In-situ Microscopic Visualisation Study

1. Overview

In-situ microscopic visualization study is an advanced experimental technique that allows direct observation of fluid–fluid and fluid–rock interactions under reservoir-representative temperature and pressure conditions.
By integrating optical microscopy, infrared or Raman spectroscopy, and high-pressure visual cells, the method enables researchers to visualize phase behavior, interfacial phenomena, and solid deposition processes at the pore or droplet scale.

This approach is widely applied in CO₂-EOR, CCUS, and reservoir engineering research to study dynamic processes such as miscibility development, asphaltene/wax precipitation, CO₂ dissolution, and wetting alteration, which cannot be captured by bulk PVT experiments alone.

2. Principle and Experimental Concept

The core principle of in-situ microscopic visualization lies in the use of transparent high-pressure optical cells (e.g., IRHPOC – Infrared High-Pressure Optical Cell or fused-silica capillary cell) that simulate reservoir pressure and temperature while allowing real-time optical access through sapphire or quartz windows.

  • Pressure and temperature control:
    Achieved via precision pumps and thermostatic heating systems, typically up to 150 MPa and 200 °C.

  • Optical observation:
    Conducted under transmitted or reflected light microscopy, infrared imaging, or Raman microprobe analysis to record visual and spectroscopic data simultaneously.

  • In-situ operation:
    Fluids (oil, brine, CO₂, or chemicals) are injected into the sealed optical cell, where real-time images are captured during injection, dissolution, or phase transition processes.

The in-situ nature of the experiment ensures that phase evolution and interfacial changes are monitored without depressurization or sampling disturbance, preserving the system’s thermodynamic equilibrium.

3. System Configuration

A typical in-situ microscopic visualization system includes:

  • High-pressure optical cell (IRHPOC or HPOC): designed with sapphire/quartz windows for optical and IR access, volume 0.5–5 mL, pressure rating up to 150 MPa.

  • Temperature control stage: Linkam-style heating–cooling system for precise temperature stability (±0.1 °C).

  • Syringe or piston pumps: to regulate CO₂ or fluid injection at controlled rates.

  • Optical microscope or Raman system: equipped with high-resolution CCD/CMOS camera, objective lenses (5×–100×), and optional infrared or Raman modules.

  • Data acquisition and image analysis software: for real-time visualization, image processing, and spectral analysis of phase changes and solid formation.

4. Experimental Applications

  1. CO₂–Crude Oil Interaction Studies:
    Visualization of gas dissolution, droplet shrinkage, and interfacial tension evolution during miscibility development.

  2. Asphaltene and Wax Precipitation:
    Direct observation of particle nucleation, growth, and flocculation under pressure depletion or CO₂ contact.

  3. Surfactant or Nanoparticle EOR Studies:
    Monitoring wettability alteration, emulsion formation, and interface stabilization at the micro-scale.

  4. CO₂–Water–Rock Interaction (CCUS):
    Tracking mineral dissolution, precipitation, and interfacial gas trapping in carbonate and shale samples.

  5. Phase Behavior Analysis:
    In-situ determination of bubble-point, dew-point, and asphaltene onset pressure (AOP) using optical and spectroscopic signals.

5. Data and Interpretation

The recorded visual and spectral data provide multi-dimensional insights, including:

  • Interfacial tension and contact angle evolution (wettability effects).

  • CO₂ solubility and diffusion rates in crude oil or brine.

  • Phase morphology transitions (liquid–liquid separation, gas nucleation, emulsification).

  • Kinetics of asphaltene or wax precipitation.

  • Spectral indicators (Raman/IR peaks) for identifying specific chemical or phase changes.

These results are often correlated with PVT, slimtube, or core-flooding experiments to establish a comprehensive understanding of EOR mechanisms.

6. Advantages

  • Direct visualization of micro-scale processes under realistic reservoir conditions.

  • Simultaneous optical and spectroscopic observation (IR/Raman) for compositional insight.

  • Real-time, non-destructive monitoring of multiphase behavior and solid formation.

  • Quantitative correlation with macroscopic measurements (IFT, MMP, AOP).

  • Flexible experimental design, adaptable for oil, gas, CO₂, and chemical systems.

7. Summary

In-situ microscopic visualization study bridges the gap between microscopic mechanisms and macroscopic flow behavior in complex reservoir systems.
By capturing real-time visual evidence of phase transitions, interfacial phenomena, and solid deposition, it provides essential mechanistic understanding for CO₂-EOR optimization, CCUS integrity evaluation, and flow assurance research.

The combination of optical imaging, Raman/IR spectroscopy, and high-pressure cell technology makes in-situ visualization a powerful diagnostic tool for advancing modern petroleum and energy transition research.