How Geologists Analyze Petroleum Fluid Inclusions
Fluid inclusions are small encapsulations in of liquids or gases that are trapped within a crystal. Sometimes the fluids become trapped while the crystal is being formed. Fluid inclusions can also occur later in time when the crystal undergoes fracturing and rehealing, and the small drops are trapped.
Fluid inclusions are used in petrography and geological science for several applications, including gem analysis1 and mineral exploration.2 For the petrochemical industry, detecting petroleum fluid inclusions is a powerful way of locating and assessing new oil and gas fields.
As offshore drilling is an immensely laborious, expensive, and risky process, many oil and gas field operators will use analysis of petroleum fluid inclusions alongside other monitoring techniques to assess the viability and yield of a potential new field site. Evaluation of petroleum field inclusions can reveal a great deal of information about the geological history and site formation.3
There are a number of analytical science techniques that are used by the oil and gas industry in the analysis of fluid inclusion. These analysis methods are a variety of spectroscopic approaches, microthermometric analysis mass spectrometry, and more destructive approaches to the crushing and composition analysis of the sample of interest.3
Methods
Some of the key elements of petroleum fluid inclusions that are of interest are the textures, composition, the pressure-volume-temperature properties, and the pressure-temperature of trapping. Having a full geological analysis of an inclusion means that more than just the presence or absence of an inclusion in the crystal can be confirmed. The size and shape of the inclusion can be profiled, as well as the chemical profile and composition of what is in the inclusion.
Here is a subset of some material science approaches to studying petroleum fluid inclusions.
Microthermometric analysis
This type of analysis uses information on the temperature at which certain phase changes occur in the inclusion and can be used to extract a history of the crystal or rock growth, including when the inclusions were formed. This analysis can be paired with microscopy or imaging approaches to visualize the behavior of the trapped petroleum.
Fluorescence
Fluorescence microspectroscopy is a particularly widely used method to study petroleum inclusions specifically that offers a non-destructive geological analysis. As many chemical compounds in oil have extended aromatic systems, they often have good optical absorption and strong emission spectra. The emission wavelengths and yields can be used to identify whether petroleum is present, quantify the amount, and identify the chemical profile.
Infra-red or Raman microspectroscopy methods may also be used, either as an alternative or a complementary technique to visible fluorescence. Both techniques are sensitive to the vibrational structure of the molecule and can recover so-called ‘fingerprint’ spectra for quantification and qualitative analysis of unknown chemical species.
Modeling
Pressure volume temperature (PVT) experiments and analysis are one approach to evaluating oil conditions and can be used to recover some information on how long it takes the fluid to migrate through the rock and, therefore, how porous the material is. Now, advances in material science mean that it is often sufficient to use model data rather than necessarily performing more and more experiments on potential samples.
PVT analysis can also be useful in deciding a drilling strategy for the site and what angle and approach should be most straightforward in efficiently extracting oil or gas. PVT analysis in geology can also be used to learn about pore structures.
CRAIC Technologies
One instrumental option for petroleum inclusion characterization and other petrochemical applications is the microspectrometer range from CRAIC Technologies.
CRAIC Technologies are specialists in the development of microanalysis instrumentation for methods such as fluorescence, Raman and UV-vis-NIR microspectroscopy. Capable of analyzing samples less than a micrometer in size, the CRAIC microspectrometer range offers a powerful suite of tools for the analysis of petroleum inclusions. Most inclusions are on the micrometer scale, so this spectrometer range is uniquely well-suited to the problems faced by the oil and gas industry.
Whether you are looking to better source new oil and gas fields or whether you have more general geology, petrography or petroleum analysis, contact CRAIC Technologies to see how their microspectrometers could benefit you.
References and Further Reading
- Raneri, S., Barone, G., Mazzoleni, P., Bersani, D., & Gem, A. (2020). Non-destructive spectroscopic methods for gem analysis: a short review. 2020 IMEKO TC-4 International Conference on Metrology for Archaeology and Cultural Heritage, October, 501–506. https://www.imeko.org/publications/tc4-Archaeo-2020/IMEKO-TC4-MetroArchaeo2020-095.pdf
- Moon, K. J. (1991). Application of fluid inclusions in mineral exploration. Journal of Geochemical Exploration, 42, 205–221. https://doi.org/10.1016/0375-6742(91)90068-6
- Volk, H., & George, S. C. (2019). Using petroleum inclusions to trace petroleum systems – A review. Organic Geochemistry, 129, 99–123. https://doi.org/10.1016/j.orggeochem.2019.01.012
