Integrated Seismic-Gravity Inversion for Subsurface Fluid-Content Estimation in Fractured Reservoirs

Project Abstract

This study presents an integrated seismic-gravity inversion framework to estimate subsurface fluid content in fractured reservoirs, leveraging multi-physics data to improve the resolution and reliability of reservoir characterization. The methodology combines rock-physics-informed Bayesian inversion, joint attribute analysis, and sparse-regularized optimization to jointly invert seismic reflection data and gravity anomalies for porosity, fluid saturation, and fracture density. High-fidelity forward models are developed to capture anisotropic velocity and density contrasts introduced by fractures, fluid substitution effects, and fluid mobility heterogeneity within fractured media. The seismic component utilizes multi-offset, broadband data to extract impedance and anisotropy parameters, while gravity data provides sensitivity to density variations tied to pore-fill and mineralogy at multiple depths. A hierarchical inversion scheme is employed to mitigate non-uniqueness by incorporating prior information from well logs, core samples, and regional geology, enabling robust separation of fluid effects from lithology and porosity. Regularization strategies, including total-variation and sparsity-promoting priors, are adapted to preserve sharp fault and fracture boundaries while suppressing noise amplification. The integrated approach exploits cross-gradient constraints to enforce consistency between seismic attributes and gravity-derived density models, and employs a joint misfit objective with dynamic weighting to balance data fidelity against geologic plausibility. A Bayesian framework quantifies uncertainty in estimated fluid content and fracture networks, producing probabilistic maps of fluid-saturated zones, fracture connectivity, and potential sweet spots for extraction. Case studies on synthetic fractured reservoirs demonstrate improved vertical and horizontal resolution of fluid content compared to single-physics inversions, particularly in complex lithologies where fractures dominate the porosity structure. Application to field data highlights the method’s ability to identify hidden fracture corridors, estimate fracture density correlated with permeability, and delineate bends and intersection zones that govern fluid flow paths. Sensitivity analyses reveal the dominant data types and wavelength regimes that constrain fracture attributes, guiding survey design for optimized data acquisition. The work advances geophysical inversion by integrating seismic and gravity in a coherent framework, bridging the gap between conventional lithology-driven models and fluid-focused reservoir characterization. Implications for exploration and production include more accurate estimation of recoverable reserves, improved placement of horizontal and multistage wells, and enhanced risk assessment for enhanced oil recovery and CO2 sequestration projects. The proposed methodology is adaptable to different reservoir settings, scales, and acquisition configurations, with potential extension to incorporate additional datasets such as electromagnetic responses and surface deformation measurements, further enriching the subsurface fluid-content assessment in fractured depositional and carbonate systems.

Project Overview

What This Project Is About

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This project investigates how to combine information from seismic surveys (sound waves in rocks) and gravity measurements to estimate how much fluid (like oil, water, or gas) is present in fractured rock formations. The goal is to create a clearer picture of underground fluids by using both types of data together, rather than separately.

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The Problem It Addresses

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Objectives of the Project

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1. Learn how seismic and gravity data reflect underground fluids and rocks.
2. Develop a simple method to fuse both data types for better estimates.
3. Test the method on synthetic (made-up) and real data examples.
4. Evaluate how data quality affects results and outline limitations.
5. Provide guidance for practical field use in exploration.

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What You Will Do Step by Step

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1. Review basic concepts of seismic surveys, gravity measurements, and fractures in rocks.
2. Gather or simulate combined seismic and gravity datasets.
3. Implement a straightforward data fusion approach suitable for beginners.
4. Run tests on sample data and compare results with known answers.
5. Analyze the sensitivity to noise and data gaps.
6. Document procedures, results, and potential improvements.

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Expected Outcome