Geomechanics and Geoenergy Journal

Geomechanics and Geoenergy Journal

Application of Shannon Entropy in Quantifying Geological Heterogeneity, Porosity, and Permeability: A Case Study of the Kangan Formation in the Central Persian Gulf

Document Type : Original Article

Authors
Vahid Tavakoli 1
Mehdi Nokhstin Mortazavi 2
1 School of Geology, College of Science, University of Tehran, Tehran, Iran
2 M.Sc. in Geophysics, Academic Center for Education, Culture and Research (ACECR)
10.22107/ggj.2026.579708.1261
Abstract
This study aims to apply Shannon entropy to analyze and compare facies and petrophysical heterogeneity in the K1 and K2 units of the Kangan Formation. Facies were first classified into twelve groups based on petrographic studies, and facies entropy was calculated from their relative frequencies. Subsequently, core porosity and permeability were categorized into value classes, and Shannon entropy was computed independently for each parameter. Diagenetic features were also examined to interpret data distribution patterns. The results demonstrate that Shannon entropy can quantitatively express structural differences between the two units. While facies entropy values are similar in both units, their facies distribution patterns differ. Porosity entropy in K2 is 1.58 compared to 1.12 in K1, indicating a wider porosity distribution in K2. Permeability entropy values are 1.95 in K2 and 1.60 in K1, reflecting greater diversity in permeability classes within K2. The higher porosity and permeability entropy in the K2 unit is consistent with its diagenetic characteristics, where intergranular and intragranular dissolution has created or expanded secondary pore spaces, distributing porosity and permeability values across multiple classes. In contrast, more extensive microcrystalline dolomitization, cementation, and particularly anhydrite cementation in K1 have resulted in pore filling or throat tightening, concentrating data in low-permeability and low-porosity classes. Thus, porosity-reducing diagenetic processes in K1 yield lower entropy, while porosity-enhancing or pore-preserving processes in K2 produce higher entropy. This relationship indicates that Shannon entropy can effectively reflect the differentiating effects of various diagenetic styles through a quantitative index. Based on these findings, Shannon entropy provides a simple, reliable, and appropriate approach for assessing heterogeneity in carbonate reservoirs and can serve as a valuable complement to conventional petrophysical and sedimentological methods for analyzing reservoir units and modeling reservoir behavior.
Keywords
Shannon
Entropy
Reservoir Heterogeneity
Kangan Formation
Persian Gulf
Petrophysics
Diagenesis
[1] Ahr, W. M. (2008). Geology of carbonate reservoirs:
the identification, description and characterization of
hydrocarbon reservoirs in carbonate rocks. John Wiley &
Sons.
[2] Asgari, A., Kadkhodaie, A., & Rahimpour-Bonab, H.
(2024). Sequence stratigraphy, diagenesis and geological
zonation of the lower Triassic carbonate reservoir of the
Kangan formation from the central to Northern Persian
Gulf. Carbonates and Evaporites, 39(3), 85.
https://doi.org/10.1007/s13146-024-00972-3
[3] Mohammadi, M., Kadkhodaie, A., Rahimpour-Bonab,
H., Kadkhodaie, R., & Aleali, M. (2024). Stratigraphic
framework and diagenetic features related to reservoir
quality of the triassic carbonates in central to northern
Persian Gulf. Carbonates and Evaporites, 39(2).
https://doi.org/10.1007/s13146-024-00972-3
[4] Tavakoli, V. (2020). Carbonate Reservoir
Heterogeneity: Overcoming the Challenges. Springer.
[5] Fakhar, M., Rezaee, P., & Karimian Torghabeh, A.
(2024). Investigating the reservoir quality of the Early
Triassic succession with a new perspective on diagenesis
and sequence stratigraphy in the center of the Persian
Gulf, South Pars. Geoenergy Science and Engineering,
232, 212367-212391.
6] فخار، م.، رضایی، پ.، و کریمیان طرقی، ا. ) 1402 (. بررس ی ]
کیفیت مخزنی توالی تریاس پیشین با نگاهی نو بر فراینده ا ی
دیاژنزی و چین هنگاری سکانسی در مرکز خلیج فارس، پارس
.212391-212367 , جنوبی. علوم و مهندسی نفت, 232
[7] Rahimpour-Bonab, H., Esrafili-Dizaji, B., & Tavakoli,
V. (2010). Dolomitization and anhydrite precipitation in
Permo-Triassic carbonates at the South Pars gas field,
offshore Iran: controls on reservoir quality. Journal of
Petroleum Geology, 33(1), 43-66.
https://doi.org/10.1111/j.1747-5457.2010.00463.x
[8] Moradi, M., Kadkhodaie, A., Rahimpour-Bonab, H.,
& Kadkhodaie, R. (2024). Integrated reservoir
characterization of the Permo-Triassic gas reservoirs in
the Central Persian Gulf. Petroleum, 10(4), 594-607.
https://doi.org/10.1016/j.petlm.2024.03.005
[9] Shannon, C. E. (1948). A mathematical theory of
communication. The Bell System Technical Journal,
27(3), 379-423.
[10] Silva, L.C.V. et al. (2025). Entropy-based measure
of rock sample heterogeneity derived from micro-CT
images. Journal of Petroleum Science and Engineering,
215, 110123.
https://doi.org/10.1016/j.petrol.2022.110123
[11 ] طهماسبی، م.، و مسیحی، م. (1393). مقاله رتبه‌بندی تحقق‌های مدل مخزن بر اساس روش آنتروپی. کنفرانس بین‌المللی مهندسی نفت.
عمرانی، س.، و توکلی، و. (1403). بررسی عوامل کلیدی مؤثر بر دقت محاسبات اشباع آب در مخازن کربناته: سازندهای کنگان و دالان، غرب خلیج فارس. نشریه ژئومکانیک نفت، 12(3)، 45-60[12 ]
[13] Tavakoli, V., & Jamalian, A. (2019). Porosity
evolution in dolomitized Permian–Triassic strata of the
Persian Gulf: Insights into the porosity origin of dolomite
reservoirs. Journal of Petroleum Science and Engineering,
181, 106191.
https://doi.org/10.1016/j.petrol.2019.106191
Geomechanics and Geoenergy Journal
Volume 8, Issue 2
Summer 2025
Pages 80-93