Fluid inclusions analysis for resource exploration

Fluid inclusions are small bubbles of water, oil or gas trapped within the minerals of various geological formations. As geoscientists, we understand the significance of this technique in uncovering the secrets buried within rocks and various fluid resources. They provide valuable information about the conditions under which geothermal fluids, oil & gas, lithium, and natural hydrogen formed, the properties of the fluids (pressure, temperature, composition), and the associated geochemical processes. By analysing fluid inclusions, we can better understand the composition, origin, and production potential of these resources. This enables us to optimise exploration strategies, make informed decisions, and maximize the chances of successful discoveries.

How does the energy industry analyse fluid inclusions?

How does the industry analyse fluid inclusions ?
Figure 1.  Various industry’s techniques for analysing fluid inclusions. The Statistics of Distribution, or Fluid Inclusion Stratigraphy (FIS) method involves analysing fluid inclusions (FI) for density and depth distribution using bulk counting and GC-MS. This may provide insights into paleo oil-water contacts. The Chemistry method assesses the chemical composition of fluid inclusions using biomarkers through GC-MS, IRMS and LA-ICPMS, helping to determine the composition, oil source, and evolution. The Thermodynamics method analyses the PVT (Pressure-Volume-Temperature) properties of fluid inclusions non-destructively to determine the PT conditions of trapping. Isochores are used to identify the trapping temperature and pressure. Photomicrographs depict oil fluid inclusions under UV light, aiding in hydrocarbon identification.

A more in-depth description of the thermodynamic method.

The individual fluid inclusion thermodynamic method involves analysing the thermodynamic properties, temperature of phase changes, and composition of a series of individual fluid inclusions (n±20) found within a given mineral. To achieve this, we need to follow the precise workflow described in figure 2 and in the text below. This workflow outlines the detailed steps required for the P-V-T evaluation of fluid inclusions, ensuring a comprehensive analysis from petrography to basin modeling and petroleum systems analysis.

Detailled workflow thermodynamic evaluation
Figure 2. Analytical workflow for fluid inclusion thermodynamics characterisation.  This state-of-the-art analytical approach aims to reconstruct temperature, pressure and composition of fluids inclusions entrapped without various host minerals.  All analytical steps are detailed in the text below.

Petrography of fluid Inclusions – their relationship to the host mineral

Studying fluid inclusion petrography is a crucial first step before performing microthermometry or Raman spectroscopy. Petrography allows for the identification and characterisation of the inclusions, determining their nature, distribution, and relationships within the host mineral.

Fluid inclusion pertrography
Figure 3. Fluid inclusion pertrography. These pictures display the THMS 600 heating-cooling stage and associated microscope used for fluid inclusion analyses, along with a photomicrographs of petroleum fluid inclusions observed under UV light, an artistic view of aqueous, oil and gas inclusions, as well a sketch illustrating a co-assemblage of oil and aqueous inclusions in a quartz overgrowth. UV fluorescence is largely derived from aromatic compounds and eases the identification and analysis of petroleum inclusions within geological samples.

Below are the various analytical steps for precise characterisation of fluid inclusions petrography.

  • Paragenesis and mineral mapping – Determining diagenesis events and chronology using cathodoluminescence techniques and HR imaging/microcopy.
  • Description of fluid inclusion assemblages and their relationship to the host mineral
  • Locating fluid inclusion assemblages: within the detrital or ancient core, in overgrowth zones, or in fractures, identify the primary vs secondary nature of assemblages.
  • Tracking petroleum fluid inclusions using UV fluorescence
  • Identifying coexisting aqueous and petroleum inclusions (trapped simultaneously)

Microthermometric Measurements – temperature and salinity evaluation

Our goal is to reconstruct the P-T-t conditions of fluid entrapment during diagenesis, understand the conditions of fluid and gas migration and storage, evaluate leakages, and date all these events, providing crucial information about the thermodynamic and geochemical conditions prevailing during the formation of the inclusions and the precipitation of the host minerals. Microthermometry involves heating/cooling the inclusions and observing the precise temperatures (±0.1°C cold and ±0.5°C hot) at which the phase changes occurred within the inclusion:

