In general, inline data are good for detecting thin resistors, whereas broadside data is effective in imaging whether a resistor is thick or thin. However, for anisotropic rocks, inline data are more sensitive to vertical resistivity and broadside are more sensitive to horizontal resistivity. Hence, we use 3D EM with receiver grids in order to acquire both inline and broadside data.
We tow our source over a grid while all the while our receivers lie on the seabed. This allows us to register signals for various azimuth angles while picking up MT signals throughout the survey grid, which are independent of source signals.
As the source is towed, all the surrounding receivers are active, which enables us to record data from all azimuths. Full-azimuth 3D EM data acquisition has major benefits over 2D methods, including:
- Increased data coverage and density
- Improved spatial and depth resolution
- Improved reservoir delineation and greater confidence in small-magnitude anomalies
- Reduced risk of missing small targets
- Datasets suitable for full 3D inversion to enable efficient integration
- Better anisotropy information.