Investigating Origin, Sedimentary Environment, and Preservation of Organic Matter: A Case Study of Garau Formation

Hemmati, Meisam; Ahmadi, Yaser

doi:10.22050/ijogst.2021.291679.1601

Investigating Origin, Sedimentary Environment, and Preservation of Organic Matter: A Case Study of Garau Formation

Document Type : Research Paper

Authors

Meisam Hemmati ¹

Yaser Ahmadi ²

¹ M.S. 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.2021.291679.1601

Abstract

Knowing the characteristics of suitable environments for the precipitation of oil-prone source rocks facilitates oil explorations and leads to the development of oil fields. The current study investigates the properties of organic matter and sedimentary environment conditions of the Garau formation in various outcrop sections in Lurestan province from southwest of Iran (High Zagros) using elemental analysis, visual kerogen analysis, and Rock–Eval pyrolysis data. The geochemistry parameters indicate that the Garau formation is an excellent oil-prone source rock composed of kerogen types I and II. The oxygen index (OI) is minimal, revealing that organic matter is deposited in an anoxic sedimentary environment, suitable for preserving organic matter and hydrocarbon generation. The visual analysis of isolated kerogens from source rock samples indicates the abundance of dark amorphous organic matter (AOM) with low amounts of phytoclasts and pyrite without any palynomorph. Sedimentation appears to have occurred in deep and reduced parts of a carbonate basin during a rapid transgression. In addition, due to the effect of thermal maturation, the color of amorphous organic matter has darkened. The elemental analysis and van Krevelen diagram are employed to show the type of organic matter and reveal that the thermal maturity is related to the oil window. Elemental analysis reveals the high content of organic sulfur in the structure of kerogen. Moreover, the content of pyritic sulfur (Sp) and organic sulfur (So) is calculated.

Highlights

Quality and quantity of the organic matter in the Garau formation according to pyrolysis and elemental analysis;
The organic facies assessment using geochemistry parameters;
The visual kerogen analysis and palynology.

Keywords

Elemental analysis

Garau formation

Sedimentary environment

Visual kerogen analysis

Subjects

Petroleum Engineering

Alavi, M., Structures of The Zagros Fold-thrust Belt in Iran, American Journal of Science, Vol. 307, No. 9, p. 1064–1095, 2007.

Arthur, M. A., Brumsack, H. J., Jenkyns, H. C., and Schlanger, S. O., Stratigraphy, Geochemistry, and Paleoceanography of Organic Carbon-rich Cretaceous Sequences, in Cretaceous Resources, Events, and Rhythms, Springer, Dordrecht, p. 75–119, 1990.

Arthur, M. A., Dean, W. E., and Schlanger, S. O., Variations in The Global Carbon Cycle During the Cretaceous Related to Climate, Volcanism, and Changes in Atmospheric CO2, The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to Present, Vol. 32, p. 504–529, 1985.

Batten, D. J., Jansonius, J., and Mcgregor, D. C., Palynofacies, Palynology: Principles and Applications, Vol. 3, p. 1011–1084, 1996.

Baudin, F., A Late Hauterivian Short-Lived Anoxic Event in The Mediterranean Tethys: The “Faraoni Event”, Comptes Rendus Geosciences, Vol. 337, No. 16, p. 1532–1540, 2005.

Behar, F., Beaumont, V., and Penteado, H. D. B., Rock–Eval 6 Technology: Performances and Developments, Oil & Gas Science and Technology, Vol. 56, No. 2, p. 111–134, 2001.

Bernard, B. B., Bernard, H., and Brooks, J. M., Determination of Total Carbon, Total Organic Carbon and Inorganic Carbon in Sediments, College Station, Texas, p. 1–5, 2010.

Berner, R. A. and Raiswell, R., Burial of Organic Carbon and Pyrite Sulfur in Sediments Over Phanerozoic Time: A New Theory, Geochimica Et Cosmochimica Acta, Vol. 47, No. 5, p. 855–862, 1983.

