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Borehole Acoustic Imaging using 3D STC and Ray Tracing to Determine Far-Field Reflector Dip and Azimuth

Speaker: Nicholas Bennett (Schlumberger-Doll Research)
Date: Wednesday, Nov 7th 2018
Venue: MetaRock Laboratories: 2703 Highway 6 S, Suite 280A, Houston, TX 77082
Time: 11:30 am – 01:00 pm
Admission: Regular Admission ($15)
Student and In Transition Professionals ($10)
Parking Info: Parking lot located in front of the building.
Please register by Nov 6th 2018 @ 12 pm to reserve lunch and pre-registration
Contact: Jeff Crawford
Corresponding: // 281-871-2168
While sonic imaging can provide higher resolution images of the near wellbore region than lower frequency seismic and VSP measurements, many challenges confront its more widespread use. The traditional sonic imaging workflow of first filtering the borehole modes and then migrating the underlying reflected arrival events ignores a critical interpretation step, namely characterizing these reflected arrivals in terms of their azimuths, raypath types, and other attributes. Furthermore, using sonic imaging results in subsequent modeling and simulation workflows requires determining the 3D coordinates or at least the true dip and azimuth of these near wellbore reflectors, and feature extraction from noisy 2D sonic imaging migration images cannot provide either of these.
To address these interpretation challenges and develop a means of mapping these reflectors without requiring a migration, a central issue that arises is whether we can determine the slowness and propagation direction of a reflected wavefield using a standard array of receiver sensors mounted around the circumference of a tool sonde. To accomplish this task, we introduce the 3D slowness time coherence as a variation of the more well-known slowness time coherence processing of Kimball and Marzetta, demonstrate the technique on simulated and field measurements, and provide estimates of the precision with which slowness can be determined in directions orthogonal to the tool sonde.
We combine use of this 3D slowness time processing with a ray tracing inversion to study a manually picked arrival event selected from field measurements. We determine its raypath type and azimuth and then map the corresponding reflector relative to the well track.  To formulate a more practical workflow usable in wireline logging scenarios, we demonstrate how to combine this ray tracing and 3D STC coherence processing with an automated time pick procedure to evaluate the many candidate arrival events which may be present in the filtered waveform measurements. This combined workflow generates both a 3D map of the reflectors that can be readily integrated into digital models of the surrounding subsurface as well as logs of reflector true dip and azimuth that can be compared with similar logs produced from borehole images.
Nicholas Bennett is currently a Principal Research Scientist at Schlumberger-Doll Research Center, Cambridge, Massachusetts where he has been working since completing his Ph.D. in Mathematics from Yale University in 1997. Nick’s main activities involve acoustics, nuclear magnetic resonance, and electromagnetic measurements.
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