多尺度多场耦合作用下页岩气藏体积压裂水平井非线性渗流理论研究

Shale gas reservoirs have complex pore structure and multi-scale pore-size distribution, together with multi-field coupling effect during the production of shale gas, causing gas flow in shales is controlled by multiple mechanisms, including conventional viscous flow, desorption from the surface of organic matter, as well as fluid-solid coupling non-linear flow. Existing seepage theory does not take into consideration all the mechanisms. In addition, most current research simplifies hydraulic fracturing induced fracture networks in shale gas reservoirs as several discrete fractures, which is not the case for shales. Based on experimental study of complex pore structure in shales and the investigation of coupling mechanisms of stress field, seepage field and concentration field during shale gas production, this project will figure out multiple flow patterns of shale gas in multi-scaled pore spaces. This project will also try to present a reasonable model to represent complex fracture network created by hydraulic fracturing, and a comprehensive mathematical model will be established to describe shale gas flow in SRV fractured horizontal wells in multi-scaled shale gas reservoirs with consideration of multiple mechanisms. The characteristics of transient pressure dynamics and production decline for SRV fractured horizontal wells in shale gas reservoirs will be analyzed, and the effects of relevant parameters will be discussed and ranked, and optimal shape of fracture networks will be proposed. This project has both theoretical and practical significance to the optimization of hydraulic fracturing and efficient development of shale gas reservoirs.

页岩孔隙空间的多尺度性和开采过程中应力场、渗流场和浓度场的相互耦合作用，决定了页岩气渗流机制的复杂性和多样性，储层中既存在常规渗流，又伴随着解吸、扩散、流-固耦合渗流等特殊流动机制，而现有渗流模型未能全面考虑页岩气多重流动机制的耦合作用。此外，对于页岩气藏水平井体积压裂形成的复杂缝网，国内外现有研究也大多集中在单条或数条简单裂缝方面，针对复杂缝网系统的渗流理论研究则鲜有所见。本课题拟在弄清页岩孔隙结构特征的基础上，探讨页岩气开采过程中应力场-渗流场-浓度场耦合作用机制，揭示多尺度流动空间内页岩气多重流动规律，合理描述页岩体积压裂后形成的裂缝网络，科学地建立起多尺度、多机制、多场耦合渗流理论模型并求解，并对页岩气藏压裂水平井不稳定压力动态和产量变化规律进行分析，形成多尺度多场耦合页岩气藏压裂水平井不稳定试井和产能预测方法，构建页岩气藏体积压裂缝网参数优化体系，为页岩气的高效开发提供理论支撑。

页岩储层微观孔隙结构的复杂性及多尺度性以及特殊的气体储集方式，导致页岩气在储层中的流动受解吸、扩散、粘性流等多种机制的控制，使得页岩气藏的开发远远难于常规气藏，常规气藏渗流理论不能直接应用于指导页岩气藏开发。要对页岩气藏开发动态进行准确预测，就需要对页岩气在储层中的复杂渗流规律进行研究。本课题结合室内实验对页岩储层微观孔隙结构、页岩气吸附-解吸规律、应力敏感效应及多重运移机理进行了研究，建立了四类不同的页岩气藏基本渗流物理模型。并以四类页岩气藏基本渗流模型为基础，采用源函数理论，针对页岩气藏中无限导流多级压裂水平井、有限导流多级压裂水平井、存在SRV区域的页岩气藏有限导流多级压裂水平井建立了六类不稳定试井模型及三类非稳态产能模型。而后利用Laplace变换、摄动理论等数学物理方法对模型进行了求解，并基于求解结果编程绘制了页岩气藏多级压裂水平井不稳定试井样板曲线和非稳态产能变化曲线，结合曲线特征分析了地层中特征流动阶段，探讨了页岩气吸附-解吸、扩散、压裂主裂缝相关参数（裂缝条数、间距、半长、导流能力等）、压裂缝网相关参数（SRV区域大小、SRV区域缝网渗透率）、页岩储层应力敏感效应以及气藏相关参数对不稳定压力动态及非稳态产能变化规律的影响，明确了影响页岩气藏压裂水平井生产动态的主要参数。本课题研究成果可用于获取页岩气井及储层相关动态参数及气井非稳态产能计算，所得到的规律性认识也可为页岩储层压裂施工设计提供指导，并最终为指导页岩气藏高效开发提供理论依据。