Magnitude vs Low Frequency EM Waves for Sea Bed Logging Applications

The new emerging technique for finding
resistive layers in the subsurface which can be
hydrocarbon-saturated reservoirs using Marine controlled
source electromagnetic (CSEM) is called seabed logging
(SBL). It uses a mobile horizontal electric dipole (HED)
source which generates ultra low frequency (0.1 – 10 Hz)
but powerful electromagnetic signal while being towed at
about 30 – 40m above an array of seafloor electric field
receivers. These arrays of receivers will receive signal in
the form of direct waves, air waves, reflected waves and
refracted waves and is measured in the form of amplitude
and phase. The amplitude and phase of this signal depend
on the resistivity of the mediums that they travel.
Hydrocarbon is known to have high resistivity value of 30 -
500Ωm, in contrast to conductive sea water of 0.5 - 2 Ωm
and sediments of 1 - 2Ωm. This paper will investigate and
discuss the effect of these receivers readings in term of
direct waves, air waves, reflected waves and guided waves
as we increased the frequency value from 0.01Hz to 10Hz.
Using simulator that has been developed using MATLAB
software we will set up a forward model that contains air,
sea water, sediments and hydrocarbon reservoir with their
predefined resistivity values. From here we shall discuss
the trend on wave amplitude obtained at different
frequency values.
Keywords- Seabed Logging, Electromagnetic Waves, Airwaves