  • Measurement of homogenisation temperature (Th) (minimum trapping temperature)
  • Measurement of ice melting temperature (Tm ice) (salinity)
  • The phase transition (L1+L2+V -> L+V) in fluids reveals the presence of gas condensates
  • Measurement of final melting temperature of carbonated phases (Tm car) (-56.6°C for pure CO2) (gas identification in the bubble phase)
  • Measurement of eutectic temperature (Te) (NaCl-KCl-CaCl2-LiCl…)
Microthermometric analysis
Figure 4. Microthermometric analysis. This figure illustrates the petrography and phase changes of aqueous and petroleum fluid inclusions during microthermometric measurements. The inset reveals a detailed sketch of coeval petroleum (green) and aqueous (blue) inclusions entrapped in a quartz overgrowth. The histogram displays homogenization temperatures of the inclusions: aqueous (blue), oil (green), and gas (red).
Raman spectra
Figure 5. Raman spectra. Example of raman spectroscopy characterisation of various gases entrapped in fluid inclusions (e.g. CH4, H2O, N2, CO2, H2S, H2 etc). The letter depicted on fluid inclusions photomicrographs corresponds to the different raman spectra show below (A,B,C,D).

Raman Spectroscopy – Gas composition

By shining light on gaseous inclusions and measuring the scattered light, Raman spectroscopy provides a unique fingerprint of the composition of gas molecules present. This method allows for the precise quantification of various gases, such as methane and CO2 within the fluid inclusions. Its non-destructive nature and high sensitivity make Raman spectroscopy valuable for understanding the composition and conditions under which gaseous and petroleum inclusions formed in geological formations.

  • Characterisation of dissolved gases (CH4, CO2, H2S, H2, O2, N2)
  • Quantification of dissolved CH4 and CO2
  • Determination of properties (HCO3-, CO3=, HS-, SO4=, HSO4-,…)
  • Evaluation of the presence of contaminants (H2S) or undesirable species in fluid inclusions that could affect the quality and economic viability of resources.

Confocal Microscopy – toward 3D imaging of petroleum inclusions

Confocal scanning laser microscopy is used to determine the Gas Volume % (Fv) of individual fluorescent oil inclusions; Fv varies with temperature and is a characteristic of oil chemistry and maturity. It serves as an input parameter for thermodynamic modelling. Fv vs Th  graphs can be created for petroleum inclusion and help us to determine the hydrocarbon types entrapped in the inclusion: e.g. black oils, heavy oils, light oils, critical oils, gas condensates, wet gas, and dry gas.

Figure 6. Z-stacks of confocal images are used to create a 3D volume of fluid inclusions. The resulting 3D reconstruction allows for the identification and volumetric measurement of different phases within the inclusion, such as gas (red) and oil (green).

P-V-T-X-t Thermodynamic Modelling (pressure, volume, temperature, composition and timing)

The superposition of isochores from different fluid inclusions (aqueous, oil and/or gas) is the only method to provides the true trapping temperature and pressure, at the intersection point. The thermodynamic modelling of aqueous inclusions (with dissolved CH4) is based on Zhang & Frantz’s equation of state (H2O-NaCl system) and Duan & Mao’s thermodynamic model. The thermodynamic modelling of other fluid inclusions is based on the appropriate equations of state (e.g., Peng-Robinson for hydrocarbons).

Analysis of petroleum fluid inclusions
Figure 7.  Analysis of petroleum fluid inclusions (AIT/PIT method), showing how oil charge conditions in the reservoir were reconstructed. The central graph illustrates isochores of oil and aqueous inclusions, intersecting here at 98°C and 410 bars. Photomicrographs under UV light show fluorescence of petroleum inclusions, aiding hydrocarbon identification. The mineral paragenesis chart outlines the entire sequence of mineral formation and replaces the oil charge timing in a diagenetic framework.

