Electromagnetic data acquisition system for removing near surface effects from borehole to surface electromagnetic data

A method for removing near surface or shallow effects from borehole to surface electromagnetic data and/or surface to borehole electromagnetic data collected by an electromagnetic data acquisition system, including an electromagnetic source, an electromagnetic receiver and a controller, for measuring subsurface structures or fluids, said method comprising:

• deploying the system in an area of interest;
• activating the electromagnetic source to generate low frequency signals that affect the shallow, deep measurement data and high frequency signals that affect the shallow measurement data and combine the low and high frequency signals into a dual waveform;
• measuring, with the electromagnetic receiver, shallow measurement data produced by the high frequency signals and shallow and deep measurement data produced by the low frequency signals;
• removing the shallow measurement data from the shallow and deep measurement data to establish deep measurement data;
• and
• analyzing, with the controller, the deep measurement data to characterize and/or map and/or monitor the deep structures and/or fluids.

An electromagnetic data acquisition system for measuring subsurface structures with electromagnetic fields and for removing near surface effects from borehole to surface electromagnetic data and/or surface to borehole electromagnetic data, said system comprising:

• an electromagnetic source adapted to be operated at a depth in a borehole formed in the Earth's surface and for generating electromagnetic signals which interact with the subsurface structures and affect the electromagnetic fields;
• an electromagnetic receiver adapted to detect the electromagnetic fields and produce data representative of the electromagnetic fields;
• and
• a controller connected to the source and receiver and configured to:
• activate the source to generate a first electromagnetic signal that primarily illuminates shallow structures and a second electromagnetic signal that is more powerful and has a greater amplitude than the first electromagnetic signal and illuminates both shallow and deep structures;
• measure, with the receiver, shallow measurement data produced by the first electromagnetic signal and shallow and deep measurement data produced by the second electromagnetic signal;
• remove the shallow measurement data from the shallow and deep measurement data to produce deep measurement data;
• and analyze the deep measurement data characterize and/or map and/or monitor the deep structures and/or fluids.