried in 0~1000m in China is converted into oil shale oil about 47 billion 644 million. Tons, far higher than the current domestic conventional oil resources, oil shale oil resources in the world ranked second in the world. Therefore, to speed up the exploration and development of oil shale in China, realize the industrial production of oil shale oil, make up for the shortage of conventional oil and gas production in our country, gradually form the common development pattern of conventional and unconventional oil and gas, and optimize the energy consumption of our country. However, because the organic matter in the oil shale can not be directly exploited by the development of conventional oil and gas resources, the kerogen in the oil shale must be cracked to produce oil and gas through a certain heating means. Therefore, the research institutions at home and abroad are studying the development means of various oil shale. In situ conversion technology of oil shale will be an important means of developing oil shale in the future. In this paper, the in-situ conversion technology of oil shale is used as the research background. In order to improve the heat transfer efficiency, permeability and oil production rate of oil shale formation by hydraulic fracturing, the oil shale in-situ transformation technology is required to improve the oil shale formation. The crack initiation and extension mechanism of hydraulic fracturing in horizontal wells in shale formation is studied. The theoretical analysis method is used to analyze the fracture and extension of hydraulic fracturing fractures in oil shale horizontal wells. In order to grasp the influence of the mechanical properties of oil shale on the fracture extension of oil shale, the vertical bedding of oil shale is peaceful. The mechanics characteristics of the row bedding direction are carried out in many groups of physical mechanics tests, and the mechanical parameters such as uniaxial compression strength, tensile strength, modulus of elasticity and Poisson's ratio are obtained in two directions, and the mineral composition on the different bedding surfaces of oil shale is detected and analyzed by X ray diffraction, and the XRD spectrum of different bedding surfaces is obtained, and the sound is used at the same time. The results show that there is a great difference in the mechanical characteristics of the vertical and parallel bedding directions of the oil shale, with the obvious anisotropy, and the difference in the mineral composition between the layers and the angle square of different bedding. It is believed that the fracture network is more easily formed when the hydraulic fracture is extended in the vertical direction of the oil shale, but it may only form two symmetrical fractures in the horizontal direction, and the shape of the fracture is directional. In the field of field pilot test, the in-situ heating process of the oil shale in situ was simulated. The average temperature, the heating time and the oil output of the oil shale in the oil shale were simulated and analyzed. Under the conditions of different seam width, the heating effect of oil shale formation is not quite different, and the gap between the cracks is narrowed, the heating effect of oil shale strata is greatly improved. Therefore, in the hydraulic fracturing of oil shale strata, forming a number of narrow cracks in the formation is more conducive to speed up the heating rate of oil shale formation, increase the production ratio and reduce the cost of mining. At the same time, the transverse isotropic model of two dimensional oil shale is established, and the extended finite element method (XFEM) is used to simulate the effects of different stress combinations, pump displacement, prefabricated cracks and bedding angle. The study shows that the stress and bedding direction of hydraulic cracks are affected by the expansion of hydraulic cracks in the oil shale. The main factor of the direction of slit expansion is that if the initial hydraulic crack is not the optimal expansion path, the crack deflection will occur, the transfer of the cracks will reduce the effective expansion length of the hydraulic fracture and increase the crack initiation and extension pressure. Finally, the hydraulic fracturing of the oil shale horizontal well is carried out by the self developed real three axis hydraulic fracturing physical simulation test system. The simulation test, as well as the hydraulic fracturing control test of the cement mortar horizontal well, test and analyze the effect of the fracture and extension of the hydraulic fracture on the ground stress system, the displacement and viscosity of the fracturing fluid, the horizontal wellbore and the inclination angle. The study shows that the pressure of the horizontal well is affected by the angle of the wellbore, the azimuth and the displacement. The fracture morphology is mainly composed of three kinds of cracks: transverse cracks, bedding cracks and longitudinal cracks; the anisotropy of the oil shale formation itself, the natural fracture system or the weak structural surface are the key factors to form the network cracks, and the fracture extension meets the natural or weak structural surfaces to turn or pass through, and constantly communicate the formation itself cracks. In addition, the smaller the difference coefficient of the horizontal stress, the smaller the difference coefficient of the horizontal stress, the greater the angle of the wellbore, the more easy to form a complex network fracture. If the oil shale overlying strata or the elastic modulus of the underlying strata, the tensile strength is larger than the oil shale, and there is a weak cementation surface. When the crack extends to the two cementing surface, the cracks can not be worn. The cementation surface goes into the upper and lower layers and extends along the cementation surface, otherwise it will extend to other strata. This paper systematically analyses the crack initiation and extension mechanism in the hydraulic fracturing process of oil shale horizontal wells, and points out that the key of the formation of complex network cracks in the oil shale formation is the anisotropy and natural crack of the oil shale formation itself. The fracture system or the weak structural surface, and the factors that affect the complexity of the fracture, can be used for reference for the hydraulic fracturing design of oil shale in the future, thus improving the efficiency of the oil shale in situ conversion process.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TE357.1

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