Magnitude vs low frequency EM waves for sea bed logging applications

Abstract

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.