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

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。

EXPERIMENTAL RESEARCH ON ROCK-LIKE MATERIAL DURING SATURATION PROCESS FOR THE CHANGE REGULARITY OF VELOCITY AND ELECTRICAL RESISTIVITY AND THE INTERRELATION BETWEEN THEM

Research on rock materials during saturation process for the change regularities of velocity and electrical resistivity and the interrelation between them is significant in practical engineering，such as the judgment of rock physical properties，the comprehensive analysis and interpretation of geophysical data and so on. However，mineral composition，existing fissures and other factors of the rock sample often affect the experimental results. In order to prevent these influences，cement mortar is used to make 30 rock-like samples with different porosity. The changes of velocity and electrical resistivity for different samples were tested to reveal the change regularities of velocity and electrical resistivity with saturation and porosity. The theoretical formula among wave velocity，saturation，porosity is obtained by applying Gassmann equation based on the Wood theoretical assumption，but compared with the test results，it cannot describe the characteristic of wave velocity rapidly rising after the saturation reaches threshold value. A reasonable assumption considering the gravity effect to the distribution of pore water in the sample is made，the formula among wave velocity，saturation，porosity in the saturation process is modified，and it is nearly in accordance with the change characteristics of experiment data. Meanwhile Archie formula of unsaturated rock resistivity model is well used to fit the change rule of resistivity varying with saturation and porosity. On this basis，according to the problem that the past relationship between wave velocity and resistivity only consider porosity，the influence of porosity and saturated state is taken into account，and the relationship between wave velocity and resistivity is founded using porosity and saturated state as a bridge. It can provide a better fit to the real data，and the rationality is validated through experimentation with the protolith of limestone.