Microseismic Event Estimation via Full Waveform Inversion

Wednesday, May 13, 2015 - 9:00am - 9:50am
Keller 3-180
Susan Minkoff (University of Texas at Dallas)
Hydraulic fracturing is used to enable extraction of oil and gas from low permeability materials such as shale. A high pressure liquid is injected into the well to induce fractures that will allow fluids to flow more freely. The buildup of energy due to increased pressure in the rock leads to stress changes which may ultimately induce small earthquakes or microseismic events. These microseismic events can in turn be used as passive sources for improved imaging of the subsurface. However, in order for a microseismic event to be useful for imaging, its description must be known. As a result, determining microseismic source parameters, such as location and onset time, has become an important area of research in exploration seismology. Full waveform inversion accurately estimates the spatial and temporal components of a microseismic source. Assuming two-dimensional acoustic wave propagation, the gradient is computed via the adjoint state method for both the space and time components of the source waveform. Neither of these gradients requires storing the forward solution of the wave equation as is required by the imaging condition for
velocity inversion. Advantages of the method include the ability to handle extremely low signal-to-noise ratios, the ability to identify multiple sources, and the ability to produce accurate results in the absence of a good initial estimate for the source.