Integration into basin/reservoir models – A proper geomodel should fulfil all analytical data.

The trapping P-T conditions recorded in fluid inclusions enable estimation of fluid overpressure episodes, crucial for understanding migration pathways, cap rock integrity, and episodic fluid expulsion.

These insights are vital for basin evolution and reservoir performance. AIT (Aqueous Inclusion Thermodynamic) and PIT (Petroleum Inclusion Thermodynamic) methods also provide precise temperature estimate (e.g. to trace hydrothermal condition), dating of ancient fluid events, establishing a detailed timeline of interest fluid generation, expulsion, migration pathways, and trap formation.

Integrating this data into 1D basin (e.g. on PetroMod) modelling offers a comprehensive view of fluid-related events over geological timescales, aiding in better exploration and production strategies. This combined approach improves the accuracy of basin models, ensuring more effective prediction and management of resources.

Example of temperature-pressure
Figure 8. Example of temperature-pressure (T-P) paths over time reconstructed based on AIT/PIT fluid inclusions analysis. The black line with squares represents the modelled pressure-temperature evolution in hydrostatic and lithostatic conditions of the reservoir through time, with key time markers at 24.2, 22.4, 10.3, 6.8, and 0 million years (Ma). Isochores for petroleum inclusions (green lines) and aqueous inclusions (blue lines) are also plotted. Assemblage 1, Assemblage 2 indicates distinct fluid inclusion assemblages (measured in different minerals of a paragenesis) trapped along the T-P path experienced by the reservoirs. The square, arrows and annotations illustrate temperature-pressure (and overpressure relative to hydrostatic) evolution in the reservoir’s history

Comprehensive fluid inclusion analytical services offered by H-Expertise Service

Summary of our workflow used for routine petroleum fluid inclusions analyses.
Summary of our workflow used for routine petroleum fluid inclusions analyses.

This workflow illustrated below can be readjusted according to client needs to match specific operational requirements, pricing and timelines. For pricing information on the different steps or to request a global quotation, please contact @Vanessa

Sample type needed for fluid inclusion analyses

For fluid inclusion analyses, a thick section of rock approximately 100 micrometers thick is required. This thick section can be derived from core samples, plugs, cuttings, or sidewall cores. The preparation involves cutting and polishing the rock sample to the desired thickness and mounting it on a glass slide.

In the mining and oil and gas industry, the common minerals of interest for fluid inclusion analyses include quartz, calcite, dolomite, halite, anhydrite, fluorite, barite, and siderite. As multiple minerals often co-exist in subsurface reservoir, and multiple generations of fluid inclusions can also be found within each host mineral, we can reconstruct detailed and informative P-T (pressure-temperature) history, providing valuable insights into the geological systems evolution.

Turnaround time

The delay for performing the analytical work can vary greatly depending on the scope of the project and the type of analysis requested, ranging usually from 2 weeks up to 12 months.

Contact us

At H-Expertise Services, we leverage advanced techniques, state-of-the-art equipment, and the expertise of our seasoned inclusionists with decades of practical experience to ensure you receive precise and insightful data, deepening your understanding of geological systems. Our fluid inclusion analyses provide a comprehensive view of fluid histories and geological processes. Partner with us for unmatched expertise and impactful results. Please contact our specialist, Vanessa Dyja-Person, at vanessa.dyja-person@h-expertise-services.com to discuss your operational needs, pricing, and to design a customised analytical strategy tailored to your requirements.

Recent case studies and geological projects

Interested in the practical applications of our fluid inclusion analysis services? For detailed examples of recent case studies and geological projects we have undertaken, please visit our case study section. Discover how our advanced techniques have delivered crucial insights and improved reservoir understanding for our clients.….read more here