Vertical slowness constrained joint anisotropic parameters and event locations inversion for downhole microseismic monitoring

The construction of accurate anisotropic velocity models plays a very important role in microseismic monitoring of hydraulic fracturing. Due to ignorance of anisotropy, severe distortions may happen in the results of microseismic location and interpretation. While the methods are existing that invert for anisotropic parameters and event locations simultaneously with microseismic traveltime, the results hinge on good velocity models and enough ray coverage for multiple parameters. Meanwhile, microseismic waveform inversion for anisotropic parameters is still challenging because of low signal-noise ratio (SNR) of...  more

The construction of accurate anisotropic velocity models plays a very important role in microseismic monitoring of hydraulic fracturing. Due to ignorance of anisotropy, severe distortions may happen in the results of microseismic location and interpretation. While the methods are existing that invert for anisotropic parameters and event locations simultaneously with microseismic traveltime, the results hinge on good velocity models and enough ray coverage for multiple parameters. Meanwhile, microseismic waveform inversion for anisotropic parameters is still challenging because of low signal-noise ratio (SNR) of the data and high computation cost. Based on the assumption of small horizontal velocity variation, we develop a method jointly inverting event locations and velocity updates using traveltimes and vertical slowness estimates. The vertical slowness estimates are independent of the source information and easy to be obtained.We apply the developed method into four synthetic examples under different circumstances. The results demonstrate that the vertical slowness can effectively constain and stabilize the conventional traveltime inversion method, in particular for the cases with the poor raypath coverage. We further employ this method for one field case where the event locations are more reasonable comparable to the inversion with traveltimes only.