Elastic microseismic full waveform inversion: synthetic and real data

Nadine Igonin and Kris Innanen

ABSTRACT

In the microseismic and seismology field, determining the hypocenter of seismic events is necessary, and requires an accurate velocity model. In conventional FWI, one of the outputs is often a P- and/or S-wave velocity model obtained from (in most cases) sources on the surface. It is not difficult to imagine a framework where microseismic events could be used as additional subsurface sources that could increase the illumination in the reservoir. Furthermore, the velocity model obtained from such a scheme would be useful to re-locate said microseismic events more accurately. Therefore, this symbiotic relationship can be taken advantage of to formulate a FWI implementation where microseismic events are used to simultaneously update the velocity model, and the source position. This would involve two updates at each iteration - one for the velocity model and one for the source position. In this report, we explore in detail the source-term gradient in an elastic 2D formulation. We discuss the effect of the starting position, dominant frequency, moment tensor, and receiver geometry. Furthermore, we explore the impact of cross-talk due to having an incorrect starting velocity model. Finally, we end with preliminary results with a real dataset from the Horn River Basin, British Columbia.

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