致密油藏体积压裂缝网形成及控制方法研究

发布时间：2018-06-19 17:56

本文选题：致密油 + 体积压裂　；参考：《东北石油大学》2017年博士论文

【摘要】：体积压裂技术是致密油开发的关键技术之一,大庆油田致密油开发尚处于起步阶段,对致密储层的力学性质参数、岩石可压性评价、人工裂缝扩展机理等方面研究较少,国内外目前研究成果适应性差。因此,开展致密油藏体积压裂缝网形成机理和控制方法研究,对实现致密储层的成功体积改造以及致密砂岩油藏的商业化开发具有重要意义。本文以大庆长垣南部地区扶余油层致密储层为研究对象,采用室内试验、理论分析和数值模拟相结合的手段,对天然裂缝发育程度低的致密砂岩油藏可压性、压裂缝网形成机理及工艺控制方法进行了研究。由于致密材料在力学上表现为高强度和高硬度的特征,因此采用高温高压岩石动态三轴仪对扶余油层致密油试验区岩心样品开展了储层力学参数测定和评价,和常规储层不同,埋深对致密砂岩力学性质有显著的影响,致密岩样抗压强度和弹性模量随围压的增大而增大,不同取样方向的致密砂岩试样应力-应变曲线形态比较相似。考虑致密储层体积压裂过程中岩石变形破坏形式复杂,因此基于岩石断裂过程中的能量演化,建立了能够反映岩石整体破坏过程的致密岩石脆性评价指数。利用该脆性指数结合测井数据以及室内力学试验数据和脆性矿物含量分析,能够对致密储层可压性进行综合的评定,研究表明本文试验所用砂岩样品在地层条件下具有较高的脆性,可压性较好,为致密储层体积压裂缝网形成机理研究奠定基础。和页岩、煤岩相比,扶余油层致密岩石中没有层理、割理等结构弱面,且天然裂缝发育程度低,因此建立了天然裂缝欠发育条件下致密储层应力释放缝形成力学模型,研究了应力诱导裂缝的形成条件、延伸方向以及延伸条件,揭示了致密储层复杂裂缝网络形成机理。随后建立了人工裂缝沿初始装状态为闭合的天然裂缝剪切转向的判别模型,研究得到了水平应力差、逼近距离、逼近角、缝内净压力以及裂缝特征对剪切失稳区的影响以及影响范围。在此基础上,建立了考虑多孔介质流固耦合效应、压裂液法向滤失和切向流动的压裂诱导地应力数值模型,研究认为致密储层体积压裂缝网形成的主控因素主要有缝内净压力、人工裂缝间距、裂缝长度、岩石性质等因素,缝内净压力越大、裂缝间距越小、裂缝长度越长,应力差越小,越有利于网状裂缝的形成。基于以上研究结果,提出了致密储层体积压裂缝网形成的控制方法,结合实际工程因素,从压裂液体系、注入排量、人工裂缝间距等方面研究了天然裂缝欠发育的致密砂岩储层体积压裂缝网控制工艺方法,现场应用效果较好,证实了本文提出的体积压裂方式可有效增加缝网规模,本文研究方法和成果同时也可在类似致密储层及其他非常规储层借鉴应用。
[Abstract]:Volume fracturing is one of the key technologies in the development of dense oil. The development of dense oil in Daqing Oilfield is still in its infancy. There are few researches on the parameters of mechanical properties of tight reservoir, the evaluation of rock compressibility and the mechanism of artificial fracture propagation, etc. The adaptability of current research results at home and abroad is poor. Therefore, it is of great significance to study the formation mechanism and control method of volume fracturing network in dense reservoir, which is of great significance to realize the successful volume reconstruction of tight reservoir and the commercial development of tight sandstone reservoir. In this paper, the dense reservoir of Fuyu reservoir in the southern area of Daqing Placanticline is taken as the research object. The compressibility of tight sandstone reservoir with low degree of natural fracture development is studied by means of laboratory test, theoretical analysis and numerical simulation. The forming mechanism and process control method of pressure fracture net are studied. Because the dense materials are characterized by high strength and high hardness in mechanics, the determination and evaluation of reservoir mechanical parameters are carried out by using the dynamic triaxial instrument of high temperature and high pressure rock in the dense oil test area of Fuyu reservoir, which is different from the conventional reservoir. The compressive strength and elastic modulus of dense rock samples increase with the increase of confining pressure, and the stress-strain curves of compact sandstone samples with different sampling directions are similar. Considering the complexity of rock deformation and failure in the process of bulk fracturing of tight reservoir, an evaluation index of rock brittleness is established based on the energy evolution during rock fracture. By using the brittle index, well logging data, laboratory mechanical test data and brittle mineral content analysis, the compressibility of tight reservoir can be comprehensively evaluated. The results show that the sandstone samples used in this paper have high brittleness and good compressibility under stratigraphic conditions, which lays a foundation for the study of formation mechanism of tight reservoir pressure fracture network. Compared with shale and coal rock, there is no stratification, weak surface of cleat and so on in dense rock of Fuyu reservoir, and the degree of development of natural fracture is low. Therefore, a mechanical model of tight reservoir stress release fracture formation under the condition of underdevelopment of natural fracture is established. The formation conditions, extension direction and extension conditions of stress-induced fractures are studied, and the formation mechanism of complex fracture networks in dense reservoirs is revealed. Then, a discriminant model of natural crack shearing steering along initial loading state is established, and the horizontal stress difference, approaching distance and approaching angle are obtained. The influence of net pressure and fracture characteristics on shear instability zone and its influence range. On this basis, a fracturing induced stress numerical model considering the fluid-solid coupling effect of porous media, the normal filtration and tangential flow of fracturing fluid is established. It is considered that the main controlling factors for the formation of volume fracturing network in dense reservoirs are net pressure within fractures. The larger the net pressure, the smaller the crack spacing, the longer the crack length and the smaller the stress difference, the more favorable the formation of network fractures. Based on the above research results, the control method of forming tight reservoir volume fracturing network is put forward. According to the actual engineering factors, the injection and displacement of fracturing fluid system are carried out. The control technology of volume pressure fracture network in tight sandstone reservoir with underdeveloped natural fractures is studied in terms of artificial fracture spacing. The field application results show that the volume fracturing method proposed in this paper can effectively increase the size of fracture network. The research methods and results in this paper can also be used for reference in similar tight reservoirs and other unconventional reservoirs.
【学位授予单位】：东北石油大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TE357

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