Bringing Rock Physics Into Everyday Seismic Interpretation With SubsurfaceAI

Rock physics is the scientific foundation that links subsurface reservoir properties—porosity, lithology, fluids, pressure—to the seismic responses we observe in the field. Yet for most seismic interpreters, rock physics has been perceived as an advanced, specialist-only domain. Historically, performing rock physics modeling meant turning to specialized software, running complex scripts, or consulting an in-house or external expert.

SubsurfaceAI changes this paradigm completely.

With the introduction of the Rock Physics Modeling (RPM) module—designed and coded entirely by geophysicists for geophysicists—SubsurfaceAI brings rock physics directly into the interpreter’s daily workflow. No coding. No PhD-level rock physics expertise. No external tools. No black-box behavior.

Just intuitive, guided rock physics modeling that any seismic interpreter can use.

This article is Part 1 of a 5-Part Series showcasing how SubsurfaceAI makes rock physics accessible, practical, and repeatable through a modern, interpreter-friendly interface.

Introducing the Five-Part Rock Physics Modeling Series

Part 1 (this article):

Why rock physics belongs in the interpreter’s workflow & a detailed overview of the RPM models included in SubsurfaceAI.

Part 2:

Using RPM and Rock Physicist Templates (RPTs) to generate Vp–Vs–Density and synthetic seismic from static/dynamic reservoir models.

Part 3:

Converting inversion results (Vp–Vs–Density) into porosity, lithology, and fluid saturation volumes using RPTs.

Part 4:

How machine learning (ML) simplifies, accelerates, and scales rock physics workflows.

Part 5:

Performing quantitative “What-If” seismic analysis (thickness, N:G, saturation scenarios) with interactive synthetic seismic.

Why Seismic Interpreters Need Rock Physics—Now More Than Ever

Seismic interpreters face physically-based questions every day:

• Is this amplitude anomaly fluid-related or lithology-driven?
• Is this brightening real, or just tuning?
• Why is the well tie perfect here but off by 10 ms over there?
• Why does this Vp/Vs low occur? Gas, porosity, or rock type?
• What does this inversion shade of blue actually mean in reservoir terms?

These questions live at the intersection of rock, fluid, and wave propagation physics.

Unfortunately, most interpreters lack direct access to modern rock physics tools. Instead, they must rely on:

• Specialist rock physics software
• Petrophysicists or QI teams
• Homemade MATLAB/Python scripts
• Occasional consultant studies
• Incomplete inversion interpretation rules

This leads to delays, miscommunications, inconsistencies, and incomplete understanding.

SubsurfaceAI eliminates these barriers.

Rock Physics for Everyone: Designed by Geophysicists, for Geophysicists

The RPM module in SubsurfaceAI was intentionally built around the workflows of practicing interpreters, not around the academic or specialist workflows common in traditional rock physics packages.

Key Design Principles

1. No coding required—ever.
   Everything is built into guided interfaces and forms.
2. Intuitive for interpreters.
   If you can QC logs or run an inversion, you can run RPM.
3. Fully integrated with the interpretation workflow.
   No exporting, no external apps, no tool switching.
4. Transparent rock physics.
   No black-box equations—you see exactly what physical models are used.
5. Consistent across teams.
   RPTs enable shared, reusable, standardized rock physics practices.
6. Workflows written and coded by working geophysicists.
   The entire system was designed by professionals who understand real seismic interpretation—not by mathematicians or coders unfamiliar with interpretation needs.

How This Differs From Traditional Rock Physics Software

Most rock physics tools today fall into two categories:

1. Academic or research software
   • Complex interfaces
   • Designed for rock physicists, not interpreters
   • Little connection to interpretation or seismic workflows
   • Require theory knowledge and parameter tuning expertise
2. Specialist commercial tools
   • Powerful but inaccessible
   • Expensive licenses
   • Used by dedicated QI or rock physics teams
   • Not integrated into interpretation software

SubsurfaceAI’s RPM module is neither.

It is the first fully integrated, interpreter-friendly rock physics environment built to serve the needs of everyday seismic interpretation.

A Comprehensive, Interpreter-Friendly Rock Physics Library

SubsurfaceAI includes a full library of industry-standard rock physics models. These are the same models specialists use—but simplified, structured, and automated for interpreters.

Below is a detailed overview of the rock physics capabilities included natively.

1. Fluid Substitution Models

Gassmann Fluid Substitution

SubsurfaceAI includes a complete implementation of Gassmann’s equations:

• Brine ↔ Oil ↔ Gas substitutions
• Patchy vs. uniform saturation
• Frequency-dependent saturation effects
• Pressure- and temperature-adjusted fluid properties
• Full support for hydrocarbon mixtures
• Handles unconsolidated to consolidated rocks

Interpreter Benefits:
You can run fluid substitutions on your logs in seconds—no equations, no scripting.

2. Empirical Velocity–Porosity–Lithology Transformations

Castagna’s Mudrock Line

Shale vs. sand discrimination and gas-sand deviations.

Han et al.’s Sandstone Model

Velocity trends as functions of porosity and clay content.

Raymer–Hunt–Gardner Transformations

Density–porosity relationships.

Gardner’s Density–Velocity Relation

Useful for quick-check density estimates.

