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This document is an editorial for a special issue of the journal Minerals, focusing on the heterogeneities of carbonate reservoirs. The editorial emphasizes the importance of understanding these heterogeneities for optimizing exploration and production strategies, as they influence fluid flow behavior and the recoverable reserves within the reservoir. The editorial also highlights the need for further research to explore the implications of heterogeneities at a broader scale and recommends the use of advanced technologies and multidisciplinary approaches. The document provides a summary of five papers included in the special issue, which cover topics such as the genetic mechanism of dolomite reservoirs, diagenetic alterations in the Chiltan Formation, the formation mechanism of dolomite-mottled limestone reservoirs, characteristics of crystalline dolomites in the Sanshanzi Formation, and facies variations in the Sarvak Formation. The research presented in this special issue contributes to our understanding of ancient carbonate platforms and dolomite reservoirs and provides a framework for future studies in oil and gas exploration. [Extracted from the article]

This document is an editorial for a special issue of the Minerals journal focused on the deposition, diagenesis, and geochemistry of carbonate sequences. The editorial highlights the importance of studying carbonate formations, which serve as archives of past climates, tectonic events, and biological evolution. It emphasizes the significance of understanding depositional characteristics, diagenetic alterations, and geochemical variations within carbonate sequences for unraveling their geological significance and economic potential. The editorial invites readers to explore the collection of articles in the special issue, which cover diverse topics and methodologies, and contribute to our understanding of carbonate systems worldwide. [Extracted from the article]

Heterogeneity analysis in carbonate reservoirs is of great importance for the interpretation of their characteristics. This study focuses on the evaluation of pore‐type heterogeneity by means of the sonic wave velocities in the carbonate–evaporite series of Permian–Triassic sequences in the Persian Gulf. Thin section petrography and laboratory measured the porosity and permeability of 1576 samples, as well as routine wire‐line logs, were employed. To manage heterogeneity, six electrofacies (EF) were determined based on an integrated analysis of compressional, shear and Stoneley waves as well as three routine logs (gamma, neutron and density). The frequency of pore types in each electrofacies was calculated. Then, the heterogeneity of pore‐type distribution in each electrofacies was measured by standard error and coefficient of variation. Sonic velocity has been compared with the geological properties of electrofacies. Results indicated that velocity is affected by factors other than the amount of porosity, facies or lithology. The standard error values in all electrofacies were close to zero. The coefficient of variation values ranges from 1.08 to 4.60. The lowest amount of coefficient of variation was observed in EF6 in the Khuff (K) 4 zone for moldic porosity. This value for intercrystalline porosity distribution in EF1 in the K1 zone was low, too. These results indicate the lowest standard deviation and the highest homogeneity in the distribution of intercrystalline and moldic porosities in K1 and K4. Also, comparing the mean values of sonic logs in each electrofacies with the total mean value in the whole sequence indicated that there is a relationship between sonic velocity logs and the type of porosity. High values of sonic velocity correspond to intercrystalline porosity in K1 and low values of velocity correspond to moldic porosity in K4. Results show that integrated pore‐type studies should be carried out to understand the sonic velocities in carbonate reservoir rocks. [ABSTRACT FROM AUTHOR]

Abstract The porous network controls the behavior of fluids in the reservoir rocks. In carbonate reservoirs fluid flow characteristics do not certainly follow initial sedimentary fabrics. Therefore in these reservoirs, the properties of the porous network should be used in determining the facies. In this study, using a combination of petrographic, reservoir petrophysical and reservoir engineering data, porous network in Aptian-Albian Dariyan carbonates have been studied in one of the central Persian Gulf fields. Accordingly, four pore facies were determined by capillary pressure curves from mercury injection and nuclear magnetic resonance data in four different types of lithology with different microfacies. Also, 13 different petrophysical parameters of these curves derived from both methods and compared with each other. A clear trend was observed in reducing the reservoir quality from pore facies 1 to pore facies 4. The performance of the capillary pressure curves obtained from mercury injection and nuclear magnetic resonance and their derived parameters in 4 facies and the effect of lithology on these curves have been investigated. Results showed that the porosity of the NMR is completely independent of lithology and complexity of the porous system, while the permeability-dependent parameters are largely influenced by both lithology and pore system structure. It was also shown that the NMR curves are a suitable tool for determining the pore facies and their petrophysical parameters in homogeneous tight carbonate lithology with a simple porous system. Graphical abstract Image 1 Highlights • NMR derived porosity, permeability and pore-throat size is presented in Aptian-Albian Dariyan carbonate reservoir. • Pseudo-capillary curves calculated from NMR data and compared with MICP results. • Various parameters extracted from pseudo-capillary curves and compared with MICP results. • Microfacies defined in the reservoir and compared with NMR pore facies. • Results showed that heterogeneity in lithology is the main controlling factor on the final results. [ABSTRACT FROM AUTHOR]

Abstract Calculating hydrocarbon in place is one of the most important aspects to be considered in reservoir evaluation. Carbonate rocks with high heterogeneity, exhibit significant changes in petrophysical and lithological properties. Archie's exponents (m and a) are basic parameters for saturation calculations. Uncertainties in obtaining these exponents lead to considerable errors in the saturation assessment. In this study, various pore and rock typing methods were carried out on a Permian–Triassic carbonate reservoir in the central Persian Gulf, Iran. The used methods include pore typing, pore facies classification, velocity deviation log, reservoir quality index, Winland R35, Pittman R35 and ranges of core permeability. Archie's exponents were obtained for different classes based on extracted data from petrographical studies, conventional core analysis and wire line log data. Results showed that determination of rock types based on pore typing has the greatest effect on the precise determination of Archie's exponents. On the other hand, the most unreliable results were related to the velocity deviation log. Pore types directly control the connectivity of the fluid pathways and so have the most important effect. Combining pore types in various groups such as velocity deviation or pore facies classification, reduce the measurement accuracy of Archie's exponents and resulted water saturation. Finally, it can be concluded that, in addition to the high impact of pore type on the accuracy of the obtained exponents, the permeability and pore throat radius are less effective in determining the Archie's exponents. Graphical abstract Image 1 Highlights • Archie's exponents in Kangan and Dalan formations in Iran considered for the first time. • Various rock and pore typing methods used for considering the effect of heterogeneity. • Pore typing is the best method for classifying the reservoir rocks according to their m and a exponents. • Increasing heterogeneity decrease the accuracy of water saturation calculation in carbonate reservoirs. • Reducing accuracy from pore type to pore facies and velocity-deviation log demonstrate the effect of heterogeneity. [ABSTRACT FROM AUTHOR]