Improving Target Resolution Below Heterogeneous Channels

Advanced velocity model building resolves structural uncertainty and improves the amplitudes affected by complex channel systems.

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The Location

Location

Côte d'Ivoire, Blocks 602 & 603

Survey Year

2015

Data Deliverables

Kirchhoff PSDM, Velocity Model

Survey Type

3D GeoStreamer

Configuration

10 streamers, 100 m separation

Survey Size

5 000 sq. km

TGS data library offers multiple 3D GeoStreamer surveys and over 12 000 line km of 2D data for Côte d'Ivoire. Our border to border MegaSurvey data coverage (gray outline), provides a detailed geological understanding of the region and an excellent overview of all play types over available acreage. The data in this case study is from within the orange outline and was reprocessed in 2018 using advanced velocity model building tools.

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The Challenge

The Challenge

Late Cretaceous (Maastrichtian) and Paleocene channel and canyon systems (yellow ellipses) impact the seismic characterization of older Late Cretaceous prospective channel and fan systems in deepwater Côte d’Ivoire. Intra-channel heterogeneity affects amplitude fidelity and causes uncertainty for the prospective targets in the underlying older channel and fan systems. No wells have been drilled in deepwater Côte d’Ivoire, however with modern regional datasets available, the complex sediment provenance is becoming more understood.

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The Solution

Data

3D GeoStreamer

Processing

Full 3D demultiple

Velocity Model Building

FWI and Q-VMB tomography

Migration

Q-Kirchhoff prestack depth

QI

Seismic driven inversion for relative impedance

An integrated visco-acoustic model building sequence, including FWI and Q-VMB, has been adopted to resolve the impact of complex Late Cretaceous and Paleocene channel systems on deeper targets. This approach eliminates the reflectivity imprint, creates an accurate velocity model, eliminates uncertainty in the image and improves the amplitude-fidelity of the dataset.

Attenuation Effects of Canyons Resolved

Before Image After Image
No Q
With Q
Implementation of fully integrated visco-acoustic model building and migration delivers the results on the right. The removal of the imprint of the canyon on the data below is shown on the log spectra ratio plots (inserts) from the Base Tertiary Unconformity horizon. The spectra on the right demonstrates how the amplitudes have been successfully compensated for below the canyons (blue is ideal).
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The Results

Solving the Challenges of a Complex Set of Deepwater Channel Systems

The primary objective of this model building flow is to solve the seismic characterization challenges of a complex set of deepwater Maastrichtian and Paleocene channel systems on deeper Cenomanian and Turonian fan systems offshore Côte d’Ivoire. Due to water depth (4 km), acquisition geometry and geological setting, reflection only FWI was used as part of a fully integrated visco-acoustic model building flow. In conjunction with FWI, the Q model was derived tomographically. The resulting Q migration produces a seismic image where the younger Late Cretaceous prospectivity is more readily defined, with less uncertainty and improved amplitude fidelity.

Effective Model Building Improves Continuity of Impedance Data

Before Image After Image
Before
After
Relative impedance quality control shows better continuity and resolution of events below the Maastrichtian and Paleocene channels. The interpretation and evaluation of prospective features at target level can be completed with more confidence.