Topographic effects on long offset transient electromagnetic response

The forward modeling procedure used in this article is formulated with the volume integral equation based on the tensor Green＇s function. The electromagnetic components responses are first calculated in the frequency domain and then transformed to the time domain by digital filtering. The valley and hill topography with a layered earth is stimulated by a horizontal electric dipole （HED） transmitter, which is common in field surveys, and the TEM responses are calculated at the transmitter and receivers. The topography effects on the long offset electromagnetic transient （LOTEM） responses are discussed in detail. The results show that both valley and hill topography has significant effect on the LOTEM measurement. If the HED is located in the bottom of a valley, the distortion of the observed anomalous field at distance is severe. A valley at the receiver locations show a strong effect but are localized in space and time. In general, hill-shaped topography shows smaller effects no matter where its located. When the topography is located between source and receivers, the influence is negligible. We conclude that the location of the source is much more important than the receivers and it is critical to put the transmitter in an open flat area in the field survey.

强富水复杂区域裂隙导水通道探查技术研究

汾源煤业5号煤层下距奥灰约63 m,奥灰含水层富水性较强,为5-103工作面主要直接充水含水层。工作面掘进期间揭露的断层较多,构造复杂,存在奥灰水通过构造与工作面底板发生联通的可能性。为防止工作面下部灰岩水沿构造裂隙带上涌造成出水事故,使用直流电法测深、瞬变电磁测深法等手段,对工作面下部砂岩及奥灰的富水特征和断层的含导水特征进行综合探测,以便制定正确的防治水措施,确保工作面安全回采。