Iranian Journal of Oil and Gas Science and Technology
Quarterly Publication

Hydrocarbon Generation Potential and Paleo-Depositional Environments of the Laffan Formation in the Binak Oilfield: Results from Rock-Eval Pyrolysis and Organic Petrographic Studies

Document Type : Research Paper

Authors

Bahram Alizadeh 1
Zollfaghar Eivazi Nezhad 2
Majid Alipour 3

1 Professor, Department of Petroleum Geology and Sedimentary Basins, Faculty of Earth Sciences, Shahid Chamran University of Ahvaz, Ahvaz, Iran

2 M.S. Student, Department of Petroleum Geology and Sedimentary Basins, Faculty of Earth Sciences, Shahid Chamran University of Ahvaz, Ahvaz, Iran

3 Assistant Professor, Department of Petroleum Geology and Sedimentary Basins, Faculty of Earth Sciences, Shahid Chamran University of Ahvaz, Ahvaz, Iran

https://doi.org/10.22050/ijogst.2022.336808.1635
Abstract
In this study, the hydrocarbon potential and depositional environments of the Coniacian Laffan formation were investigated in the Binak oilfield, SW Iran. With an average thickness of 80 m, the Laffan formation consists mainly of gray shales and thin argillaceous limestones in the study area. In order to investigate the hydrocarbon potential, 22 cutting samples from 5 wells of the Binak oilfield were analyzed by Rock-Eval 6 pyrolysis and organic petrographic techniques. The hydrogen index (HI) versus Tmax diagrams indicated mixed-type II/III kerogen with a maturity corresponding to the early stages of the oil window (Tmax ≈ 435 °C). In addition, plots of S1+ S2 versus TOC were consistent with a weak to excellent hydrocarbon potential for the Laffan formation. On the other hand, organic petrographic techniques indicated that the primary organic constituents of the Laffan formation are inertinite and bituminite with subordinate amounts of amorphous organic matter (AOM). In other words, the contained organic matter was mainly composed of inertinite and lacked significant hydrocarbon potential. An abundance of inertinite and the conspicuous absence of vitrinite macerals in the studied samples suggested that the Laffan formation was deposited under sub-oxic marine conditions. Furthermore, the presence of bituminite in the studied samples greatly influenced the Rock-Eval pyrolysis readings, so geochemical evaluation of the Laffan formation using only Rock-Eval pyrolysis data may lead to erroneous interpretations. Therefore, a combination of Rock-Eval and organic petrographic methods is necessary for reliable geochemical evaluation of the Laffan formation. The results of this study can be useful for a better understanding of the Cretaceous hydrocarbon system in the study area.

Highlights

  • Rock-Eval pyrolysis results indicate kerogen type II/III in the Laffan formation;
  • Organic petrographic studies indicate that inertinites are predominant macerals;
  • The presence of bituminite has influenced the Rock-Eval pyrolysis interpretations;
  • Pyrolysis data should be combined with organic petrographic observations.

Keywords

Laffan formation
Source rock evaluation
Rock-Eval 6 pyrolysis
Organic petrography
Vitrinite reflectance
Binak Oilfield
Subjects
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  • Receive Date 09 April 2022
  • Revise Date 15 June 2022
  • Accept Date 19 July 2022

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