Outer Vøring Norwegian Sea

Solving Imaging Challenges in a Deepwater Complex Ooze Regime

Outer Vøring Area, Norwegian Sea

Derisk by resolving complexities and creating accurate velocity models and reliable images

Locations

Location
Outer Vøring, Norwegian sea
Survey year
2016
Survey type
3D GeoStreamer
Survey configuration
16 streamers, 75 m separation, 8100 m length
Area
5 500 sq. km
Water depth
800 - 1 600 m
Streamer tow depth
25 m
Locations

This project (orange outline) was the first commercial survey acquired by Ramform Tethys deploying 129 km of in-sea recording cable. Two years later, this is still the biggest spread towed by a seismic vessel in Northern Europe. Globally, this achievement has only been matched by Ramform Tethys' sister vessels in the Ramform Titan-class fleet. Visit our data library for more information on data availability.

The Challenge

Reservoir targets in the area sit deeper than complex ooze bodies. In order to accurately image the targets the ooze bodies must be effectively resolved. Deep water and lack of refractions from strong negative velocity contrasts at the top of the ooze bodies mean that traditional FWI is not optimal. The ooze also causes strong scattering of the wavefield and results in distortions and amplitude diming effects which must also be addressed.

PGS16004 3D GeoStreamer data

Solution

Data
Good S/N due to multi-sensors and deep tow
Processing
4 ms
Signal processing
Full 3D demultiple
Velocity model building
PGS FWI using reflections and refractions
Frequency range for FWI
2-12 Hz
Q modeling
Variable Q model to capture high-absorption ooze bodies
Migration
Q-Kirchhoff pre-stack depth
Solution

The PGS FWI solution includes reflections and refractions to provide deeper and higher resolution velocity models. Small-scale velocity variations and sharp velocity contrasts between the ooze bodies and surrounding lithology are captured. Q modeling is included to compensate for amplitude distortions and to ensure absorption is incorporated during the migration.

Ooze Bodies Better Resolved
with PGS FWI

Initial Initial
Initial 12 Hz FWI

PSDM stack and 1 700 m depth slice for the initial (left) and final FWI velocity model overlays (right). Ooze bodies are much better resolved with reflections and refractions in PGS FWI.

Results

High-resolution velocity models down to depths of 4 km have been generated due to the availability of FWI frequencies down to 2 Hz and the inclusion of reflections in the calculations. Targets beneath the ooze are better imaged as the high-resolution velocity models have been combined with detailed attenuation (Q) models in a Q-Kirchhoff pre-stack depth migration.

Increasing FWI Frequency to 27 Hz For Superior Delineation of Shallow and Deep Ooze Bodies

12 Hz FWI 12 Hz FWI
12 Hz FWI 27 Hz FWI

12 and 27 Hz velocity model overlays on a 1530 m Q-KPSDM section. Note the resolution of localized ooze features in the 27 Hz FWI velocity model.

27 Hz FWI + Q-WEM for an Accurate Image
Corrected for Velocity Variations Due to Ooze

Q-KPSDM Q-KPSDM
Q-KPSDM Q-WEM

Q-KPSDM run with a 12 Hz FWI velocity model versus Q-WEM run with a 27 Hz FWI velocity model and masked shallow Q model.  Note the Q-WEM image is significantly less distorted below the thick ooze body. The resolution of faults and geological contacts and facies boundaries is improved.

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Sören Naumann

Sören Naumann

Imaging Specialist

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Erik Ewig

Vice President, Sales Europe

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Grunde Rønholt

Grunde Rønholt

Manager, Imaging Europe

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