4D Geophysical Imaging of Subsurface Resources


The market potential for sophisticated 3D/4D Electromagnetic ("EM") geophysical imaging of sub-surface resources is already substantial and the need for more sophisticated data acquisition is growing rapidly. Australia has identified resources of more than 150 trillion cubic feet of Coal Seam Gas (CSG), almost 400 trillion cubic feet of Shale Gas and 20 trillion cubic feet of Tight Gas.


EM methods utilise either natural-source field variations or a transmitter of EM signals to determine the distribution of electrical resistivity in the earth.  By examining the frequency-dependent response of the earth to time-varying inducing fields, it is possible to determine the resistivity in three-dimensions (3D), and on scale-lengths of a few tens of metres to kilometres.


Induced change in the earth, in the form of fluids (electrically conductive) injected into a reservoir at depth, can produce a measurable change in the EM response, collected at the surface.  Such measurements can be used to estimate the direction and distance that sub-surface fluids are penetrating natural fracture networks and hence indicate the degree of permeability in the host mineral.  Thus, EM represents one of the few methods to actually determine connectivity of fluid flow (at depth) without the need for drilling additional boreholes.


One of the primary drivers of the value of an exploration asset is its geological prospectivity. The prospectivity of an exploration asset is typically assessed through the interpretation of a range of geological, geochemical and geophysical data by subject matter experts. In addition, assessment of the profitability when weighed against the costs is fundamental to valuing a target resource, also taking into account the environmental impacts of exploration, both of which are subject to a high degree of uncertainty.


For the resource and energy sectors, there is great importance in understanding sub-surface variations that affect the movement of fluids.

Patent Information:
For Information, Contact:
Kiara Bechta-Metti
The University of Adelaide
Graham Heinson