Fernandes, Roland Anthony Savio (2008-05). The effects of cultural noise on controlled source electromagnetic resonses of subsurface fractures in resistive terrain. Master's Thesis. Thesis uri icon


  • Controlled source electromagnetic (CSEM) geophysics has been used with a fair
    amount of success in near surface hydrogeological studies. Recently, these investigations
    have been conducted frequently in human impacted field sites containing cultural
    conductors such as metal fences and buried pipes. Cultural noise adds an element of
    complexity to the geological interpretation of this type of data. This research investigates
    the influence of mutual induction between two buried targets in a CSEM experiment. In
    particular, it looks at the mutual coupling between a buried cultural conductor and a
    geological heterogeneity. We attempt to isolate the Hz field induced by tertiary currents
    in targets caused by mutual coupling. This is achieved with a Texas A&M 3D CSEM
    finite element code, which calculates the secondary Hz fields emanating from a target
    buried in a halfspace. Buried geological targets and cultural conductors are modeled as
    volumetric slabs embedded in a halfspace. A series of models have been simulated to
    study the effect of varying parameters such as target conductivity, transmitter location
    and shape of a target on the mutual inductance. In each case, the secondary Hz field is
    calculated for a model with two slabs, and two models with individual slabs. The mutual
    coupling is calculated by removing the secondary fields from the individual slab models
    from the response of a two slab model. The calculations of mutual inductance from a
    variety of such models suggests a complicated interaction of EM fields between the two
    targets. However, we can explain most of these complexities by adapting a simple
    approach to Maxwell's equations. Although the tertiary Hz field is complicated, it may be useful in the
    characterization and delineation of electrical heterogeneities in the subsurface, which can
    then be related to geological features such as fractures or joints. It is seen that the most
    important factor affecting the mutual coupling is the host conductivity. The results have
    also shown that mutual coupling is very sensitive to transmitter (TX) location, especially
    when the TX is positioned near one of the targets.

publication date

  • May 2008