煤矿井下随钻测量电磁传输信道建模

煤矿井下随钻测量系统目前主要采用有线方式进行信号传输,但是存在通缆钻杆加工技术要求严格、使用成本高等缺点,研制适用于煤矿井下的电磁波随钻测量系统十分必要。与地面钻进中井下-地面电磁传输信道不同,煤矿井下电磁波随钻测量采用孔内-孔口电磁传输信道,电磁信号传输过程中衰减特性亟待研究。基于经典电磁理论,结合煤层及煤层围岩电性,运用等效传输线法,计算了孔口接收电极间信号电压,包括煤岩层导电性、发射信号频率、钻杆电阻率、钻杆长度对接收信号电压的影响。仿真结果表明,相同工作条件下,煤矿井下孔口电极接收电压小于地面电极接收电压,大于地面电极接收电压一半。

Modeling an EM channel for MWD in underground coal mine

Currently the wired MWD in underground coal mine has many disadvantages over the wireless MWD,such as the strict demand of precision manufacturing process and high cost of usage.It is necessary to develop EM-MWD applied in underground coal mine.A downhole-to-roadway communication channel for horizontal drilling in underground coal mine,which is different from downhole-to-surface communication channel,was investigated in this paper.Based on the classical electromagnetic theory and electrical properties of coal strata,the received signal voltage between electrodes in the roadway was computed by using the equivalent transmission line method.The effects of the relevant parameters,such as the electrical conductivity of coal strata,operating frequency,the length and resistivity of the drill string were included.Simulation results show that the received signal voltage between electrodes in the roadway is less than that on the surface，but greater than half of that on the surface in the same condition.