Assessing subsurface seismic velocity anisotropy for hydrocarbon reservoir characterization using joint refraction and reflection tomography in a faulted basin

Project Abstract

This study presents a comprehensive investigation into subsurface seismic velocity anisotropy as a key parameter for hydrocarbon reservoir characterization, employing an integrated joint refraction and reflection tomography framework within a tectonically complex faulted basin. By combining refraction-seismic constraints with multi-azimuth reflection data, the research aims to quantify directional dependence of P- and S-wave velocities and relate anisotropy to fracture density, stress regime, and lithological contrasts. The methodology advances conventional isotropic tomography by incorporating anisotropic parameterization using a transversely isotropic TI with a vertical symmetry axis appropriate for layered faulted settings, enabling more accurate delineation of fracture networks and fluid-filled zones. A novel data fusion scheme merges wide-aperture refraction data, high-resolution surface-source gathers, and depth-m migrated 3D reflection volumes to recover both intrinsic velocity and orientation of the anisotropy ellipsoid (folding angle and symmetry axis). The study leverages synthetic modeling to test the sensitivity of travel-time and waveform attributes to azimuthal velocity variations, followed by a rigorous inversion framework that alternates between anisotropic velocity updates and ray/path corrections to mitigate nonlinearity and trade-offs with isotropic components. Field data are acquired across a faulted basin with known hydrocarbon accumulations, involving calibrations from check-shot, vertical seismic profiling, and well-log anisotropy measurements to constrain the anisotropic model parameterization and to validate reservoir-scale interpretations. We develop a robust workflow for preprocessing, including robust source wavelet estimation, anisotropic moveout corrections, and azimuthally diverse sampling to minimize leakage between isotropic and anisotropic signals. The inversion utilizes a hierarchical scheme first recovering TI parameters at coarse scale to capture large-scale fracture fabrics, then refining with higher-resolution updates constrained by borehole logs and geological priors. The research interrogates the relationship between seismic anisotropy and fracture closure, poroelastic effects, and permeability anisotropy, linking velocity ellipses to fracture orientation, density, and fluid saturation. The expected outcomes include improved reservoir delineation, facies discrimination, and more reliable pitch-and-yend interpretations of fracture networks, ultimately enhancing hydrocarbon detection and recovery strategies in complex faulted basins. The study also assesses uncertainty through stochastic perturbation analyses and ensemble tomography, providing probabilistic risk assessments for reservoir targeting. By integrating anisotropic tomography with data-driven geological modeling, the work intends to deliver a scalable workflow that can be adapted to other tectonically complex basins, advancing both methodology and practical reservoir characterization. The final results will include anisotropic velocity models, fracture orientation maps, and validated petrophysical correlations, accompanied by guidelines for incorporating anisotropy into routine seismic interpretation and reservoir simulations.

Project Overview

What This Project Is About

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A straightforward, non-technical overview of how scientists study the underground to locate hydrocarbons. The project looks at how rocks can transmit seismic waves differently depending on their internal structure, and how combining two methods (refraction and reflection) helps map those differences more clearly in areas with faults.

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The Problem It Addresses

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Hydrocarbon reservoirs can be hard to identify when rocks are fractured or tilted by faults. Traditional methods might miss important directions of rock properties, leading to incomplete or uncertain results. This project tackles the challenge of measuring and interpreting how seismic velocity varies with direction (anisotropy) to improve reservoir maps.

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Objectives of the Project

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1. Explain what seismic velocity anisotropy is in simple terms.
2. Show how refraction and reflection data can be combined to detect anisotropy.
3. Demonstrate a basic workflow for processing seismic data in a faulted setting.
4. Interpret what anisotropy tells us about rock properties and possible fluids.
5. Discuss limitations and uncertainties in measurements.

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What You Will Do Step by Step

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1. Learn the basic ideas behind seismic waves and velocity. 2. Study how refraction and reflection surveys are designed. 3. Use simple synthetic examples to illustrate anisotropy. 4. Outline a data-processing plan for joint analysis. 5. Interpret potential results in terms of rock types and faults. 6. Consider practical limitations and data quality issues.

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Expected Outcome

A clear, student-friendly explanation of how seismic velocity anisotropy can inform reservoir characterization, plus a basic plan for applying the approach to real data. The project should help students understand why considering anisotropy matters in faulted basins and how combining refraction with reflection improves confidence in the results.