Bordenave, M. L. and Burwood, R., Source Rock Distribution and Maturation in The Zagros Orogenic Belt: Provenance of The Asmari and Bangestan Reservoir Oil Accumulations, Organic Geochemistry, Vol. 16, No. 1, p. 369–387, 1990.

Bordenave, M. L. and Hegre, J. A., Current Distribution of Oil and Gas Fields in The Zagros Fold Belt of Iran 424 and Contiguous Offshore as The Result of The Petroleum Systems, Geological Society, London, Special Publications, Vol. 330, No. 1, p. 291–353, 2010.

Brooks, J., Cornford, C., and Archer, R., The Role of Hydrocarbon Source Rocks in Petroleum Exploration, Geological Society, London, Special Publications, Vol. 26, No. 1, p. 17–46, 1987.

Calvert, S. E. and Karlin, R. E., Relationships Between Sulphur, Organic Carbon, And Iron in The Modern Sediments of The Black Sea, Geochimica Et Cosmochimica Acta, Vol. 55, No. 9, p. 2483–2490, 1991.

England, W. A., Reservoir Geochemistry-A Reservoir Engineering Perspective, Journal of Petroleum Science and Engineering, Vol. 58, No. 3–4, p. 344–354, 2007.

Ezampanah, Y., Sadeghi, A., Jamali, A. M., and Adabi, M. H., Biostratigraphy of The Garau Formation (Berriasian? Lower Cenomanian) In Central Part of Lurestan Zone, Northwest of Zagros, Iran, Cretaceous Research, Vol. 46, p. 101–113, 2013.

Farzipour‐Saein, A., Yassaghi, A., Sherkati, S., and Koyi, H., Basin Evolution of The Lurestan Region in The Zagros Fold‐And‐Thrust Belt, Iran, Journal of Petroleum Geology, Vol. 32, No. 1, P. 5–19, 2009.

Haq, B. U., Hardenbol, J. A. N., and Vail, P. R., Chronology of Fluctuating Sea Levels Since the Triassic, Science, Vol. 235, No. 4793, P. 1156–1167, 1987.

Hsu, C. S. and Robinson, P. R., Practical Advances in Petroleum Processing, Springer, New York, Vol. 1, p. 79–101, 2006.

Hunt, J. M., Petroleum Geochemistry and Geology, 2nd Edition, W. H. Freeman and Company, New York, p. 743, 1996.

Jackson, K. S., Hawkins, P. J., and Bennett, A. J. R., Regional Facies and Geochemical Evaluation of The Southern Denison Trough, Queensland, The APPEA Journal, Vol. 20, No. 1, p. 143–158, 1985.

Jones, R. W., Organic Facies, In Advances in Petroleum Geochemistry, Brooks, J. and Welte, D. (Eds.), Academic Press, London, Vol. 2, p. 1–90, 1987.

Kobraei, M., Rabbani, A. R., and Taati, F., Source Rock Characteristics of The Early Cretaceous Garau and Gadvan Formations in The Western Zagros Basin-southwest Iran, Journal of Petroleum Exploration and Production Technology, Vol. 7, No. 4, p. 1051–1070, 2017.

Leckie, R. M., Bralower, T. J., and Cashman, R., Oceanic Anoxic Events and Plankton Evolution: Biotic Response to Tectonic Forcing During the Mid‐Cretaceous, Paleoceanography, Vol. 17, No. 3, p. 13–1, 2002.

Lewan, M. D., Sulphur-Radical Control on Petroleum Formation Rates, Nature, Vol. 391, No. 6663, p. 164–166, 1998.

Mahbobipour, H., Kamali, M. R., and Solgi, A., Organic Geochemistry and Petroleum Potential of Early Cretaceous Garau Formation in Central Part of Lurestan Zone, Northwest of Zagros, Iran, Marine and Petroleum Geology, Vol. 77, p. 991–1009, 2016.