Electrofacies specify reservoir rock properties, especially permeability, to simulate fluid flow in porous media. These are determined based on the classification of similar logs among different groups of logging data. Data classification is accomplished by statistical analyses such as principal component analysis, cluster analysis, and differential analysis (Amraei and Falahat 2021; Bhattacharya et al. 2016; Davis 2018; Ding et al. 2022; Kianoush et al. 2022; Kianoush et al. 2023b; Rastegarnia et al. 2016; Ye and Rabiller 2005). A model of the reservoir's geological structure is also provided to create a three-dimensional model of a reservoir's properties, in addition to estimating porosity, permeability, water saturation, and other petrophysical properties. For geological modeling, lithofacies describe rock or sedimentary units with texture, structure, mineralogy, and rock properties, and these units can be employed to match important reservoir characteristics such as permeability and porosity (Gualda and Vlach 2007; Hosseini et al. 2023; Ibrahim et al. 2016; Kadkhodaie et al. 2006; Kianoush et al. 2023a; Manshad et al. 2021).
Therefore, identifying different rock facies of reservoir rock is a fundamental task in describing the characteristics of oil reservoirs. Detection of lithofacies in the repository is complex because the type and distribution of the facies are determined by the deposition system and are affected or altered by diagenesis and tectonics (Esfandyari et al. 2023; Mathis et al. 2003; Mirkamali et al. 2016; Shakiba et al. 2015; Shoghi et al. 2020). The most common method for determining lithofacies is the use of coring. The core data directly observes the lithofacies and can accurately distinguish the different facies. However, despite all the positive features, due to the high cost of core-extraction operations and the lack of 100% recovery, this method can only be used in a small section of the field around the well (Antelo and Aguirre 2001; Heydari et al. 2012; Ismail et al. 2021; Jouini et al. 2008; Madani et al. 2019).
On the other hand, core description is time-consuming and depends on the geologist's experience. Therefore, solving this problem requires a method cheaper than coring and capable of providing precision and separation of the rock facies to a suitable size similar to that of cores without wells (Kelkar 2005; Shirneshan et al. 2018). An excellent way to respond to this need is to use well-log data. Data loggers obtain indirect information from underground data and are much cheaper than kernels. Well-log calculations can be categorized into facies or electrical facies. Log facies can display rock and reservoir fluid properties and allow users to separate sedimentary units and layers. If the lithofacies match the lithofacies, lithofacies can be substituted for lithofacies and applied. Created facies can be later used to predict rock facies in core-free or core-free intervals (Abrar 2011; Frew 2004; Kianoush et al. 2022; Kianoush et al. 2023b). A practical method for facies analysis is to create a facies classification model that splits the log data into a set of log responses that describes sediment and provides sediment separation and identification from other sediments. This set of responses is called a cluster. These clusters have introduced various methods in which there is a significant problem, namely, the dependence on the dimensionality, which is different from the geological distance and the two points that are similar in interpreting the cluster. They may not be geologically similar. The reason for this problem is the different views of geologists and loggers. This problem creates a nonlinear solid relationship between log and lithology and causes the problem of determining any partitioning of the log data into the associated sedimentary unit (Kianoush et al. 2023a; Kianoush et al. 2023b; Kianoush et al. 2023c; Lai et al. 2023; Luthi 2001).
This study addresses some of the ambiguities of using drilling cuttings and logs data in analyzing petroleum formations by combining the results of logs and describing log facies. It is mainly done by defining the log facies and the reservoir zoning of the study well.
The easy determination and application of this zoning and its reliance on log data make it possible to quickly and accurately distinguish reservoir segments from non-reservoir segments. This debate is recent in Iran, and due to past computers' inability to perform complex analyses of log facies processes, the world is also overgrowing, and the cluster analysis method is used as the principal direction analysis of the log facies identification. It is used as an essential tool for logging in advanced petroleum software. Since these facies are determined only by pure mathematical processes in the cluster analysis method and no training or fitting function is used, they are very accurate, and their application to a particular well or field is not limited. After identifying the log facies by assigning geological features to them, it can be applied to other wells on the surface of adjacent fields to match and predict the desired features (Kianoush et al. 2023a; Kolbikova et al. 2021; Rabbani et al. 2018; Roslin and Esterle 2016).
Serra and Abbott (1982), and Serra (1984) defined electric facies as "a set of responders that, in addition to characterizing the sediments, allows them to be separated." Wolf and Pelissier-Combescure (1982), and Selley (1995) introduced the first automated method for classifying "facsimiles" into electrical facies. Tavakkoli and Amini (2006) used a set of logs instead of one log to assign more features to a particular façade simultaneously. In 2015, some studies of identifying and interpreting electrical facies using the self-organized neural network (SOM) method and its prediction for sedimentary facies in the Asmari reservoir of an SW oil field of Iran have been carried out (Farazani et al. 2015; Kiaei et al. 2015; Salehi et al. 2015; Zahmatkesh et al. 2015). Kiaei et al. (2015) Modeled three-dimensional reservoir electro-physics using integrated clustering and geostatistical methods in the Persian Gulf. Their approach included hierarchical cluster analysis (HCA), Multi-resolution graph-based clustering (MRGC), and self-organized maps (SOM). Based on their results, hierarchical clustering as a robust and practical approach to data clustering was performed based on profile validation and geological information.
El Sharawy and Gaafar (2016) zoned the reservoir based on statistical analyzes in the Nubian sandstone Gulf of Suez, Egypt. They showed that the entire reservoir could be divided into at least four electro physics with significant changes in reservoir quality, which correlated with permeability changes. Tian et al. (2016) used the multi-resolution graph-based clustering (MRGC) method for determining the electrofacies (EF) and lithofacies (LF) from well-log data obtained from the intraplatform bank gas fields located in the Amu Darya Basin. Rastegarnia et al. (2016) predicted 3D flow zone index (FZI) and electrified (EFACT) volumes from a large volume of 3D seismic data. Rafik and Kamel (2017) evaluated the permeability of the Formation for a Sandstone Reservoir in the South Ramsey reservoir formations from log well data using multivariate methods. Their results showed that permeability prediction using variable selection to non-parametric alternating conditional expectations (ACE) regression is the best way to predict permeability. Kadkhodaie and Kadkhodaie (2018) reviewed different reservoir rock typing approaches from geology to seismic and dynamic and proposed an integrated rock type workflow for worldwide carbonate reservoirs. Jafarzadeh et al. (2019) investigated the distribution of reservoir facies by using the available data to identify areas that are prone to be considered in the production and development plans of the field in terms of their storage and fluid flow capacity. Eventually, the experimental results illustrated that the Adaptive multi-resolution graph-based clustering algorithm for electrifying analysis also outperformed the original MRGC method on clustering and propagation prediction with higher efficiency and stability (Kianoush et al. 2023c; mohammadinia et al. 2023; Wu et al. 2020). Recently, the electrifies predicted using the MRGC approach to generate rock mechanical properties such as Young's modulus, Poisson's ratio, unconfirmed compressive strength, and internal friction coefficient (Alameedy et al. 2023; Mahadasu and Singh 2022; Masroor et al. 2023).
Finally, Okhovvat et al. (2023) used Kernel principal component analysis (KPCA) to improve the performance of electrical facies classification.
In this study, as an innovation, the wells were zoned using well-logging diagrams, and then, by using neural network clustering methods, MRGC, and ANN, electrical facies from log data were determined.