Surface-To-Borehole Tfem Data Acquisition System Development and Field Test

A surface-to-borehole time-frequency domain EM (TFEM) data acquisition system has been developed and a successful field test was conducted in the Liaohe Oilfield of North China early this year. The field test has successfully acquired downhole 3-component magnetic field and vertical electrical field surface-to-borehole TFEM data the first time using a 3 km long surface dipole current source at two source locations. The dipole current source injected square wave current into the subsurface to generate the underground TFEM signal. A newly developed 4-level borehole TFEM receiver array was used to record surface-to-borehole TFEM data from the depth of 1,000 m to 1,800 m in the borehole. Each level of borehole TFEM receiver contains a 3-component time domain induction coil package installed in the center of the receiver tool and two electrodes are located at each end of the receiver tool with a spacing of 10 m. The surface-to-borehole TFEM data show the characteristics of subsurface formation electromagnetic properties and their changes at different depth. The first field test proved the correct design of the surface-to-borehole TFEM data acquisition system and its ability to acquire high quality borehole TFEM data than that of the borehole-to-surface TFEM system.