饱水过程中类岩石材料波速和电阻率变化规律及其相互关系试验研究

EXPERIMENTAL RESEARCH ON WAVE VELOCITY AND ELECTRICAL RESISTIVITY OF ROCK-LIKE MATERIAL DURING SATURATION PROCESS

研究饱水过程中岩石波速和电阻率变化规律及其相互关系,对实际工程中岩石物性判断和地球物理探测资料综合分析解释具有重要意义。为防止原岩试样的矿物组成、原生裂隙等其他因素对试验结果的影响,采用水泥砂浆制作30组孔隙率不同的类岩石材料试样,系统测试饱水过程中不同试样的波速和电阻率变化情况,分别揭示波速和电阻率随饱和度、孔隙率的变化规律。采用常用的基于Wood理论假设的Gassmann方程得到波速与饱和度、孔隙率的理论关系,但与试验实测结果相比,该理论关系不能较好地描述饱水达到门槛值之后波速快速上升的特征。对此,考虑重力等影响对试样中孔隙水的分布状态做出合理假设,修正饱水全过程中波速与饱和度、孔隙率的关系式,与试验实测数据变化特征较一致。同时采用Archie的非饱和岩石电阻率模型公式对电阻率随饱和度和孔隙率变化规律进行了较好拟合。在此基础上,针对以往波速与电阻率关系研究中仅以孔隙率为纽带的问题,综合考虑孔隙率和饱水状态对波速–电阻率变化规律的影响,建立以试样孔隙率和饱水状态为桥梁的波速–电阻率关系,与试验实测数据拟合较好,并通过石灰岩原岩试样测试验证其合理性。

The wave velocity and electrical resistivity and their relationship of rock materials during the saturation process are important for the judgment of rock physical properties,the comprehensive analysis and interpretation of geophysical data and so on. However,the mineral composition,the existing fissures and other factors of the rock sample often affect the experimental results. In order to prevent these influences,cement mortar was used to make 30 rock-like samples with different porosities. The wave velocity and the electrical resistivity for different samples were measured to reveal the variation of wave velocity and the electrical resistivity with the degree of saturation and porosity. A mathematical formula describing the wave velocity,the degree of saturation and the porosity was obtained by applying Gassmann equation based on the theoretical assumption of Wood. Compared with the test results,however,the formula fails to describe the characteristics of wave velocity rising rapidly after the saturation degree reaches a threshold value. Based on an assumption considering the gravitational effect on the distribution of pore water in the sample,An improving formula was put forward,which is consistent with the experiment data. Meanwhile,the resistivity varying with the degree of saturation and the porosity was fitted with the formula for unsaturated rock resistivity by Archie. In the past,the relationship between the wave velocity and the resistivity was established through the porosity only. The influence of porosity and saturated state were taken into account to establish the relationship between the wave velocity and the resistivity in this study. The established relationship fit the experimental data better and was validated in the experiment with the protolith of limestone.