Reservoir imaging under complex overburden and virtual-source imaging

Technologies have been developed over the years to understand how fluid flows through reservoirs during production. However, where karst or near-surface basalt conditions occur, it becomes impossible to image the reservoirs due to excessive seismic scattering. A new method has been developed and patented, in which a low cost horizontal well is drilled beneath the overburden, to allow the insertion of a seismic cable and consequent recording of seismic data, to produce an image of the reservoir for the first time. An initial experiment will be performed over methane coal fields in Queensland in an attempt to demonstrate this as a feasible solution to imaging reservoirs beneath complex karst and basalt topography.

For this purpose a low cost low power continuous vibratory system has been developed for seismic imaging applications over reservoirs. In addition, methods of time reversed acoustics have been successfully applied to imaging targets beneath strongly scattering near-surface layering. The use of continuous sources holds promise of considerably improving the precision of seismic measurements. Changes in travel time of less than a micro-second can be achieved and will lead to measurements of frequency dependent velocity measurements of fluids in porous media. Changes in the velocity dependent dispersion will lead to the characterisation of fluids and of reservoir conditions as fluids are injected or withdrawn from reservoirs.

This has developed now to laboratory and numerical simulation of the application of time reversed acoustics in simulating sources below surface multi-scattering layers in a method known in geophysics as the Virtual Source Method.