Fractures and Geological Analysis of the Water Breakthrough Patterns for the Production in X Carbonate Reservoir: A Case Study from Southeast Iraq

This study examines fracture analysis and characterization of the X carbonate reservoir within the AG oilfield in southeast Iraq, near the Iraq-Iran border. The reservoir is categorized into zones A, B, and C, each presenting unique challenges due to its complex fractured-porous nature, limited conventional log responses, a lack of special logs, and the structural difficulties caused by the Zagros orogeny. To evaluate fracture geometry and distribution and water breakthrough patterns and their influence on reservoir quality and production efficiency, the core samples, well logs, and thin sections from 10 wells were studied. The X carbonate reservoir analysis indicated that fractures typically range from 1–25 cm in length and 0.02–0.08 mm in width, predominantly high-angle to near-vertical fractures enhancing the reservoir's permeability. The reservoir properties indicate that member B has better physical properties than member A, with higher porosity and permeability. Fracture density varies significantly across the reservoir zones, ranging between 0.7 and 9.6 fractures/meter, averaging 4.7 fractures/meter and decreasing from A to C. In zones A and B, especially in the dolomite and limestone lithologies, these fractures contribute to improved permeability and higher well productivity. For example, wells AG-7A and AG-16 maintain steady production rates of 5000 and 3000 barrels per day. However, these fractures also lead to water breakthroughs, with 57.9% of wells encountering increasing in water cuts above 10%, therefore highlighting the difficulty in managing water production. Additionally, the time for water breakthrough and the location and perforation of every well were also considered in the process of water breakthrough analysis. Furthermore, the study identified three primary mechanisms for water breakthrough: gradual edge water invasion in member B of the southern area, fractures causing water breakthrough from member B to A, and bottom water invasion in the northern area. These findings highlight fractures' essential role in encouraging oil extraction and fasting water breakthroughs, which requires effective reservoir management to maximize hydrocarbon recovery while limiting water production.