页岩储层水平井水力裂缝起裂与扩展特征的数值模拟分析

发布时间：2018-12-18 18:58

【摘要】：受页岩储层低渗透物性的影响,页岩气(油)藏需要经过水力压裂改造后才能开采。由于水平井在增加与储层接触面积、降低费用、拥有长期的稳产能力等方面具有明显的优势,它在页岩气开发中得到了广泛的应用,尤其是与滑溜水多级压裂相配合时,增产效果更为显著。绝大多数压裂作业是在套管射孔完井之后进行的,而水力裂缝的起裂与页岩岩石力学特性和页岩储层力学性质的非均匀性息息相关,因而射孔完井后实际的裂缝起裂和延伸是复杂多样的。此外,页岩储层常发育有大量天然裂缝和层理,对页岩储层的水力压裂可形成大规模网状裂缝,这就是通常的体积压裂的效果。本文在中国石油科技创新基金资助项目(2013D-5006-0211)、国家自然科学基金资助项目(51479024)、国家重点基础研究计划973项目(2014CB047103)的资助下,基于对前人阐述的岩体水力压裂机理的认识,从压裂过程中水力耦合作用的渗流-应力-损伤模型出发,并使其在有限元软件RFPA渗流版中实现,对有限的岩心物理实验结果进行了模拟和分析评价,得到后续有关章节相关的实验参数,进而开展对页岩储层水平井水力裂缝的起裂和扩展特征的数值模拟研究。首先,对水平井定向射孔水力裂缝的起裂特征进行了数值模拟研究,并就地应力差和射孔方位角两因素对其影响建立数值模型展开了详细分析,得到的结果显示有水力裂缝可能不在射孔端起裂的情况,在此基础上,进一步探讨了压裂双裂缝形成的可能性和条件。此外,模拟了裂缝延伸至产层与隔层界面处的穿层现象。数值分析结果进一步丰富对水平井射孔参数优化及水力压裂施工的研究。其次,鉴于页岩储层通常发育有大量的天然裂缝,对层状页岩储层中水力裂缝与天然层理的相互作用以及缝网的形成规律进行了数值模拟,借鉴水平应力差异系数初步分析体积压裂技术的效果,同时建立数值模型分析了地应力差、脆性指数、层理特征等因素对形成的压裂缝网复杂程度的影响,希望能对页岩储层压裂缝网形成的研究和设计提供些许参考。最后,依据目标储层实际情况对单井不同间距裂缝周围的应力分布及相互干扰现象进行了数值分析,对压裂裂缝间距进行优化选择,并进一步分析了两井同步压裂时压裂段裂缝的合理间距,在此基础上,综合评价了两种压裂方案。
[Abstract]:Affected by the low permeability of shale reservoir, shale gas (oil) reservoir needs hydraulic fracturing before it can be exploited. Because horizontal well has obvious advantages in increasing contact area with reservoir, reducing cost and having long-term stable production ability, it has been widely used in shale gas development, especially when cooperating with slippery water multistage fracturing. The effect of increasing production is more remarkable. Most fracturing operations take place after casing perforation, and the initiation of hydraulic fractures is closely related to the mechanical properties of shale rocks and the nonuniformity of shale reservoir mechanical properties. Therefore, the actual fracture initiation and extension after perforation completion is complex and diverse. In addition, a large number of natural fractures and bedding are often developed in shale reservoirs. Hydraulic fracturing of shale reservoirs can form large scale network fractures, which is the effect of normal volume fracturing. This paper is supported by the China Petroleum Science and Technology Innovation Fund (2013D-5006-0211), the National Natural Science Foundation of China (51479024) and the State key basic Research Program 973 (2014CB047103). Based on the understanding of hydraulic fracturing mechanism of rock mass described by predecessors, the seepage stress-damage model of hydraulic coupling action in fracturing process is set out, and it is realized in the finite element software RFPA percolation plate. The finite core physical experimental results are simulated and evaluated, and the experimental parameters related to the subsequent chapters are obtained, and the numerical simulation of the fracture initiation and propagation characteristics of horizontal well in shale reservoir is carried out. Firstly, numerical simulation of the initiation characteristics of directional perforating hydraulic fractures in horizontal wells is carried out, and a numerical model is established to analyze the effects of two factors: ground stress difference and perforation azimuth. The results show that hydraulic fractures may not occur at the perforation end. On this basis, the possibility and conditions of the formation of fracturing double fractures are further discussed. In addition, the phenomenon of the fracture extending to the interface between the production layer and the interlayer is simulated. The numerical analysis results further enrich the research on the optimization of perforation parameters and hydraulic fracturing operation of horizontal wells. Secondly, in view of the large number of natural fractures in shale reservoirs, the interaction between hydraulic fractures and natural beddings in layered shale reservoirs and the formation of fracture networks are numerically simulated. Using horizontal stress difference coefficient for reference, the effect of volume fracturing technique is preliminarily analyzed. At the same time, a numerical model is established to analyze the influence of factors such as ground stress difference, brittleness index and bedding characteristics on the complex degree of fracture network formed. It is hoped that this paper can provide some references for the research and design of the formation of fracture network in shale reservoir. Finally, according to the actual situation of the target reservoir, the stress distribution and interferences around the fractures with different spacing in single well are analyzed numerically, and the fracture spacing is optimized. On the basis of the analysis of the reasonable fracture spacing between the two wells during synchronous fracturing, two fracturing schemes are comprehensively evaluated.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE357.1

【参考文献】