Hunting for microseismic reflections using multiplets

Introduction

Hydraulic fracturing is routinely used to increase production rates from unconventional resources such as tight sands and shale plays. Its effectiveness depends largely on the geometry of the induced fractures. Microseismic monitoring is often used to assess this geometry by picking these earthquake-like arrivals and locating their sources along the fractures.

Microseismic recordings also contain reflected arrivals that may be useful for imaging the reservoir (Tamakawa et al., 2010; Asanuma et al., 2011; Reshetnikov et al., 2009). However, due to their small magnitudes, such reflections may not be easy to identify on a seismogram. In this work we key on the frequent presence of repeated events known as multiplets that originate from about the same subsurface location and have nearly identical source characteristics. Our assumption is that they must also generate nearly identical reflections. By extracting, aligning and stacking these events we reduce background noise and enhance both the direct arrivals and the weaker reflections that follow them.

Our aim for reflection identification is to use these high frequency deep sources to image the subsurface. Although such a use of microseismic sources has been done before in subsurface imaging (Tamakawa et al., 2010; Asanuma et al., 2011; Reshetnikov et al., 2009), to the best of our knowledge none of these sources were hydraulically induced.

Hunting for microseismic reflections using multiplets