砂岩微观孔隙特征及饱水度对纵波波速的影响研究

Study on the Influence of Microscopic Pore Characteristics and Water Saturation on Longitudinal Wave Velocity

为了研究不同饱水度与微观孔隙结构特征对岩样纵波波速的影响规律,选取两组不同微观结构特性的黔东南低渗砂岩为研究对象并对其进行了改进的断铅声发射试验及压汞试验,测试了纵波波速及孔隙体积特征。结果表明:不同组别内的砂岩孔隙具有多元性和单一度,第1组砂岩的大、中、小及微孔隙的多样度分别为37.37%、37.16%、36.16%、36%、35.23%、33.76%,而第2组砂岩的孔隙单一度分别为34.8%、39.2%、42.6%、52.6%。多样性岩样的纵波波速随饱水度增加呈"快速增加、稳态变化、急剧增加"三个变化阶段,其饱水度分界点分别为30%、70%。单一性岩样的纵波波速先缓慢减小后急剧增大,其饱水度分界点近似为75%。基于毛管模型以及单一孔隙试验的试验结果,建立了不同饱水度下砂岩微观孔隙结构特征与宏观纵波波速的关系方程,并与多样性砂岩进行对比分析,纵波波速的变化规律具有良好的一致性。研究成果对于揭示不同饱水岩体中的声波演化差异性特征提供一定理论参考。

In order to study the influence of different water saturation and microscopic pore structure characteristics on the longitudinal wave velocity of rock samples,two groups of Qiandongnan low-permeability sandstone with different microstructure characteristics were selected as the research objects and improved broken lead acoustic emission test and mercury injection test were carried out to test the characteristics of longitudinal wave velocity and pore volume.The results show that the sandstone pores in different groups are diversified and single,the diversity degrees of the large,medium,small and micro pore of first group are 37.37%,37.16%,36.16%,36%,35.23%and 33.76%,while the single degrees of the second group sandstone are 34.8%,39.2%,42.6%and 52.6%,respectively.The longitudinal wave velocity of diverse rock sample shows"a first rapid increase,then steady change,and finally sharp increase",with the boundary points of30%and 70%respectively.The longitudinal wave velocity of the single rock samples decreases first and then sharp increases and the filling with a boundary point is approximately 75%.Based on the test results of wool tube model and single pore test,the relationship between micro pore structure characteristics and macro longitudinal wave velocity is established,and compared with the variation of longitudinal wave velocity,and the change law of longitudinal wave velocity has a good consistency.The research results provide some theoretical reference for revealing the differences of acoustic wave evolution in different filled rock bodies.