Interpreter Benefits:
These models help anchor inversion results and crossplots in physical reality—even with limited well data.

3. Effective Medium and Mixture Models

These models handle complex rock types and lithology mixes.

DEM (Differential Effective Medium)

SCA (Self-Consistent Approximation)

Xu-White and Modified Xu-White Models

Dvorkin’s Soft-Sand and Stiff-Sand Models

Cemented Sand Models

Crack/Aspect Ratio Models

SAI models the full spectrum of rock framework conditions:

• Unconsolidated sands
• Burial compaction
• Cementation and diagenesis
• Shaly sands
• Mixed lithologies
• Carbonates with complex pore geometries

Interpreter Benefits:
You can use realistic, physically-based rock models for your reservoirs—even if you are not a rock physics expert.

4. Mineral & Fluid Mixing Models

Voigt, Reuss, Hill Average

Hashin–Shtrikman Bounds

Ternary Mixtures (sand–shale–carbonate)

These models allow interpreters to:

• Estimate elastic moduli of mixed lithologies
• Derive bounds for uncertain mineral mixtures
• Handle variable Vshale and heterogeneity

5. Saturation Models

Patchy and Uniform Saturation

Partial Gas Saturation

Waterflood/Depletion Modeling

These enable predictive modeling of:

• Waterflood fronts
• Gas exsolution
• Residual oil
• 4D seismic effects

6. Anisotropy and Stress-Sensitive Elasticity

SAI supports:

• Stress-dependent velocities
• Overpressure effects
• Simplified crack density models
• VTI/HTI approximations using aspect ratios

These help interpreters understand seismic anomalies associated with stress or fracture systems.

SubsurfaceAI Makes Rock Physics Truly Interpreter-Friendly

Most rock physics software requires:

• Building scripts
• Managing complicated parameter sets
• Running code to visualize results
• Exporting/importing between multiple tools
• Advanced rock physics theory knowledge

SubsurfaceAI removes all of these barriers.

No Coding Required

Every rock physics workflow—fluid substitution, velocity modeling, facies clustering, synthetic AVO—is run through point-and-click interfaces.

Guided Panels

Interpreters follow simple, structured steps:

1. Select logs
2. Choose model
3. Adjust parameters
4. Preview results
5. Save as an RPT

Instant Crossplots and Feedback

SubsurfaceAI visualizes results immediately:

• Vp–Vs–Density crossplots
• Porosity trends
• AVO reflectivity plots
• Synthetics and angle gathers

Integrated With Interpretation Data

You work directly with:

• Well logs
• Horizons
• Seismic volumes
• Inversion results
• Reservoir models

No exporting. No third-party tools. No friction.

Rock Physicist Templates (RPTs): Making Rock Physics Reusable and Consistent

The RPT system is one of SubsurfaceAI’s most important innovations.

An RPT is a fully encapsulated rock physics model that includes:

• Chosen model (DEM, Xu-White, Mudrock, etc.)
• Calibrated parameters
• Porosity–velocity trends
• Fluid properties
• Mineral moduli
• Saturation assumptions
• QC rules
• Facies definitions

Once created, interpreters can:

• Reapply RPTs to new wells
• Use them for inversion-to-property prediction (Part 3)
• Apply them to reservoir models for synthetic seismic (Part 2)
• Use them in advanced What-If analyses (Part 5)
• Share them across teams to standardize rock physics practices

RPTs make rock physics repeatable, reliable, and collaborative.

Where RPM Fits Into Everyday Interpretation Workflows

1. Well Ties and Wavelet QC

RPM helps interpreters diagnose:

• Why a tie works or fails
• Whether wavelet assumptions are valid
• If elastic or fluid effects explain observed misfits

2. AVO Interpretation

RPM clarifies:

• Whether AVO behavior fits expected fluid/lithology patterns
• If anomalies are real or artifacts
• Which class of AVO to expect for a given sand/facies

3. Interpreting Inversion Volumes

RPM connects:

• Vp/Vs patterns → lithology
• Density variations → fluids
• Impedance trends → porosity & net-to-gross

4. Understanding Uncertainty

RPM lets you test:

• Fluid variations
• Porosity ranges
• Mineralogy uncertainties
• Compaction differences

5. Seismic Amplitude Explainability

You can now answer:

• Why does this amplitude exist?
• What reservoir property drives it?
• What would change the amplitude?

How SubsurfaceAI Differs From Any Other Rock Physics Software

SubsurfaceAI RPM: Built for Interpreters

• No scripting
• No theory deep dives
• No external tools
• No complex setup

Traditional Rock Physics Software: Built for Specialists

• Coding and scripting required
• Difficult parameterization
• Designed for researchers
• Poor integration with seismic interpretation

Conclusion: Rock Physics Is Now a Daily Interpretation Tool

SubsurfaceAI makes rock physics:

• Accessible – interpreters can run RPM without specialized training
• Integrated – directly within seismic interpretation and inversion workflows
• Repeatable – via standardized RPT templates
• Scalable – with ML-assisted workflows (Part 4)
• Scenario-driven – with interactive What-If capabilities (Part 5)

This marks a significant evolution: rock physics is no longer a bottleneck or specialist-only discipline. It becomes a powerful, intuitive component of the seismic interpretation workflow—helping interpreters make better, faster, more confident subsurface decisions.