Open AccessOn the electromagnetic fields produced by marine frequency domain controlled sources
Author(s) -
Chave Alan D.
Publication year - 2009
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2009.04367.x
Subject(s) - geology , magnetotellurics , electromagnetic field , geophysics , electromagnetics , salient , superposition principle , resistive touchscreen , oblique case , physics , computer science , electrical resistivity and conductivity , linguistics , philosophy , engineering physics , quantum mechanics , artificial intelligence , computer vision
SUMMARY In recent years, marine controlled source electromagnetics (CSEM) has found increasing use in hydrocarbon exploration due to its ability to detect thin resistive zones beneath the seafloor. Although it must be recognized that the quantitative interpretation of marine CSEM data over petroleum‐bearing formations will typically require 2‐D surveys and 2‐D or 3‐D modelling, the use of the 1‐D approximation is useful under some circumstances and provides considerable insight into the physics of marine CSEM. It is the purpose of this paper to thoroughly explore the 1‐D solutions for all four fundamental source types—vertical and horizontal, electric and magnetic dipole (VED, HED, VMD and HMD)—using a set of canonical reservoir models that encompass brine to weak to strong hydrocarbon types. The paper introduces the formalism to solve the Maxwell equations for a 1‐D structure in terms of independent and unique toroidal and poloidal magnetic modes that circumscribe the salient diffusion physics. Green's functions for the two modes from which solutions for arbitrary source current distributions can be constructed are derived and used to obtain the electromagnetic (EM) fields produced by finite VED, HED, VMD and HMD sources overlying an arbitrary 1‐D electrical structure. Field behaviour is analysed using the Poynting vector that represents the time‐averaged flow of energy through the structure and a polarization ellipse decomposition of the triaxial seafloor EM field that is a complete field description. The behaviour of the two EM modes using unimodal VED and VMD sources is presented. The paper closes by extending these results to the bimodal HED and HMD sources.