Optimization of Petrophysical Evaluation Utilizing Variable Cementation Factor for Identification of Pay-Zones in a Field within Zagros Bain

Document Type : Original Article

Authors
Koorosh Keramati 1
Ahmad Reza Rabbani 2
Khaled Maroufi 3
Ali Kadkhodaie 4
1 M.Sc. Student, Department of Petroleum Engineering, Faculty of Petroleum and Geoenergy Engineering, Amirkabir University of Technology, Tehran, Iran
2 Professor, Department of Petroleum Engineering, Faculty of Petroleum and Geoenergy Engineering, Amirkabir University of Technology, Tehran, Iran
3 Assistant Professor, Faculty of Petroleum and Natural Gas Engineering, Tabriz University of Technology, Tabriz, Iran
4 Professor, Earth Sciences Department, Agriculture Faculty, Tabriz University, Tabriz, Iran
Abstract
Identification of hydrocarbon-bearing zones, as a primary objective of exploration and production projects, requires precise analysis of petrophysical data. Cementation factor is one of the key parameters in petrophysical evaluation, which is used to calculate water saturation (such as the Archie and Indonesia equations). This coefficient describes the degree of cementation and consolidation on porosity. For carbonate rocks, cementation factor depends on pore type. Minor variations in this factor can influence fluid saturation estimates, thereby posing challenges for accurate identification of pay-zones. This study aims to investigate the effect of employing variable cementation exponent values instead of fixed ones on petrophysical analysis results using Geolog software (Multimin modeling). Effective porosity data resulted from the software were applied into the Borai equation (1987) and variable and depth-dependent cementation exponent values were calculated. They were then compared to the commonly used constant values. The results demonstrated evident differences between water saturation values obtained from two methods ranging from 1% to 9%. Accordingly, pay-zone thickness and oil-water contact location varied. Comparison of the identified pay-zones revealed higher accuracy of the variable cementation exponent-based model. The main pay-zone of the studied well is within units 3 and 4 of the Sarvak formation, exhibiting favorable porosity and hydrocarbon saturation. Ultimately, the findings of this study revealed that the precise determination of fluid saturation values, based on the variable cementation exponent, facilitates more accurate identification of reservoir zones and fluid contact surfaces, thereby minimizing errors in volumetric estimations.

Keywords

Subjects

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  • Receive Date 08 July 2025
  • Revise Date 27 September 2025
  • Accept Date 17 October 2025