Comprehensive analysis of stress magnitude and orientations and natural fractures in complex structural regimes oil reservoir: Implications for tectonic and oil field development in the Zagros suture zone

Abstract

Complex structures with different stress regimes pose challenges in tectonic studies and have implications for the oil and gas industry. The analysis of in-situ stress state and natural fractures in the Dezful Embayment, the southwestern part of the Zagros fold and thrust belt (ZFTB) in Iran, and their implications for tectonic and oil field development are poorly understood. This study analyzes stress orientations, natural fractures, pore pressure (Pp), and stress regime in two oil fields located in the Zagros foothills. The study utilized various data types, including image logs and conventional logs, to determine the in-situ stresses and their implications for energy field development. The results show that the mean orientations of the maximum horizontal stress SH in Field A and Field B are N32°E and N55°E, respectively. The analysis of natural fractures indicates that most tensional fractures are subparallel to the orientation of the maximum horizontal stresses, and the present stress state is responsible for these fractures. The analysis of stress magnitudes demonstrates that the stress regime in Field A changes from thrust faulting toward strike-slip faulting in deeper intervals below water-oil contact. The findings provide valuable insights into the region's reservoir development plans and seismic activities. The orientation of natural fractures suggests that horizontal wells drilled parallel to the orientation of SH can optimize wellbore stability. In addition, the stress variations and complexities observed in Field A are attributed to factors such as folding degree, lateral deformability contrasts, and geological structures like faults. The stress regime analysis indicates the influence of regional tectonic forces and the proximity to the collision boundary. This study will provide valuable insights into the exploration, development, and management of hydrocarbon resources in complex structure regions such as the Dezful Embayment, and it may contribute to understanding stress variations and distribution patterns in similar geological settings elsewhere.