Exploration for Potential Sub-Thrust Prospects in Deep Water Deposits of Mesozoic Age, SE Asia

Overview

This project involved the reprocessing of 3D offshore deepwater seismic data to improve sub-thrust imaging using advanced technologies including Full Waveform Inversion (FWI) and Reverse Time Migration (RTM). Following reprocessing, the study involved mapping multiple seismic horizons beneath a highly disturbed thrust zone, identifying faults of varied tectonic origin, and delineating fault-controlled structural closures. Seismic inversion was performed by integrating seismic data with a single well located approximately 25 km outside the study area. The primary objective was to identify economically viable hydrocarbon prospects.

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The Challenge

Narrow azimuth acquisition led to uneven sampling, footprints, and artefacts. TTI anisotropy estimation was particularly challenging without local well control, requiring reliance on offset data and legacy models.
Maintaining seismic marker continuity and accurately mapping faults below the thrust zone presented a significant interpretive challenge. Predicting reservoir properties through seismic inversion using a dry well situated well outside the block added further uncertainty.
The identified prospects are primarily fault closures, making precise fault delineation critical — both to confirm sufficient displacement for effective sealing, and to identify younger cross faults associated with the thrust system that may act as conduits for hydrocarbon leakage.

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Our Approach

5D interpolation (MWNI) was applied to regularise data and suppress acquisition footprints. Multi-iteration FWI was used to construct a high-resolution TTI velocity model (Vp₀, δ, ε, dip/azimuth), calibrated through well-to-seismic tie using a 2D seismic line from an off-block well. RTM-based TTI PSDM was then performed, with post-migration processing including residual moveout correction, Radon demultiple, and spectral balancing to achieve flattened gathers and enhanced imaging resolution.
Seismic markers corresponding to key geological units were identified and propagated into the 3D volume. Multiple seismic attributes — including amplitude symmetry, sweetness, RTM envelope, relative acoustic impedance, discontinuity, and coherency — were generated across the full 3D dataset, significantly enhancing horizon visibility and continuity beneath the thrust. Fault geometries, both lateral and vertical, were interpreted with high confidence using coherency time slices and supporting attributes.
Refinement of fault geometry and improved horizon interpretation eliminated earlier ambiguities, with previously identified leads reassessed to produce a reduced but more reliable set of drillable prospects. Resource estimation, risking, ranking, and petroleum system analysis were carried out in collaboration with Rose & Associates using their proprietary tools. Seismic inversion across the 3D volume enabled facies distribution mapping and reservoir property estimation, with inversion-derived porosity showing good agreement with porosity trends from subsidence history analysis.

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Results

• Sub-thrust imaging clarity improved significantly, with seismic marker continuity beneath the thrust enhanced through coherency and discontinuity attributes
• Clear identification of fault geometries and improved understanding of relationships between multiple fault sets
• Reinterpretation of horizons and faults removed earlier uncertain leads, shifting the prospect portfolio from broadly defined leads to well-constrained, fault-controlled closures
• Improved ability to distinguish sealing faults from younger cross faults acting as leakage pathways, directly reducing uncertainty in trap integrity and improving chance of success
• More reliable facies distribution and porosity estimation from seismic inversion, despite reliance on a dry well outside the block
• Refined resource estimates from more constrained structural closures and better porosity inputs
• Identification of a limited set of drillable, better-ranked, and economically more viable targets — avoiding investment in ambiguous or high-risk prospects