矿井张量电阻率法理论基础研究

Theoretical foundation of tensor measurement for mine resistivity method

煤矿采掘活动诱发的局部和微观电各向异性特征时空演变规律有望成为煤矿动力灾害预测预报的新机制。张量电阻率测量是掌握和认识电各向异性特征的重要方法途径,煤矿井下具有开展张量电阻率测量的独特优势。在岩石电各向异性物理机制分析的基础上,结合煤矿井下实际,提出了适合煤矿井下条件的张量电阻率测量方法。以层状各向异性介质模型为例,采用模拟计算的方法对地层倾角、走向变化时的视电阻率方向特性进行了分析;建立了巷道底板岩溶发育全空间模型,从宏观电各向异性的角度分析和验证了电阻率测量所具有的方向性。研究结果表明,采动影响使煤岩体具有电各向异性特征,采动裂隙内的水气富集程度也对煤层横向和纵向电阻率产生明显影响;含水量越大,各向异性系数越高。受上覆和下伏地层电阻率影响,各向异性地层的张量电阻率幅值显示出层状地层的综合反映;其电阻率幅值与裂隙带倾角大小有关,不受地层走向影响,但视电阻率的椭圆分布会随地层走向而发生旋转,旋转的角度依赖于地层走向的变化。这说明采动岩体变形、破坏与流体运移必然会引起含煤地层电各向异性特征的规律性时空演变。通过实时动态测量煤岩体的张量电阻率,可以识别和发现因采掘活动、流体运移引起的局部、微观电各向异性特征。在应力峰值未到达之前,及时捕捉煤矿动力灾害孕育、发展的先兆信息,并在应力释放前的可逆阶段采取预防措施,可从源头上避免煤矿重大动力灾害的发生。

The law of temporal and spatial evolution of local or microscopic anisotropy,caused by coal mining,is a key study on coal mine dynamic disaster prediction and prevention.As an important approach to understand the anisotropic characteristics of coal and rock mass,the tensor resistivity measurement has unique advantage in underground mine roadway.Based on the analysis of physical mechanism for rock resistivity anisotropy along with underground roadway circumstances,a mine tensor resistivity method was proposed.Taking the examples of anisotropic layered medium models,the apparent resistivity was calculated with different stratigraphic dips and strikes,and the directional characteristics of which were analyzed.Using a full-space model with Karst development,the directionality of mine resistivity method was analyzed and verified from global anisotropic response view.The results show that it has an anisotropic behavior in coal and rock mass under the influence of mining,and the water-gas enrichment status in fracture has an effect on the horizontal and vertical resistivities.The anisotropic coefficient increases with water content.Apparent resistivity amplitude in an anisotropic stratum is affected by its overlying and underlying strata,which reflects a comprehensive response of all layers.Besides,the amplitude can be decided by the fracture zone dips instead of the strikes,however,the elliptic resistivity distribution rotates owing to the strikes change.The results also indicate that the regular temporal and spatial evolution of strata anisotropic behavior is influenced by rock mass deformation and failure,as well as fluid migration.By real-time dynamically measuring the tensor resistivity of coal and rock mass,the local or microscopic anisotropic characteristics caused by mining and fluid migration can be recognized.Capturing auspice signal containing dynamic disaster gestation and development in time before the peak stress arrives,and adopting prevention approach in reversible phase before stress releases,the significant dynamic disasters can be avoided from the source.