The Drill Bit Seismic Project at SAFOD

In July 2002, scientists from Duke University successfully installed a downhole seismic array at the SAFOD site in collaboration with SAFOD Principal Investigators Bill Ellsworth (USGS), Steve Hickman (USGS), and Mark Zoback (Stanford University). As part of ongoing seismic studies at SAFOD, the vertical array of three component seismometers is currently being used in a drill bit seismic experiment in conjunction with two surface geophone arrays donated by Schlumberger, Inc.

The purpose of this experiment is to collect an inverse vertical seismic profile from signals generated by the drill bit while drilling the SAFOD borehole. These signals are being simultaneously recorded by the three geophone arrays and accelerometers installed on the top drive of the drill rig. The drill bit itself acts as a downhole seismic source capable of illuminating its surrounding. The energy generated by the drill bit is then recorded by the geophone arrays. This type of data collection has been referred to as the "drill bit seismic method". The goal of the joint project between Duke University and Schlumberger is to make use of the borehole drilling operation itself as a source of seismic energy for imaging the complex subsurface geologic structure of the San Andreas Fault while the drilling progresses. An additional goal of the experiment is to record fault zone guided waves at the location of the Buzzard Canyon fault and other unmapped faults between the drilling rig and the San Andreas Fault. In this paper, we present an overview of the DBSeis processing architecture, initial results of our experiment, and preliminary subsurface images of the SAFOD site.