زون‌بندی مخزنی بر اساس داده‌های پتروگرافی و پتروفیزیکی (مطالعه موردی: بخش بالایی سازند سروک در یکی از میدان‌های نفتی ناحیه دشت آبادان، جنوب غربی ایران)

Abstract

Summary In this study, results of microscopic studies on thin sections, core porosity data, and petrophysical charts along a well were used to evaluate the reservoir quality of the upper part of the Sarvak Formation in one of the oil fields in Abadan Plain. This research showed that SMLP-based zonation can be applied on a field scale as it could appropriately represent the heterogeneity of the Sarvak reservoir at a large scale. Introduction The main purpose of the study is to investigate the reservoir quality of the upper part of Sarvak Formation in an oilfield within Abadan Plain by analyzing the facies and sedimentary environment, pore system, diagenetic processes, electrofacies, and flow units. To this end, a set of microscopic thin section data, core porosity data, and well logs were employed as input data. The main advantages of the proposed methodology include its ability to predict and justify changes in reservoir quality, its contribution to reservoir modeling and reservoir zonation, and the resultant reduction of the drilling cost in the studied oilfield. Methodology and Approaches The set of input data used in this study included 269 m of drilling cores, 694 thin sections prepared from the cores, porosity-permeability data from 548 core plug samples, and petrophysical logs including gamma, neutron, sonic, density, and resistivity reading at a key well in an oilfield within Abadan Plain, southwestern Iran. Results of petrographic studies (i.e., sedimentary texture, facies belts, diagenetic processes, and pore systems) and electrofacies were incorporated into a framework for identifying the zones introduced by SMLP, and the relationship between them was examined and interpreted. Results and Conclusions Based on the microscopic studies, it was found that the formation was composed of 5 facies belts, namely tidal flat zone, lagoon, shoal, middle ramp, and outer ramp facies were deposited. Dissolution, fracturing, cementation, compaction, and dolomitization were identified as the most important diagenetic processes affecting the reservoir quality in Sarvak Formation. Electrofacies (EF) were determined based on well charts and hierarchical clustering analysis. Using two petrophysical methods, namely, flow zone index (FZI) and stratigraphic modified Lorenz plot (SMLP), we ended up detecting 5 and 7 flow units, respectively. Finally, microscopic analysis of thin sections and investigation of electrofacies and hydraulic flow units in the framework of reservoir zonation by using the SMLP were devised to review the zonations and interpret them appropriately. As a result, the grain-supported facies related to the shoal and the middle ramp environments and the diagenetic processes enhancing the reservoir quality (e.g., dissolution and fracturing) were found to lead to the best-reservoir quality zones. On the other hand, the poor reservoir quality zones were found to be a result of the mud-supported facies of the middle and outer ramp, tidal flat, and lagoon environments, and adverse diagenetic processes such as cementation, compaction, and dolomitization. Results of this study showed that reservoir zonation using the SMLP can be of help in the interpretation of reservoir heterogeneities in the upper part of the Sarvak Formation at the field scale.