NUMERICAL SIMULATION ON THE CHANGES OF ELASTIC WAVE VELOCITIES OF ROCKS UNDER RESERVOIR BOTTOM DURING WATER STORAGE AND DRAINAGE

doi:10.3969/j.issn.0253-4967.2014.02.004

Abstract

Abstract: In order to know to what degree can elastic wave velocity be influenced by effective stress changes in rock medium at the bottom of reservoir, and the quantitative relationship between changes of elastic wave velocity, pore pressure and effective stress during the process of reservoir water body load-unloading and water infiltration, pre-works have been done on the geological structures and hydrogeologic conditions in the Zipingpu reservoir, Sichuan Province, and its adjacent areas in detail, and a mathematical model was deduced which could describe rock-mass distortion and stability influenced by liquid seepage in porous rock media during the process of reservoir water body load-unloading and water infiltration. On this basis the paper makes a further study to establish a quantitative mathematical model to describe the relationship between elastic wave velocity and effective stress, and also taking Zipingpu reservoir as an example, calcutates the dynamic changes of pore pressure, additional elastic effective stress, and elastic wave velocity using finite element method. The simulation results show that: the change in incremental value of elastic wave velocity during the process of reservoir water body load-unloading and water infiltration is not obvious, the maximum amplitude is only about ±0.013 km/s, and changes mainly concentrate in local areas above 5km depth under the reservoir bottom. The change in incremental value of elastic wave velocity is associated with changes of additional effective stress, similar to reservoir water-level fluctuation in curve shapes. Incremental value of elastic wave is related to location, depth, and additional effective stress of different observation points. The velocity change of P-wave is greater than S-wave at the same observation point. The time sequence changes of elastic wave velocity obtained by this paper are generally similar to the relative velocity variations of the Zipingpu reservoir region obtained by other scholars using seismic ambient noise method, but the variation range is slightly different.

Key words: reservoir, additional effective stress, elastic wave velocities, numerical simulation

摘要： 为了解水库水体加、卸载及渗透过程中，库底岩石介质有效应力变化对弹性波速的影响，以及弹性波速变化与孔隙压力、有效应力变化之间的定量关系，以四川省紫坪铺水库为例，在前期已建立库区地质构造与水文地质结构模型，并推导出岩石介质变形与流体渗流耦合数学模型的基础上，进一步建立了有效应力对岩石弹性波速影响的数学模型，利用有限元方法定量计算了库底岩石介质的孔隙压力、附加有效应力和弹性波速的变化。结果表明：在水库水体加、卸载及渗透过程中，地下岩石介质弹性波速增量值的变化并不明显，最大变幅仅为±0.013 km/s，变化范围主要集中在库底5km以上的局部区域；弹性波速增量值与附加有效应力变化同步，与水库水位变化形态相似；不同观测点弹性波速变化量的大小与埋藏位置、深度及附加有效应力的变化幅度有关，同一观测点，弹性纵波波速变化幅度大于弹性横波波速。文中数值模拟的结果与一些学者通过环境噪声方法获得的紫坪铺水库附近区域相对波速变化的反演结果在变化形态上大体一致，但变化幅度略有差异。

关键词: 水库, 有效应力, 弹性波速, 数值模拟

CLC Number:

P315.72⁺3

ZHOU Bin, SUN Feng, XUE Shi-feng, JIANG Hai-kun, SHI Shui-ping. NUMERICAL SIMULATION ON THE CHANGES OF ELASTIC WAVE VELOCITIES OF ROCKS UNDER RESERVOIR BOTTOM DURING WATER STORAGE AND DRAINAGE[J]. SEISMOLOGY AND GEOLOGY, 2014, 36(1): 39-51.

周斌, 孙峰, 薛世峰, 蒋海昆, 史水平. 水库蓄放水对库底岩石介质弹性波速影响的数值模拟[J]. 地震地质, 2014, 36(1): 39-51.

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