May 17th-Downtown Tech Lunch: Wolfspar, an "FWI-friendly" Ultra-Low-Frequency Marine Seismic Source*
Meeting Location:
Petroleum Club of Houston
1201 Louisiana, 35th
Houston, TX 77004
(Valet parking onsite.)
Meeting Time: 11:00 to 1:00 pm
Registration Begins at 11:00
Lunch Served at 11:30
Presentation starts at Noon
NOTE: You Must Be Logged In to Register.
Speaker: Joe Dellinger, BP America
Co-Authors: Allan Ross, David Meaux, Andrew Brenders, Glenn Gesoff, John T. Etgen, and John Naranjo, BP America
Graham Openshaw, TecPM and Mark Harper, Cambridge Applied Physics
Over
the past decade, BP designed, built, and field tested Wolfspar®, a
full-scale, ultra-low-frequency seismic source capable of producing
frequencies of 1.4 – 8 Hz. This was quite an ambitious project to
undertake, and was the culmination of years of thinking differently
about the challenge of seismic imaging in deep water under complex salt.
First, we realized that our wide-azimuth seismic data have
become good enough that they are no longer the primary impediment to
imaging under complex salt. The limiting factor is now our velocity
models. Our “Garden Banks” model study showed that in areas of complex
salt, our velocity models likely include “interpretation busts”, where
cubic kilometers of the velocity model may have salt where there should
be sediment, or vice versa. These mistakes are very hard to identify and
fix using any form of manual interpretation --- if that strategy
worked, the problem would have been solved by now. Model studies showed
that FWI can fix these problems, but requires seismic data with
ultra-low frequencies (below 2 Hz) recorded at wide offsets (20-30 km)
to do so. The problem then becomes, how can we get the required data at a
reasonable cost? How do we design an entirely new acquisition strategy
around velocity-model-building using FWI?
Acquiring frequencies
below 2 Hz at wide offsets introduces a whole new set of challenges.
Marine seismic sources naturally roll off at low frequencies at about 18
dB / Octave, and below 2 Hz the natural microseismic background noise
also rapidly increases, resulting in a very steep S/N “wall” to climb.
It is very difficult to penetrate this noise wall. We need a source that
increases the signal at low frequencies that does not also create
undesirable additional high frequencies. Conventional broadband sources
are not well suited to the challenge. These considerations drove us to
controlled sources that could tailor their output to concentrate their
power on just the required frequency range. Conventional marine vibrator
designs optimized to produce 10-100 Hz are problematic to scale up to
produce lower frequencies, however. To maintain a constant far-field
amplitude, the volume of water to displace scales as inverse frequency
cubed, so a 1 Hz source would need to displace 1000 times the volume of a
10 Hz source of the same design. The power required to move such a
large volume of water using vibrator technologies can become
impractically large. Our solution was an energy-efficient, resonating
piston design. The engineering challenge of how to seal a 1.6-meter
diameter piston moving back and forth over a range of motion of half a
meter proved to be solvable. Field-testing the source under tow at 4
knots, recording into ocean-bottom sensors, we achieved an excellent
signal-to-noise ratio in the deep water Gulf of Mexico at offsets of
over 30 km and at frequencies as low as 1.6 Hz despite the significant
ambient noise at these frequencies.
Now that a prototype source
exists, the remaining problem is acquisition design. Streamers are noisy
at low frequencies and don’t easily accommodate the necessary offsets
and azimuths. This drives us to a low-noise nodal acquisition.
Conventional node arrays spaced ~400 meters apart recording offsets out
to 30 km or more at all azimuths would be quite expensive. The key is to
realize that we are designing the survey to record low-frequencies for
velocity-model-building, not for conventional imaging purposes. Sampling
considerations allow us to consider a cost-efficient sparse 3D
acquisition geometry, reminiscent of land acquisition strategies of the
late 1990’s, but performed at sea. We believe that by rethinking
acquisition from end to end, we can meet the challenge of imaging in
areas of deep water and complex salt.
Speaker Biography: Joe Dellinger, BP America
Joe Dellinger received a PhD in 1991 from Jon Claerbout’s Stanford Exploration Project, then did a 3-year post-doc at the University of Hawai`i before joining Amoco’s Tulsa Research Center in 1994. He moved to BP in Houston in 1999 and has worked there since. In his career he has specialized in Anisotropy, multi-component algorithms and processing, and most recently rethinking marine seismic acquisition. As part of that work he has spent considerable time closely examining seismic data trying to understand all the signals present in it. He calls this “Forensic data processing”, which was the title and subject of his 2016 Spring SEG distinguished lecture series (41 talks in 11 countries in 3 months!). Since 2006 Joe has been the lead BP geophysicist supporting BP’s “Wolfspar” project, with the goal to design, build, deploy and commercialize an ultra-low-frequency marine seismic source.
Joe was awarded SEG life membership in 2001 and honorary membership in 2016 for his services in helping the SEG to adapt to the internet age. Joe’s hobbies include attending the Houston Symphony, photographing birds, recording frog calls in the swamps around Houston, and public outreach astronomy at the George Observatory. Asteroid “78392 Dellinger” was named in his honor.
Price List:
|
Pre-Registered |
Late/Walk-Up
|
Member
|
$35 |
$45 |
| Non-Member |
$45 |
$55 |
Student Member
|
$0 |
$10 |