DC resistivity methods can reliably detect resistivity contrasts from the near-surface to depths of 500-600 m. The resistivity of soils and rock is measured as a function of depth and of position. Porosity, permeability, ionic content of the pore fluids, clay content and facies are characterized by such measurements. In particular, we use electrical resistivity methods to highlight facies and thus to estimate velocity variations in the shallow part of the subsurface.
In a shallow water environment, where refraction (LVL) and uphole surveys costs are prohibitive, the near-surface velocity model can be derived using a towed resistivity streamer survey. The near-surface velocity model obtained by converting the resistivities into velocities can then be used to compute the static corrections.
Time-domain and frequency-domain electromagnetic techniques can reliably detect conductivity contrasts in the ground from the near-surface to depths of greater than 500 m. They are widely used for near-surface imaging, mineral exploration, water exploration, geological mapping, delineation of subsurface contamination plumes and salinity mapping.
With advances in instrumentation, processing and modeling, MT has become a very important tool in deep subsurface reconnaissance. Magnetotelluric services aim to image the Earth’s subsurface by measuring natural variations in electrical and magnetic fields at the Earth’s surface, ranging from very shallow depths by recording higher frequencies(Audiomagnetotelluric or AMT), down to depths of 10,000 meters by recording low frequencies (Magnetotelluric or MT). Under conductive overburden, MT provides unique penetration. Our AMT and MT services include high-quality data acquisition, processing, inversion, modeling and interpretation. Complementary to seismic, MT surveys are used for: geologic mapping, in particular mapping sub-basalt structures, foothills, thrust and fold belts; frontier play exploration; reservoir characterization and monitoring; mapping of various base metals, nickel, Cu-porphyry (+/- Au,Mo), VMS, IOCG, kimberlites diamond, graphite; groundwater exploration.
The Induced Polarization (IP) method reliably detects disseminated sulphides which are often associated with economic base metal and gold deposits. This method, along with resistivity, is also used for geological mapping and groundwater studies. CGG uses industry standard equipment to acquire high-quality time-domain IP and resistivity data. Transmitters ranging from portable battery-powered models to high-powered systems are used to ensure the equipment is best suited to the application, the location and to optimize transmitter current and power.
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