Effects of the airwave in time-domain marine controlled-source electromagnetics

Effects of the airwave in time-domain marine controlled-source electromagnetics

Hunziker, J.W.
Slob, E.C.
Mulder, W.

Civil Engineering and Geosciences

Geoscience & Engineering

2011-06-07

In marine time-domain controlled-source electromagnetics (CSEM), there are two different acquisition methods: with horizontal sources for fast and simple data acquisition or with vertical sources for minimizing the effects of the airwave. Illustrations of the electric field as a function of space and time for various source antenna orientations, based on analytical formulation of the electric field in two half-spaces, provide insights into the properties of the airwave and the nature of diffuse electric fields. Observing the development of the electric field over time and space reveals that diffusive fields exhibit directionality. Therefore, techniques that have thus far mostly been applied to wavefields can be adapted for CSEM. Examples range from the well-known up-down decomposition to beam steering. Vertical sources have the advantage of not creating an airwave. On the other hand, it is quite difficult to achieve perfect verticality of the source antenna. Results, using a numerically modeled data set to analyze the impact of the airwave on a signal from a subsurface reservoir in the case of a slightly dipping vertical source, indicate that already for a dip of 0.05, the airwave contributes 20% to the complete electric field in our configuration of reservoir depth, water thickness, and conductivity values.

antennas
data acquisition
electrical conductivity
geophysical equipment
geophysical prospecting
hydrocarbon reservoirs
rocks
seafloor phenomena

http://resolver.tudelft.nl/uuid:fb992a64-6a35-4c1e-ad5a-bdb5d8efa746

https://doi.org/10.1190/1.3587222

Society of Exploration Geophysicists

0016-8033

Geophysics, 76 (4), 2011

Institutional Repository

journal article

(c) 2011 Society of Exploration Geophysicists