有机质含量对页岩声波传播特性的影响

Influence of organic content on acoustic wave propagation characteristic of organic-rich shale

有机质是含气页岩的重要组分之一,有机质含量及类型在相当大程度上控制着页岩的孔隙度及含气性。前人工作多关注页岩矿物组分及其赋存方式所导致的声速及力学性质各向异性方面,而对有机质含量与页岩声波传播响应特性的关系则很少研究。以鄂尔多斯盆地三叠系延长组长7段富有机质页岩为研究对象,利用自行研制的SCMS-J型声电测试仪,采集15MPa围压下页岩纵/横波传播信息,分析有机质含量对纵/横波传播速度及页岩力学性能的影响,并运用快速傅里叶变换对采集的岩样声波波形数据进行频谱分析。研究表明:(1)纵/横波传播速度随着有机质含量增加而减小,纵/横波波速比随着有机质含量增加而增大;(2)页岩动态剪切模量G、动态体积模量K和动态弹性模量E随着有机质含量增加而降低,而泊松比v随着有机质含量增加而增大;(3)有机质含量越高,高频部分吸收越明显,主频向低频移动,形心频率f_c大小与有机质含量呈负相关。研究成果对基于声波测井信息评价页岩有机质含量及含气性具有一定的借鉴意义。

As the significant component of the gas-bearing shale, the content and type of organic control the porosity and hydrocarbon to a large degree.In the predecessors＇ work had been paid on the shale＇s velocity and mechanical properties anisotropy, caused by shale＇s mineal composition and arrangement anisotropy, while the research on the relationship of organic content and wave propagation characteristic of organic-rich shale was rare.The Chang 7 member of Triassic Yanchang Formation organic-rich shale in Ordos Basin is the object of our research. The information of ultrasonic wave under 15MPa confining pressure was ac- quired,with the assistant of the SCMS-J equipment developed in-house. The influence of organic matter content on wave propagation speed and mechanical properties of shale was analyzed.Rules of wave form and wave spectrum were researched using fast fourier transform. The following conclusions can be drawn. Firstly,Both compressional and shear wave velocities decrease as organic content increases.The impact of organic content on shear velocity was found to be more significant compared with the response with com- pressional velocity. Secondly, Both dynamic shear modulus （G）, dynamic bulk modulus （K）, dynamic Young ~ s modulus（E） decrease as organic content increases.Poisson ~ s ratio （v） increases as organic con- tent increases.The more organic content the shale ＂softer＂. Lastly, the higher organic matter content, the high frequency absorption is more obvious, the dominant frequency move to low frequency. Centroid fre- quency is negatively correlated with organic content.The results of this study have some guiding signifi- cance for the prediction of organic matter content by acoustic wave information.