Extraction of unconventional gas involves the movement of fluids at depth.
In the case of shale gas, hydraulic fracturing is performed, where fluids are
injected into sequences at high pressures resulting in permeable pathways
for the trapped gas to escape. Coal seam gas (CSG) extraction involves
a process termed depressurisation, where large volumes of groundwater
are extracted from coal measures causing a pressure reduction that allows
trapped gas to desorb from the coal seams. One of the key questions the
industry sector is facing is whether it can effectively monitor movement
of fluids and changes in Earth as these unconventional energy resources
are being developed. We present two MT monitoring surveys of unconventional
energy resource development. The first survey involves an industrial
field study conducted in Queensland, Australia, where MT responses indicated
the orientation of fluid flow resulting from depressurisation, which
can be mapped and directly attributed to spatial and temporal variations
in permeability. The second survey involves monitoring deep hydraulic
fracturing of a shale gas reservoir in the Cooper Basin, Australia. MT observations
indicated increases in bulk conductivity of 20 – 40% in both the
temporal and spatial domain, with these changes caused by a combination
of both injected fluid permeability and an increase in wider-scale in-situ
permeability. Finally the telluric sounding method is introduced as a potential
tool for monitoring hydraulic fracturing at depth. The advantage
of this method is that it is relatively easy to measure electric fields with
many dipoles and multi-channel systems and therefore electric field arrays could be deployed and left out for continuous monitoring. Additionally,
electric field transfer functions are essentially the identity matrix for a 1D
Earth no matter what the vertical structure is and therefore monitoring
involves plotting deviations relative to the identity matrix.Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Physical Sciences, 2016
