Improving microseismic imaging: Role of acquisition, velocity model, and imaging condition

Surface microseismic data is being increasingly used in monitoring hydraulic-fracturing. Here, we suggest changes in the acquisition as well as processing stages to improve microseismic imaging and source characterization. Improved microseismic hypocenter imaging and reliable source mechanism estimation can be achieved by illuminating the hypocenter evenly from all directions. We introduce methodologies for designing optimized surface arrays for 2D and 3D acquisitions. Accurate microseismic imaging also requires the exact Green's function between the image point and the receivers. An inaccurate Green's function leads to poor focusing and numerous spurious microseismic hypocenters. We also introduce imaging conditions that can yield accurate source signatures even if they are extended in space and time. Such source signatures can yield the time history of fracture propagation in space and might be used to infer the time-varying slip along pre-existing fractures. These imaging conditions also reduce spurious events in the image. All conclusions are supported with numerical examples.