Iranian Journal of Oil and Gas Science and Technology
Quarterly Publication

Detecting Heavy Bitumen Contaminations Using Corrected Rock-Eval Pyrolysis Data

Document Type : Research Paper

Authors

Meisam Hemmati 1
Yaser Ahmadi 2

1 MS Student, School of Geology, College of Science, University of Tehran, Tehran, Iran.

2 Assistant Professor, Chemical and Petroleum Engineering Department, Ilam University, P.O. Box 69315/516, Ilam, Iran

https://doi.org/10.22050/ijogst.2021.290550.1598
Abstract
Rock-Eval pyrolysis is a thermal method petroleum geologists use to evaluate source rock characteristics and obtain geochemistry parameters. However, there are misconceptions and misuses in exceptional cases that could lead to erroneous conclusions after using the Rock-Eval pyrolysis data to evaluate the properties of organic matter. However, a cross-plot of petroleum potential (S2) versus total organic carbon (TOC) is a useful tool for solving issues and checking the accuracy of the geochemistry parameters. The graph provides the correction criteria for the S2, hydrogen index (HI), and kerogen types. As well as the graph measures the adsorption of hydrocarbon by the mineral matrix. In addition, this article demonstrates a manner based on the data plot of S2 versus TOC to detect bitumen or hydrocarbon contaminations. Based on our knowledge about the Garau formation as a possible source rock in the petroleum geology of Iran, a geochemistry study by Rock-Eval VI pyrolysis and LECO carbon analyzer has been conducted on many rock samples collected from different outcrops in the Lurestan province, Aligudarz region, from southwest of Iran, High Zagros. Plotting the data on a cross plot of S2 versus TOC, drawing the regression line, and finding the regression equation are the best methods for determining the actual values of S2 and HI parameters and bitumen/hydrocarbon contamination. Contamination creates a y-intercept in the graph of S2 versus TOC, making geochemistry data unreliable in two study locations. The S2 and HI data unrealistically increase, while the Tmax values decline and reduce the thermal maturity of the organic matter from its actual status. The y-intercept of the graphs is removed, and the corresponding values are subtracted from the HI and S2 to skip the effect of contamination and obtain the actual geochemistry parameters. The cause of contamination in the Garau formation is the adhesion of heavy bitumen to organic facies due to the covalent bonds between carbon and hydrogen ions.

Highlights

  • Application of the petroleum potential (S2) versus total organic carbon (TOC) graph in detecting in situ bitumen contamination;
  • Evaluating the accuracy of geochemistry data obtained from the Rock-Eval pyrolysis apparatus;
  • The y-intercept in the graph of S2 versus TOC;
  • Determining depositional system tracts using the graph of S2 versus TOC.

Keywords

Rock-Eval pyrolysis
heavy bitumen contamination
geochemistry
sedimentary system tracts
Subjects
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  • Receive Date 21 June 2021
  • Revise Date 06 August 2021
  • Accept Date 20 August 2021

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