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Reservoir and Source Rock Evaluation Services

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Real-Time Isotopic analyses δ13 C of C1, C2 and C3

GEOLOG can offer a comprehensive range of carbon isotopic analyses at well site, thanks to an innovative patented analytical solution. GEOLOG was the first company able to perform isotopic analyses from methane to propane and at the well site. This provides a continuous real-time log throughout the well, using our efficient mud gas extraction techniques for increased gas characterization and reduces risks incurred through conventional spot sample collection.

  • To identify the biogenic, mixed or thermogenic origin of gas
  • To establish the provenance of gas in cap rocks and to assess seal efficiency
  • To determine maturity of gas evaluation
  • To identify possible sources of gas
  • To assess compatibility between gas and associated oil (similar source or maturity?)
  • To detect and quantify possible mixing of gases with different origins
  • To corroborate fluid contact identification
  • To corroborate reservoir connectivity
& Solutions

Chemical analyses of gas compositions are fundamental, but sometimes these data are insufficient to fully understand gas origin, maturity and distribution.

For example, a well-sealed thermogenic gas reservoir underlying less mature or biogenic gas sourcing shales would be isotopically heavier than the gases in the overlying cap rocks. In the event the seal was leaking, the overlying gases would develop a heavier isotopic signature due to the presence of the thermogenic gases entering the seal. By recognizing these trends operators can gain a better understanding of the gas origin, being indigenous or migrated from a reservoir, through slight but continuous leakages.

To understand the origin of gas, GEOLOG utilises various published models validated by case histories and based on integration of compositional and isotopic values.


In exploration, the GeoIsotopes service can be utilized to understand the origins of oil, to identify source rocks and help confirm migration pathways.

“The advanced gas service provided by GEOLOG has proven definitely to add values to the Asset Team to narrow down uncertainties in fluid interpretation related to complexity and heterogeneity."


Case History

Identification of Carbon Origin from Methane and Ethane Isotopic Ratios

The log charts on the left identify different isotopic marking of gases detected at different well targets.
The shallower ones indicate mixing with bacterial gas. Only the lowest interval (the main reservoir target) shows a clear thermogenic origin.
On the right, the crossplots between C1 and C2 isotopic ratio show the extent of migration and alteration of the hydrocarbons.
This is only possible on site with GEOLOG’s GeoIsotope service providing continuous well data and interpretation. 


δ13C  Analysis

Methane (C1), Ethane (C2) and Propane (C3)

Limits of Detection

Minimum 500ppm to 30% of volume

Analysis Time

3 min (C1-C2), 8 min for full range