HR: 1340h
AN: T13A-1346    [Abstracts]
TI: High-Resolution Fault Zone Monitoring and Imaging Using Long Borehole Arrays
AU: * Paulsson, B N
EM: bjorn.paulsson@paulsson.com
AF: Paulsson Geophysical Services Inc., 1215 W Lambert Rd., Brea, CA 92821
AU: Karrenbach, M
EM: martin.karrenbach@paulsson.com
AF: Paulsson Geophysical Services Inc., 1215 W Lambert Rd., Brea, CA 92821
AU: Goertz, A V
EM: alex.goertz@paulsson.com
AF: Paulsson Geophysical Services Inc., 1215 W Lambert Rd., Brea, CA 92821
AU: Milligan, P
EM: paul.milligan@paulsson.com
AF: Paulsson Geophysical Services Inc., 1215 W Lambert Rd., Brea, CA 92821
AB: Long borehole seismic receiver arrays are increasingly used in the petroleum industry as a tool for high--resolution seismic reservoir characterization. Placing receivers in a borehole avoids the distortion of reflected seismic waves by the near-surface weathering layer which leads to greatly improved vector fidelity and a much higher frequency content of 3-component recordings. In addition, a borehole offers a favorable geometry to image near-vertically dipping or overturned structure such as, e.g., salt flanks or faults. When used for passive seismic monitoring, long borehole receiver arrays help reducing depth uncertainties of event locations. We investigate the use of long borehole seismic arrays for high-resolution fault zone characterization in the vicinity of the San Andreas Fault Observatory at Depth (SAFOD). We present modeling scenarios to show how an image of the vertically dipping fault zone down to the penetration point of the SAFOD well can be obtained by recording surface sources in a long array within the deviated main hole. We assess the ability to invert fault zone reflections for rock physical parameters by means of amplitude versus offset or angle (AVO/AVA) analyzes. The quality of AVO/AVA studies depends on the ability to illuminate the fault zone over a wide range of incidence angles. We show how the length of the receiver array and the receiver spacing within the borehole influence the size of the volume over which reliable AVO/AVA information could be obtained. By means of AVO/AVA studies one can deduce hydraulic properties of the fault zone such as the type of fluids that might be present, the porosity, and the fluid saturation. Images of the fault zone obtained from a favorable geometry with a sufficient illumination will enable us to map fault zone properties in the surrounding of the main hole penetration point. One of the targets of SAFOD is to drill into an active rupture patch of an earthquake cluster. The question of whether or not this goal has indeed been achieved at the time the fault zone is penetrated can only be answered if the rock properties found at the penetration point can be compared to the surrounding volume. This task will require mapping of rock properties inverted from AVO/AVA analyzes of fault zone reflections. We will also show real data examples of a test deployment of a 4000 ft, 80-level clamped 3-component receiver array in the SAFOD main hole in 2004.
UR: http://www.paulsson.com
DE: 7260 Theory and modeling
DE: 7294 Instruments and techniques
DE: 8010 Fractures and faults
DE: 7200 SEISMOLOGY
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting