On the pressure dependence of elastic parameters in porous and fractured rocks of the upper continental crust

在icdp项目“大陆断裂系统中的能量和流体输运”中，本项目致力于研究大陆上地壳各向异性弹性参数的应力和流体压力依赖关系。我们的项目包括两个方面：a)将压电敏感性方法扩展到裂缝各向异性介质，包括非线性弹性的影响，以及(b)将其应用于KTB岩心样品的实验室数据。这种方法建立了一套方程，可以根据多孔和裂缝性流体饱和岩石的压缩性和孔隙度来解释速度与压力数据。这是为数不多的理论方法之一，可以根据岩石物理参数直接解释地震速度的应力依赖性。此外，它还引入了额外的，甚至在某种程度上扩展了新的岩石特性，如压电性、刚性和柔顺性孔隙度。KTB深部实验室的136个岩心样品可在高达350兆帕或更高的压差范围内测量各向异性弹性速度和整体变形。这些数据将根据各向异性压电敏感性方法进行分析和重新解释。这将使我们更深入地了解KTB岩石在原位张拉应力状态下的应力相关弹性各向异性。这可能有助于解释和预测由于上大陆地壳岩石孔隙流体压力的变化而可能引起的各向异性变化。

Within the ICDP-Program "Energy and Fluid Transport in Continental Fracture Systems" this project is dedicated to the stress and fluid pressure dependency of anisotropic elastic parameters in the continental upper crust. Our project follows two aspects: a) the extension of the piezosensitivity approach towards fractured anisotropic media including effects of nonlinear elasticity and (b) its application to laboratory data from KTB core samples. This approach establishes a set of equations which allow to interpret velocity vs. pressure data in terms of compressibility and porosity of porous and fractured fluid saturated rocks. It is one of the very few theoretical approaches allowing a direct interpretation of the stress dependency of seismic velocities in terms of rock physical parameters. Furthermore, it introduces additional and to some extend new rock characteristics, like the piezosensitivity and stiff and compliant porosity. Measurements of anisotropic elastic velocities and bulk deformation over a differential pressure range up to 350 MPa and higher are available for a set of 136 core samples from the KTB deep laboratory. These data will be analyzed and reinterpreted in terms of the anisotropic piezosensitivity approach. This will give a closer insight into the stress dependent elastic anisotropy of the KTB rocks under the in situ tensorial state of stress. It might help to explain observed and to predict possible anisotropy changes due to changes of pore fluid pressure in the rocks of the upper continental crust.