Case study · Geoscience & subsurface studies

Measuring rock deformation and permeability with a custom HPHT triaxial cell

IRIAN Mecatronics designed and built a custom high-pressure, high-temperature (HPHT) triaxial test cell for a major university geoscience research center. The equipment simulates deep geological conditions (150 MPa / 21,750 psi, 150°C / 302°F) to measure rock sample deformation and permeability with micrometer resolution in the presence of corrosive fluids.

Client: Major university geoscience research center
Field: Geoscience, rock mechanics
Technique: HPHT triaxial testing, permeability measurement, mechanical characterization

01 — The research question

How to characterize a porous material's behavior under multiple stresses in a reactive environment?

Studying the mechanical and hydraulic behavior of a porous solid material like rock requires controlling several parameters at once: a confining pressure to simulate depth, an axial stress to simulate tectonic forces, a pore fluid pressure, and temperature. The study's reliability depends on the ability to maintain stable control over these parameters and to measure the resulting ultra-low deformations and flow rates.

This project aimed to replicate deep geological environments to characterize rock properties. No off-the-shelf equipment could meet all the requirements: simultaneously applying very high pressures (confining pressure up to 150 MPa, pore pressure up to 100 MPa), a high axial stress (500 MPa) at 150°C (302°F), while ensuring compatibility with corrosive fluids and guaranteeing very high measurement resolution over long-duration tests. This called for a fully custom HPHT triaxial rock mechanics cell.

Maintaining stable control and micrometer-level measurement resolution during long-term tests while subjecting the sample to extreme pressures, temperatures, and corrosive fluids.

02 — Our approach

The design approach: three key decisions to ensure measurement reliability

Achieving the target performance relied on specific design choices to overcome three main challenges: pressure stability for low flow rate measurements, chemical compatibility of the pore fluid circuit, and the accuracy of deformation measurement.

Ensuring absolute pressure stability for ultra-low flow rate measurements

Measuring very low permeability (down to 10⁻¹⁷ m²) requires perfect pore pressure stability. The chosen design ensures a perfectly continuous mass flow rate, free from the typical oscillations of single-piston systems that would skew the measurement. This stability makes it possible to quantify extremely low permeabilities and maintain constant conditions over tests lasting several weeks.
Isolating the pore pressure circuit for use with corrosive fluids

The fluid injected into the rock can be a strong acid or base, which would attack standard steels at high temperatures. The solution is to isolate this fluid in a dedicated circuit where all wetted parts are made of chemically inert materials. This allows the user to test a wide range of reactive fluids without risk of corrosion, contamination, or skewed results—a key challenge in geochemical studies with corrosive fluids.
Measuring the sample's deformation, not the machine's

An accurate measurement of rock deformation is often compromised by the compliance of the press frame and piston. To eliminate these parasitic deformations, the displacement sensor was placed as close as possible to the sample. This provides the user with a stress-strain curve that faithfully reflects the material's intrinsic behavior.

03 — Beyond this project

Does your application share similar challenges?

Energy: H₂ storage, CO₂ capture

The long-term behavior of reservoir rocks or cements in the presence of H₂ or supercritical CO₂ is a common concern. The principles of triaxial confinement, pore pressure regulation, and permeability and deformation measurement would remain the same.

Advanced materials / composites

Studying the mechanical strength and aging of materials under multi-axial stress in harsh environments presents a similar need. The principles of applying controlled stress, precision deformation measurement, and thermal control are directly transferable.

Process engineering / pharmaceuticals

When studying the compaction of powders or granules, measuring fluid permeability under high stress is a shared challenge. The principles of applying axial stress and pore pressure, along with measuring very low flow rates, remain relevant.

04 — Specifications

The values for this project. Every system is custom-built, so they adapt to your requirements.

Show specifications · Up to 150 MPa (1500 bar / 21,750 psi), accuracy ±0.2 MPa · Up to 500 MPa (5000 bar / 72,500 psi), accuracy ±0.2 MPa · Up to 100 MPa (1000 bar / 14,500 psi), accuracy ±0.2 MPa

Technical specifications — Measuring rock deformation and permeability with a custom HPHT triaxial cell
Confining pressure	Up to 150 MPa (1500 bar / 21,750 psi), accuracy ±0.2 MPa
Axial stress	Up to 500 MPa (5000 bar / 72,500 psi), accuracy ±0.2 MPa
Pore pressure	Up to 100 MPa (1000 bar / 14,500 psi), accuracy ±0.2 MPa
Temperature	Up to 150°C (302°F), extendable to 200°C (392°F), control ±1°C
Permeability measurement range	10⁻¹³ m² to 10⁻¹⁷ m²
Axial deformation measurement resolution	±1 µm
Pore volume measurement resolution	±0.001 cm³
Standard sample size	Ø 20 mm x 40 mm

IRIAN Mecatronics designs and builds custom high-pressure, high-temperature equipment for research laboratories, technical centres and industry.

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05 — FAQ

Frequently asked questions

Can this triaxial test system be adapted for temperatures above 150°C?

Yes, the equipment is designed to be extendable up to 200°C (392°F). Such an upgrade would require a review of certain material selections and sealing technologies to ensure reliability and safety at higher temperatures. The overall principle of the equipment would remain unchanged.

How does the test rig handle the injection of gases like supercritical CO₂ or hydrogen?

The pressure control and flow measurement principles can be adapted for gases. The main changes would involve the wetted materials, for instance to prevent hydrogen embrittlement, and the control algorithms to manage high gas compressibility. The safety systems would also be reinforced accordingly.

Is it possible to integrate acoustic measurements (P & S waves) into this triaxial cell?

Yes, the cell's architecture was designed to allow for the future integration of ultrasonic transducers. This requires creating specific passages and mechanical interfaces on the compression pistons without compromising the pressure rating. This is a common option on our HPHT equipment for geoscience and subsurface studies.

What is the validation process for such a complex piece of equipment before delivery?

Every custom equipment follows our ISO 9001 certified quality process. After design by our in-house engineering team and manufacturing, we perform factory acceptance tests (FAT) in our workshop. The client then visits to verify that all specifications are met before the equipment is shipped, installed, and commissioned on-site.