基于饱和度和不同尺度的湖相页岩力学响应机理研究

Geomechanics properties are the key parameters for the brittleness and toughness characterization in shale oil-gas reservoirs, also the main factors in predicting favorable exploitation areas. Shale reservoirs present complex mineral composition, multiple microstructure and various pore types at micro- and nano-meters, leading to different geomechanical properties at multi-scales. In addition, shale reservoir is influenced by saturation due to high water content in situ. Focusing on the Triassic lacustrine shale reservoir in Ordos Basin, this project intends to reveal the differences in the micro-nano mechanical properties of shale under dry-to-full saturation conditions, influenced by the associated effect of clay mineral swelling. The research will identify the geomechanical properties of shale minerals through XRD, pyrolysis, high resolution scanning electron microscopy and energy spectrum elemental analyses. The macro-mechanical properties of shale samples with five levels (from dry to full) of saturation will be conducted by NMR and ultrasonic (P- and_S-waves) experiments, to analyze the response mechanism of geomechanical parameters for two-phase saturation and the main controlling factors at different scales. The overall results will deepen the understanding of geomechanical response mechanism of lacustrine shale reservoirs, and provide a theoretical basis for effective fracturing exploitation.

岩石力学特征是表征页岩储层脆–韧性的关键参数，也是油气开发有利区预测的主要因素。页岩储层矿物组成丰富、微观结构复杂、微纳米孔隙类型多样且受有机质含量和成熟度的影响，因此在多尺度上展示不同的力学特征。油气储层包含大量的地层水，页岩的力学特征还和饱和度存在密切的关系。本项目以鄂尔多斯盆地三叠系湖相页岩储层为对象，结合X衍射、岩石热解、高分辨率扫描电镜和能谱分析确定页岩中各矿物的力学特征，通过纳米力学实验探索干燥和饱和状态下页岩的微纳米力学特征之差异以及粘土矿物遇水膨胀对力学参数的影响，再结合物理声波分析骨架的力学响应机理，应用核磁共振和超声波（纵、横波）试验评估从干燥到饱和五种不同含水程度页岩样品的宏观弹性力学特征，探析湖相页岩双相流饱和度的弹性力学参数响应机理，以及页岩力学特征在不同尺度下的主控因素。本项目的研究成果将增强湖相页岩储层岩石力学响应的机理性认识，为有效的压裂开采技术提供依据。

岩石力学性质是指反映岩石应力-应变关系的变形特征和岩石破坏条件下最大应力的强度特征数据，对于页岩油气藏勘探与开发是至关重要的。因此本研究首先开展全岩矿物X衍射、岩石热解、扫描电镜、薄片分析和三轴力学实验，结合实验分析测定结果，分析了页岩储层矿物组成、微观结构特征；揭示了湖相页岩不同尺度的矿物组成类型、有机质含量的岩石力学响应机理以及主控因素；对压裂后的样品进行三维CT扫描，确定了压裂后样品裂缝展布特征及其影响因素；开展扫描电镜和微纳米力学实验，分析湖相页岩微观尺度上矿物形态、微观孔隙结构的岩石力学响应机理，及微观岩石力学的主控因素；又剖析了干燥和饱和两种状态下湖相页岩微观力学特征，发现页岩饱和后由于粘土矿物膨胀导致微观杨氏模量大大降低；最后，分别测试了不同饱和状态下页岩的弹性力学特征，也发现随着饱和度增高会大大降低纵横波的传播速度，同时湖相页岩的剪切模量和杨氏模量也会随之减小，其主要原因是由于泥页岩饱和水后粘土矿物发生膨胀导致岩石易发生形变，此研究成果可为后期湖相页岩储层水利压裂开发评价提供有效的理论依据。