摘要：

天然页岩样品矿物组成复杂、沉积环境和成熟度差异较大，难以单独揭示有机质成熟演化对岩石物理影响的控制作用。本文基于人工模拟实验方法，在保持矿物组成和有机质含量一致的条件下，制备3种热演化程度的人工页岩样品，采用扫描电子显微镜(SEM)、核磁共振(NMR)以及低温液氮吸附实验观测不同热演化阶段样品的孔隙度和孔隙微观结构；在压力条件下对样品的3个方向进行超声波速度测试，分析有机质结构变化对孔隙特征及弹性响应的影响及相互间的关系。实验结果表明，随着热演化程度增加，样品孔隙度呈先增加后略有降低的变化，成熟阶段总孔隙度最大，过成熟阶段总孔隙度略有降低；随着热演化程度增加，样品中有机质微孔逐渐发育，微孔占比增加。在低围压成熟阶段样品的纵波速度和横波速度变化最明显，不同热演化程度样品之间的速度差异随围压增加逐渐减小；在45°方向3种阶段的纵、横波速度差异较明显，在高围压成熟和过成熟阶段纵、横波速度趋于一致。热演化过程改变了样品内部有机质孔隙的微观结构，致使在低围压时成熟阶段的非均质性增大，高围压时成熟和过成熟中的微孔闭合各向异性参数几乎相同。本实验方法为了解天然页岩热演化过程对储层弹性的影响提供了一种有效的研究途径。

关键词: 人工岩样, 岩石物理, 成熟度, 孔隙度, 各向异性, 声波速度

Abstract:

Natural shale samples usually exhibit complex mineral compositions, variable depositional environments, and significant differences in thermal maturity, making it difficult to independently identify the controlling effects of organic matter maturation on rock physical properties. In this study, an artificial simulation approach was adopted to prepare three types of artificial shale samples with different thermal evolution stages while maintaining consistent mineral compositions and organic matter contents. Scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and low-temperature nitrogen adsorption experiments were conducted to characterize the porosity and microscopic pore structures of the samples at different thermal evolution stages. Ultrasonic velocity measurements were performed along three directions under confining pressure conditions to investigate the influence of organic matter structural evolution on pore characteristics and elastic responses, as well as their interrelationships. The experimental results indicate that, with increasing thermal maturity, the porosity of the samples first increases and then slightly decreases. The mature sample exhibits the highest total porosity, whereas the over-mature sample shows a slight reduction in total porosity. With increasing thermal maturity, organic-matter micropores gradually develop, resulting in an increasing proportion of micropores in the samples. Under low confining pressure conditions, the mature sample exhibits the most significant variations in both P-wave and S-wave velocities. The velocity differences among samples with different thermal evolution stages gradually decrease with increasing confining pressure. In the 45° direction, noticeable differences in P-wave and S-wave velocities are observed among the three maturity stages, whereas the velocities of mature and over-mature samples become nearly identical under high confining pressure conditions. Thermal evolution modifies the microscopic structure of organic matter-hosted pores within the samples, resulting in enhanced heterogeneity of the mature samples under low confining pressure conditions. At high confining pressures, the closure of micropores in mature and over-mature samples leads to nearly identical anisotropy parameters. This experimental approach provides an effective method for understanding the influence of organic matter thermal evolution on the elastic properties of natural shale reservoirs.

Key words: artificial shale, rock physics, thermal maturity, porosity, elastic anisotropy, ultrasonic velocity

中图分类号: 

• P618.13

• TE135