3D geological modeling and reservoir production numerical simulation of multiple scenarios in fractured-karstified carbonate reservoirs using high-resolution outcrop characterization

Abstract

This study presents a multidisciplinary workflow to improve understanding of fractured and karstified carbonate reservoirs. The study seeks to uncover geological mechanisms behind fracturing and karstification by integrating analog outcrop fieldwork with regional correlation. This knowledge is crucial for building more accurate geological models and improving the management of these complex reservoirs. We use the Jandaíra Formation in the Potiguar Basin, Brazil, as an analog for fractured and karstified carbonate reservoirs. Our results focus on the Furna Feia cave, characterized by dissolution dome structures and NW-SE-trending conduits. The regional stratigraphic analysis identified lithofacies patterns and correlated system tract cycles to map the most karstified layers, relating cave formation to a regional SB-2 unconformity. Structural analysis revealed that rift faults, caves, and fractures are oriented NW-SE and NE-SW. The 3D regional geological model covers an area measuring 30 km in length and 14 km in width, extending vertically about 150 m. It integrates data from wells, structural mapping, fracture model, and karst features, revealing intensely dissolved layers between two unconformities named SB-1 and SB-2. Based on this, we propose a new approach to karst modeling that combines conduits and karstified fractures following a comprehensive reservoir-scale conceptual model. As a result, four scenarios were simulated to evaluate the water and oil production history, similar to analogous carbonate reservoirs. We conclude that including karst and fractures improves performance and increases production but affects some wells due to premature water breakthroughs. Therefore, effective management and optimized planning for wells are essential for reservoirs containing karst and fractures. This multidisciplinary workflow, which creates geological models and evolves to reservoir production numerical simulation, assesses different scenarios and provides insights into potential outcomes and associated risks that influence decision-making in production development projects.