Case study · Geoscience & subsurface studies

Ultra-low flow measurement: a custom thermo-osmosis test bench for porous media

For a national geoscience research institute, IRIAN Mecatronics designed and built a custom test bench to quantify extremely slow water transport through claystone samples. The equipment applies a controlled thermal gradient to a core under confining pressure, measuring flow rates as low as 20 microliters per day with nanoliter-scale resolution.

Client: National geoscience research institute
Field: Geosciences, geological storage
Technique: Micro-flow measurement, thermo-osmosis, permeability

01 — The research question

How to measure microliter-per-day flow through tight rock samples?

Quantifying extremely slow liquid flow through tight porous media is a recurring challenge in geosciences, civil engineering, and membrane studies. To yield reliable data, the measurement must remain stable for weeks or months under controlled pressure and temperature.

The project's goal was to measure water transport through claystone samples subjected to a temperature gradient, to validate safety models for deep geological storage. The standard solution, continuous weighing of reservoirs, was prohibitively expensive and too sensitive to environmental disturbances (vibrations, air drafts) to ensure stable measurements over such a long period.

Achieving a volume measurement resolution in the nanoliter range with multi-month stability, without using expensive weighing systems that are sensitive to their environment.

02 — Our approach

Our approach: from physical principle to reliable equipment

To achieve the required stability and resolution for tests lasting several months, our in-house engineering team made three key design choices, from the flow measurement method to the control of boundary conditions.

Measuring volume by mechanical displacement

Since the flow rate was too low for standard flowmeters, we ruled out continuous weighing as too expensive and unstable. We opted for direct volume measurement based on the displacement of two high-precision positive displacement pumps. This method provides nanoliter resolution and absolute stability over several months, as it is immune to lab disturbances.
Creating a thermal gradient at the core of the cell

To study thermo-osmosis, we needed to apply a stable temperature gradient across 10 mm of rock. External heating would have been uniform. We therefore integrated independent heating systems into the platens in contact with each face of the sample. This allows the user to control a precise, asymmetrical thermal profile.
Ensuring stable confining pressure

The test's validity required a constant, isostatic confining pressure, which a simple pressure reducer cannot provide. We designed a gas booster circuit with a buffer volume and fine control using a piloted back-pressure regulator. The cell is thus isolated from source fluctuations, ensuring the sample's integrity.

03 — Beyond this project

Is this technology right for your project?

Civil engineering and construction materials

The principle of flow measurement using positive displacement pumps can be adapted to measure water permeability or the diffusion of aggressive agents in high-performance concrete. Only the test cell would need to be modified for larger samples and more corrosive fluids.

Membrane technologies and fuel cells

The high-precision pump system is also suitable for characterizing gas or liquid permeation through membranes. The cell design would be adapted for flat membranes, and materials would be selected for compatibility (e.g., hydrogen, methanol).

Pharmaceuticals and medical devices

This ability to measure minute volume changes is directly applicable to studying the very slow release of an active ingredient from a solid matrix. The test cell would be redesigned as a biocompatible diffusion chamber using medical-grade materials.

04 — Specifications

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

Show specifications · Ø 40 mm x 10 mm · 50 bar (725 psi) · 30 bar (435 psi)

Technical specifications — Ultra-low flow measurement: a custom thermo-osmosis test bench for porous media
Sample dimensions	Ø 40 mm x 10 mm
Maximum confining pressure	50 bar (725 psi)
Maximum injection pressure	30 bar (435 psi)
Maximum operating temperature	40°C (104°F)
Flow rate range	1.10⁻⁶ to 0.08 mL/min
Volume measurement resolution	0.000001 mL (1 nL)
Pressure measurement resolution (fluid)	0.001 bar (0.015 psi)

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 type of permeability bench be used with organic or corrosive fluids?

Yes, the measurement principle using positive displacement pumps is fluid-independent. For organic or corrosive fluids, our engineering team would adapt the wetted materials: seals, tubing, and the bodies of the pumps or the cell (Hastelloy, titanium, PEEK). The design remains the same as long as the fluid's viscosity is compatible with the pump mechanics.

Is it possible to measure higher flow rates while maintaining high resolution at low flow rates?

Yes, that is one of the advantages of positive displacement pump systems. By selecting pumps with a larger cylinder volume, the maximum flow rate can be significantly increased. The resolution, which depends on the motor's encoder, remains at the nanoliter scale. This approach is often used for tests that require a rapid, high-flow saturation phase, followed by a very low-flow permeability measurement.

How can this equipment be adapted for larger samples or different geometries?

The control architecture (pumps, pressure and temperature regulation) is independent of the test cell. For larger samples, we would design a custom mechanical cell, potentially larger and with adapted heating and pressure systems. Our HPHT triaxial testing systems are a good example of this adaptation to standard rock geometries.

Can the system operate in constant pressure mode instead of constant flow rate mode?

Absolutely. The system is controlled by a PLC that allows for both control modes. In 'constant pressure' mode, the PLC continuously adjusts the pump flow rate to maintain a constant pressure upstream and downstream of the sample. The resulting flow rate becomes the test measurement, which is the typical mode for permeability tests.

Is your permeability or micro-flow measurement limited by the resolution or stability of your current equipment?

Describe your challenge, pressure and temperature conditions, and the fluids involved. Our engineering team will analyze your project's feasibility and get back to you with a proposed approach.

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