Observations and implications from simultaneous recording of microseismic surface and borehole data

Abstract

Simultaneously recording microseismic surface and borehole data (hereinafter referred to as co-recorded data) offers some unique challenges. In many cases, timing differences between the surface and borehole data sets cannot be accurately resolved, which greatly limits the usefulness of the experiment. Velocity models that are derived from sonic well logs and calibrated for each seismic data type are typically incompatible, and cannot be used for simultaneous focusing of the events. However, despite the acquisition and processing challenges, co-recorded surface and borehole data also offer some unique benefits. The inherent sensitivity of borehole data allows us to routinely determine when the reported events from the processed surface data include “false positives” (reported events that actually do not exist), and provides an opportunity to improve our surface data-processing algorithms and workflows to reduce false positives. The inherent horizontal accuracy of surface data allows us to determine when the event azimuths from borehole data are inaccurate, and provides an opportunity to improve the accuracy of our borehole data-processing algorithms. The difficulty in resolving the velocities is actually a benefit, because it allows us to constrain the velocities, and constrain anisotropy, to produce more accurate location results. Simultaneous recording of surface and borehole data may offer some of the benefits of using multiple observation wells.