瞬变电磁勘探中的低阻层屏蔽问题

Study on screening of conductive bed in transient electromagnetic prospecting

分析了华北型煤田地层的电阻率特点, 用时域有限差分法和G-S算法分别对理论模型和皖北煤电集团公司任楼煤矿的勘探实例作了数值与解析分析, 证明低阻层对瞬变电磁探测是屏蔽层, 当低阻层覆盖在探测目标之上时, 要探测同样的深度需更长的观测时间, 由此降低了晚期信号的信噪比, 因此现场施工应选择合理的设计参数并有必要研制用于煤田水文地质勘探的大功率仪器.

Analyzed resistivity characteristics of stratum in Huabei coal field,and established numerical analysis by finite-difference time-domain method for two-dimensional transient field excited by a negative step pulse and analytic analysis by G-S method for a prospecting example in the Renlou Mine, Wanbei Coal and Power Group Co., LTD. The theoretical research and numerical calculations indicated that the conductive bed is screening to transient electromagnetic field, the longer time is needed to detecting the same depth where conductive overburden exists and a decrease in transient fields for conductive overburden. Therefore, it is very important to choose from suitable parameters in transient electromagnetic prospecting,and develop a transient electromagnetic instrument with high power.