页岩气藏压裂岩体突变特征及多重分形缝网逾渗演化研究

The main means for developing shale gas reservoir is hydraulic fracturing technology. The hot issues discussing in the world is map cracks fracturing, and the formation of map cracks and the connection character of the rock body are the key issue of this study. However, due to the complexity of brittleness and plastic characteristics for shale gas rock, and the existing of multiple levels of mesoscopic micro-scale natural cracks, the formation of map cracks and the connection regulations are complex. It has great value for shale gas efficient development if the mechanics behavior of fracturing rock, fracture network evolution and connection regulation can be described accurately. In this project, the issue of map cracks formation and connection for shale rock was studied for the first time basing on nonlinear dynamics and percolation theory. The multi-fractal description method of multilevel mesoscopic micro-scale three-dimensional map cracks structure was put forward, and the percolation system of three-dimensional multi-fractal map cracks structure was built. The discrimination criteria of hydraulic fracture inducing cracks evaluation for different brittle plastic shale rock were proposed basing on catastrophe theory. Three-dimensional multi-fractal map cracks percolation system evaluation model was built basing on catastrophe theory by studying the map cracks connection conditions and main control factors of percolation system evaluation. By the study of this project, the physical connotation and essential characteristics of map cracks evaluation and the formation of connecting channels for shale gas reservoirs were revealed. The study content is a frontier subject at home and abroad. The research achievements can fill the gaps in the field, which can provide reliable scientific guidance for the effective follow-up development of shale gas reservoirs.

压裂技术是页岩气藏开采的主要手段。缝网压裂是国际上探讨的热点问题，其中岩体压裂缝网形成与连通特征是其研究的核心。然而，由于页岩岩体脆塑性特征复杂且存在多级介观微尺度天然孔裂隙，致使页岩气藏压裂缝网形成与连通规律复杂。若能准确地描述页岩岩体压裂力学行为及裂缝网络演化与连通规律对页岩气高效开发具有重大价值。本课题首次基于非线性动力学与逾渗理论研究页岩岩体压裂缝网形成与连通问题，提出了岩体多级介观微尺度三维缝网结构的多重分形描述方法，构建三维多重分形网络结构逾渗体系；基于突变理论提出不同脆塑性页岩岩体压裂破裂诱导孔裂隙发生演化的判别标准。开展逾渗体系演化网络连通条件与主控因素研究，建立基于突变理论的三维多重分形网络逾渗体系演化模型。课题研究揭示了页岩气藏压裂缝网演化与连通通道形成的物理内涵与本质特征。课题内容在国内外属前沿课题，研究成果能够填补国内外空白并为页岩气藏后续高效开发提供可靠科学指导。

压裂技术是页岩气藏开采的主要手段。缝网压裂是国际上探讨的热点问题，其中岩体压裂缝网形成与连通特征是其研究的核心。然而，由于页岩岩体脆塑性特征复杂且存在多级介观微尺度天然孔裂隙，致使页岩气藏压裂缝网形成与连通规律复杂。若能准确地描述页岩岩体压裂力学行为及裂缝网络演化与连通规律对页岩气高效开发具有重大价值。本课题研究内容主要有一下三个方面：页岩储层介观孔裂隙三维多重分形网络逾渗系统构建与仿真、页岩压裂介观孔裂隙三维网络损伤演化非线性动力学特征研究以及页岩气藏压裂介观孔裂隙三维多重分形网络体系逾渗演化研究。基于逾渗理论推导页岩岩体损伤破裂突变模型，通过CT扫描实验，运用MATLAB得到页岩样品的孔裂隙多重分形谱函数及各多重分形参数，建立三维孔裂隙双重介质逾渗模型。建立了孔裂隙双重介质逾渗概率统计方法。开展岩石力学参数实验，建立并推导岩体非线性损伤力学模型，并进行了有限元模拟验证模型。开展不同矿物含量页岩室内水力压裂实验，建立并推导页岩损伤破裂的折迭突变模型。课题研究揭示了页岩气藏压裂缝网演化与连通通道形成的物理内涵与本质特征。该课题的研究对目前的页岩岩体压裂裂缝缝网系统的本质规律描述具有重要意义。为页岩气藏缝网压裂的研究开辟了新思路与研究方法。

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