Unlocking Prospectivity on the Kwanza Shelf​

Home Case Studies Unlocking Prospectivity on the Kwanza Shelf​

3D GeoStreamer acquisition combined with advanced processing techniques unveil key elements for a successful petroleum system in both the pre- and postsalt sections on the Kwanza Shelf

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The Location

Location

Kwanza Shelf, Angola

Survey Year

2019 and 2020

Survey Type

3D GeoStreamer

Streamer Configuration

12 streamers x 112.5 m x 8 025 m

Source Configuration

Triple

Survey Size

8 304 sq. km

In partnership with Agência Nacional de Petróleo, Gás e Biocombustíveis (ANPG), TGS has acquired a multisensor GeoStreamer survey over the Kwanza Shelf (orange polygon). This data provides enhanced subsurface illumination through broadband acquisition and the use of modern processing workflows tailored to the unique imaging challenges of shallow water and salt presence. This broadband 3D multiclient dataset will equip explorers with the tools to identify and unlock the pre- and post-salt plays in this underexplored area of the Angolan offshore.​

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The Challenge

Historical Absence of Data Presents Challenges

The historical absence of high-quality seismic data over the Kwanza Shelf has presented a significant challenge to recent hydrocarbon exploration efforts. With proven plays encountered in the syn-rift, sag phase, and post-rift sections, clearer imaging of presalt stratigraphy and structure is needed to unlock prospectivity. Complex geometries associated with the overlying Loeme Salt Formation require detailed velocity model building to create an accurate presalt image.​

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The Solution

Data

Broadband 3D GeoStreamer

Ultra Efficient

Single vessel, wide-tow sources, dense spreads, long tails

Well Data

rockAVO

Processing

Deblending, full 3D demultiple and 4D regularization​

Velocity Model Building

Reflection and refraction tomography, FWI and RTM for salt model building

Imaging

Kirchhoff, RTM and SWIM

Q modeling

Variable Q model using tomographic and scanning method​

A combination of reflection and refraction tomography has been used in conjunction with FWI to generate a detailed velocity model which gives enhanced imaging of complex salt bodies and presalt reflections. A variety of migration algorithms including SWIM, RTM and KPSDM have been utilized to produce multiple volumes which contribute to improved interpretation in a geologically complex region.​

SWIM Delivers High Resolution Shallow Imaging

Before Image After Image
KPSDM
KPSDM & SWIM
Final KPSDM full-stack versus the merged final SWIM & KPSDM full-stack. Merging the SWIM and the final KPSDM volume utilizes the best of both imaging algorithms. SWIM improves the near-surface image leading to greater resolution of the near-surface geology by resolving shallow channels and removing the acquisition footprint.​

Salt and Presalt Better Imaged with RTM ​

Before Image After Image
KPSDM
RTM
Final KPSDM full-stack volume versus the final RTM stack (migrated to a maximum frequency of 40 Hz). The RTM gives greater continuity along the top and base salt reflectors (blue arrows). The presalt also shows an uplift in imaging, particularly where the salt structures above are more complex (yellow arrows).​
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The Results

High-quality 3D data allows for detailed mapping

Tertiary sandstones deposited in turbidite channel systems offer excellent potential reservoirs (26-30% porosity and >400md permeabilities) and are analogous to those established in the prolific Lower Congo Basin. High-quality 3D data allows for detailed mapping of extensive stacked channel networks with additional reservoir potential also occurring in postsalt Albian carbonates. Quantitative Interpretation has identified AVO anomalies associated with hydrocarbon presence in these deposits. Hydrocarbons generated from source rocks in the presalt section have the potential to migrate into the post-rift via salt welds. Reservoirs can also be charged from postsalt sources through faults created by halokenisis, or by simple up-dip migration through carrier beds.

QI Reveals a Working Petroleum System

Before Image After Image
KPSDM
P Impedance
The salt, highlighted in pink, has welded out and post-rift mini basin touch-down has occurred onto the top of the sag phase presenting a potential migration route for hydrocarbons (orange arrow). Faulting, shown in black, can be observed to act as a conduit for hydrocarbons to migrate from the presalt, into the postsalt. P-Impedance anomalies can be seen in the post-rift suggesting that there is potential for these fluids to be trapped in high-quality Tertiary sandstones and postsalt Albian carbonate reservoirs.​
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