Addressing Structural Complexity in Asmari Fractured Reservoirs with Borehole Imaging Technique and VSP

Background and Objective: Exploration of carbonate reservoirs in structurally complex areas, particularly those overlain by extensive evaporate formations, poses significant challenges in structural delineation. Lack of adequate structural geology information, especially in naturally fractured reservoirs, hampers drilling operations. In Iran, insufficient data on fractured reservoirs have hindered drilling activities. This study aims to assess the impact of limited structural information on drilling operations in complex naturally fractured reservoirs and underscores the efficacy of borehole imaging tools in addressing these challenges. The primary objective is to establish a precise structural model for the Asmari reservoir in the Gachsaran field. Materials and Methods: Utilizing well site geologist reports and formation cuttings analysis, this research examines drilling challenges encountered in penetrating the lower Asmari reservoir. Oil-Based Mud Micro Imager-Ultrasonic Borehole Imager (OBMI-UBI) tools were deployed in the interval from 2117 to 2772 m to investigate discrepancies in predicted reservoir depths. Results: The analysis revealed a deviation in the well trajectory, with an initial northeast (NE) direction shifting gradually to southwest (SW) until reaching total depth (TD). Caprock and bedding dips plotted alongside the trajectory unveiled parallelism with the middle Asmari layers, indicating the need for a directional change to exit the reservoir successfully. Borehole imaging played a pivotal role in delineating structural complexities, providing crucial insights for the effective positioning of wells. Conclusion: Insufficient structural data in complex carbonate reservoirs pose significant challenges to drilling operations. However, the deployment of borehole imaging tools, as demonstrated in this study, enables precise structural modeling and enhances drilling efficiency in such environments.