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Source Rock Analyzer (SRA)

Overview

Thumbnail image of Source Rock Analyzer Pyrolysis analysis of geologic samples provides information about thermal maturation, source of hydrocarbons and petroleum potential. Analysis is performed on dried and powdered samples and results may not be reliable in samples with low organic carbon content, high carbonate content, or samples containing an abundance of immature organic matter.

Instrument Make and Model

Weatherford Source Rock Analyzer

Estimated Measurement Time

  • Sample Preparation: 2 minutes–several days
  • Sample Measurement: 1 sample/hour

Quantity of Sample Material

10–100 mg per sample

Principles & Analytical Capabilities

The Source Rock Analyzer (SRA) makes use of a flame ionization detector (FID), CO detector, and CO2 detector to obtain the parameters below. The pyrolysis stage uses helium as a carrier gas with an active FID. The FID is primarily used to measure S1 (free hydrocarbons), S2 (hydrocarbon potential), and Tmax (maximum rate of hydrocation generation). All other parameters are obtained from the CO and CO2 detectors or are calculated using measurements from all detectors.

S1 is an indication of free hydrocarbons already generated and present in the sample. Hydrocarbons that vaporize at temperatures up to ~330°C are included in S1. Hydrocarbons that vaporize at higher temperatures are included in S2.

S2 is an indication of hydrocarbon potential and represents the quantity of hydrocarbons that a sample has the potential of producing should maturation continue. It consists of hydrocarbons released from the cracking of kerogen and high molecular weight hydrocarbons that do not vaporize for S1.

S3 is an indication of the amount of oxygen in the kerogen and is used to calculate the oxygen index (OI). It is a measure of organic CO2 evolved during low temperature (<390°C) pyrolysis.

S4 is an indication of residual organic carbon remaining after pyrolysis and released during oxidation. It is measured by a combination of the evolved CO and CO2.

Tmax is the temperature at which the maximum rate of hydrocation generation (S2) occurs. It is the primary indication of thermal maturity.

Total organic carbon (TOC) is the wt% organic carbon of the sample and is the sum of pyrolyzed carbon released during pyrolysis (S1 and S2) and residual carbon released during oxidation (S4).

Hydrogen index (HI) represents the amount of hydrogen relative to the TOC in a sample. It is an indicator of the kerogen type and its potential to generate oil or gas.

Oxygen index (OI) represents the amount of organic oxygen relative to the TOC. It is used to help identify the source of organic matter and distinguish between marine and terrestrial organic matter.

Production index (PI), or transformation ratio, indicates the amount of free hydrocarbons (S1) relative to the total amount of hydrocarbons a rock can potentially produce (S1 and S2). Used in determining thermal maturity and typically increases with depth.

Data Generated

Data components:

  • S1
  • S2
  • S3
  • S4
  • Tmax
  • TOC
  • HI (hydrogen index)
  • OI (oxygen index)
  • PI (production index)

Data files:

  • Results (CSV): tabular file of reduced measurement data

Raw files:

  • Pyrogram (CSV): tabular file of chromatogram and acquisition results

Data Example

Graph of oxygen and hydrogen indexes in relation to the three kerogen types from Hole U1545A of IODP Expedition 385 in the Guaymas Basin.
Oxygen and hydrogen indexes in relation to the three kerogen types from Hole U1545A of IODP Expedition 385 in the Guaymas Basin.1, 2

Procedures & Manuals

References

1  Teske, A. P., Lizarralde, D., Höfig, T. W., Aiello, I. W., Ash, J. L., Bojanova, D. P., Buatier, M. D., Edgcomb, V. P., Galerne, C. Y., Gontharet, S., Heuer, V. B., Jiang, S., Kars, M. A. C., Kim, J.-H., Koornneef, L. M. T., Marsaglia, K. M., Meyer, N. R., Morono, Y., Negrete-Aranda, R., … Zhuang, G. (2021). IODP Expedition 385 Source rock analyzer (SRA) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.7846641

2  Teske, A., Lizarralde, D., Höfig, T.W., Aiello, I.W., Ash, J.L., Bojanova, D.P., Buatier, M.D., Edgcomb, V.P., Galerne, C.Y., Gontharet, S., Heuer, V.B., Jiang, S., Kars, M.A.C., Khogenkumar Singh, S., Kim, J.-H., Koornneef, L.M.T., Marsaglia, K.M., Meyer, N.R., Morono, Y., Negrete-Aranda, R., Neumann, F., Pastor, L.C., Peña-Salinas, M.E., Pérez Cruz, L.L., Ran, L., Riboulleau, A., Sarao, J.A., Schubert, F., Stock, J.M., Toffin, L.M.A.A., Xie, W., Yamanaka, T., and Zhuang, G., 2021. Site U1545. In Teske, A., Lizarralde, D., Höfig, T.W., and the Expedition 385 Scientists, Guaymas Basin Tectonics and Biosphere. Proceedings of the International Ocean Discovery Program, 385: College Station, TX (International Ocean Discovery Program). https://doi.org/10.14379/iodp.proc.385.103.2021