矿井可控源电磁法三维数值模拟

Mine security problems caused by deep resource mining are getting increasingly serious. The mine electromagnetic prospecting methods used by now are inefficient, easily disturbed, and with incomplete data interpretation system, when been applied to detect the underground hidden disastrous geological structure. Moreover, the methods are facing bottlenecks in the development becase of lacking of basic theoretical research. Controlled-source electromagnetic method shows big depth of prospecting, high resolution, and high efficiency in both ground and marine prospecting, which suggests its potential capability of detecting the underground hidden disastrous geological structure. In this project, 3D numerical modeling for mine controlled-source electromagnetic method is carried out. Focused on electromagnetic field produced by electric dipole in frequency-domain, the primary field is calculated by fast Hankel transforms, the boundary value problem derived from the second field is discretized by staggered-grid finite difference method. Multigrid method is applied to solve the large linear equation system coming from the discretization.The final electromagnetic solution is turned into wide-band apparent resistivity for analysis of relationship between frequency and survey depth.Whole space effect, layered medium, and tunnel influence are taken into consideration during modeling. A large amount of numerical work is carried out, mainly focusing on the typical mine electrical models, such as gob area, collapse collum, fault zone, fracture zone and so on, to achieve the regularity understandings which could be used for the guiding of field work.The study in this program will build up theoretical basis for the application of controlled-source electromagnetic method in mine prospecting, and moreover ,it will suggest a brand-new way for the mine geological security control.

深部矿产资源开采导致的矿井安全问题日益突出,现有矿井电磁勘探方法在探查地下隐伏灾害性地质构造时存在施工效率低、抗干扰能力差、数据解释方法不完善等诸多问题，并由于缺乏基础理论研究遭遇发展瓶颈。可控源电磁法在地面和海洋勘探中表现出勘探深度大、分辨能力强、观测效率高等特点，具备探查地下隐伏灾害性地质构造的潜力。项目开展矿井可控源电磁法三维数值模拟，针对频率域电偶源激发的电磁场，采用快速汉克尔变换计算一次场，二次场边值问题采用交错网格有限差分法进行离散，离散所得大型线性方程组采用多重网格法进行求解，并根据广义视电阻率分析频率与探测深度的关系。同时考虑全空间效应、层状介质以及巷道影响等，建立采空区、陷落柱、断层及裂隙密集带等典型矿井地电模型，通过大量模拟计算获得可应用于指导实际生产的规律性认识。项目研究可为频率域可控源电磁法在矿井勘探中的应用奠定理论基础，并为矿井地质安全保障提供一种新的思路和方法。

深部矿产资源开采导致的矿井安全问题日益突出，可控源电磁法在地面和海洋勘探中表现出勘探深度大、分辨能力强、观测效率高等特点，具备探查地下隐伏灾害性地质构造的潜力。项目针对矿井可控源电磁法三维数值模拟，采用滞后卷积快速汉克尔变换实现了一次场的数值计算，采用交错网格有限差分法实现了二次场边值的离散，引入预处理矩阵实现了适用于求解可控源电磁法三维数值问题的预条件复型代数多重网格算法，通过求解泊松方程实现了磁场分量的散度校正，采用二分法实现了各电磁场分量广域视电阻率的数值计算，完成了矿井可控源电磁法三维正演程序。通过对比全空间三层模型的数值解与解析解，验证了程序的正确性。通过分析半空间和全空间的解析解发现，当工作面埋深超过400m时，即可适用全空间假设。通过分析巷道掌子面尺寸、巷道长度、电偶源位置以及频率等参数变化时的巷道影响发现，当接收点距离掌子面超过5m时，比值法校正后的视电阻率误差可降至2%以下。通过分析全空间三层模型在不同收发距下随频率变化的广域视电阻率曲线发现，当收发距r≥200m时，通过频率测深可以识别浅部的低阻层。通过分析全空间立方体模型在不同接收点和不同频点的广域视电阻率曲线发现，矿井可控源电磁法的有效工作频率范围为10Hz~104Hz。通过分析不同埋藏深度含/导水构造的广域视电阻率剖面发现，含/导水构造的埋藏深度越大，低阻中心区域对应的频率越高。通过对典型矿井地电模型进行模拟计算，获得了煤矿井下典型含/导水构造在水平位置、埋藏深度、尺寸以及电阻率变化时的异常响应特征，分析了矿井可控源电磁法对多个异常体的探测识别效果和层状介质对探测结果的影响，为矿井可控源电磁法在实际生产中的应用提供了理论指导。