Source Rocks & Oils

Source Rock Geochemistry & Thermal Maturity

One of the critical events in the petroleum system is the generation of oil or gas from a source rock. To enable the generation of hydrocarbons, the source rock must meet minimum standards in terms of its geochemcial composition, this is assessed by measuring a number of screening parameters:

  • Total organic carbon (TOC) - as the name suggests, a measurement of the amount of organic carbon in a rock sample
  • Rock Eval pyrolysis - closed system pyrolysis measuring hydrocarbons evolved from a sample when heated.

Typically, samples with elevated TOC and Rock Eval S1 are most likely to have remaining hydrocarbon generative potential, samples with elevated Rock Eval S2 are likely to have either generated hydrocarbons or are stained by migrated hydrocarbons. These TOC and Rock Eval data are typically transformed into Hydrogen Index and Oxygen Index, crossplotting this data produces a Van Krevlen plot.

When suitable samples have been identified, can be further analysed to obtain more detailed information about the source and maturity of organic matter contained within the samples:

  • Extraction - amount of solvent extractable organic matter in a sample
  • Gas chromatography - technique to seperate the complex mixture of hydrocarbons in a solvent extract of a sample.
  • Gas chromatography-mass spectrometry - technique to seperate and chemically analyse the complex mixture of hydrocarbons in a solvent extract of a sample.
  • Stable isotopic analysis - technique to determine the isotopic composition of a sample (related to source and thermal maturity).

As well as meeting minimum geochemical standards, to be capable of generating hydrocarbons a source rock must have the correct thermal maturity, this is typicaly assessed using the following:

  • Vitrinite reflectance measurement
  • Spore colour index
  • Rock Eval Tmax
  • Geochemical parameters (e.g. aromatic steroids and hopanoids)

Oil and gas geochemistry

The geochemical and isotopic composition of hydrocarbons derived from gas chromatography-mass spectrometry (GC-MS) data and isotopic analysis can provide important clues to its origin (oil-source correlation) and any processes that may have affected it during migration or in the reservoir (e.g. biodegradation, water-washing, compartmentilisation).

SRK specialises in the following aspects of source rock and hydrocarbon characterisation and quality assessment:

  • Geochemical screening sampling and analysis
  • Design and execution of sampling and analysis programs
  • Detailed geochemical and stable isotopic analysis of source rock, oil and gas samples
  • Assessment of thermal maturity.
  • Assessment of reservoir compartmentilisation.
  • Oil-source correlation.
  • Integration of micro and macro scale data

Rockeval

mz-191-GC-MS-data

marcerals

lab-glassware

Contact SRK for further details of our range of source rock and hydrocarbon geochemical services for exploration.

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