Advanced Quantitative Analysis of Seismic Parameters for Subsurface Characterization

Accurate knowledge of rock elastic properties is essential for reliable subsurface characterization in geophysical and reservoir engineering workflows. 

Elastic parameters – the basis for precise reservoir analyses

Parameters such as P-wave and S-wave velocities, compressional slowness, and acoustic impedance play a crucial role in seismic interpretation, helping to estimate lithology, identify fluid types, and monitor changes in reservoir conditions over time. These properties are especially sensitive to fluid saturation - the presence of oil, gas, brine, or CO₂ within the pore space significantly alters the rock’s elastic behavior and seismic response.

Understanding how seismic velocities vary with different fluid mixtures or saturation levels is vital for applications such as time-lapse (4D) seismic monitoring, carbon capture and storage (CCS), and enhanced oil recovery (EOR).

Physics-based simulation instead of approximation

To address this, we take a physics-based, high-resolution approach grounded in real rock microstructures. We start with micro-computed tomography (µCT) images of actual rock samples, which are segmented to distinguish between mineral matrix, pore space, and fluid phases.

Unlike traditional methods that rely on simplified rock models or empirical approximations, we apply direct numerical simulations (DNS) on the segmented 3D structures. These simulations allow us to compute elastic and acoustic properties - such as P- and S-wave velocities, compressional slowness, and acoustic impedance - with high fidelity and physical accuracy.

Seismic findings with the QSI GeoApp

This dedicated QSI-GeoApp is the computational tool that drives this workflow. It ingests segmented µCT data and performs direct simulations to predict how the rock responds to seismic waves under various fluid saturation scenarios, including brine, oil, gas, and CO₂. 

This approach provides a more realistic and detailed understanding of how fluid substitutions impact seismic signatures - enabling more accurate seismic interpretation, improved reservoir characterization, and more reliable decision-making in the field.

• Use of real Rock Structures: Works directly with high-resolution micro-CT images of real rock samples. No idealized or simplified geometries are used.
• Direct Numerical Simulations (DNS): Performs physics-based simulations directly on the segmented 3D rock structure to compute elastic and acoustic properties accurately.
• Customizable Solver Settings: Allows users to define simulation-specific parameters such as boundary conditions and the computational direction (wave propagation axis).
• Adjustable Grain Contact Stiffness: Users can set the mechanical stiffness between grains, ranging from loose to tight to fully cemented, including intermediate states.
• Simulations at one or multiple Fluid Saturations: Enables simulations with various fluid configurations such as brine, oil, gas, or CO₂.

• Output Parameters (computed at one or several fluid saturations):
  • Porosity
  • Bulk Density
  • Fluid Density
  • Solid Density
  • P-wave Velocity
  • S-wave Velocity
  • P- to S-wave Velocity Ratio
  • Compressional Slowness
  • Shear Slowness
  • Acoustic Impedance
  • Bulk Density over P-wave Velocity