Abstract
The stress field is a complex variable that affects all drilling operations, completions and reservoir performance. From the three components of a non-rotated stress field, the maximum horizontal stress is the more difficult variable to model since cannot be directly measured and involves multiple unknowns. This study presents an advanced geomechanics modeling technique to estimate the most likely horizontal stresses by integrating advanced acoustic measurements, multi-well image interpretation and geomechanics back analysis.
The study was carried out in SR wells, a new development zone in the UAE, which targets the fractured and medium porosity reservoirs rocks of Late Permian formation. The estimation of the stress field is necessary not only for well planning but also to understand the occurrence of abundant drilling induced fractures that sometimes mask the natural ones. It will help also to propose location of possible fracture treatments while analyzing possible relationships between fluid flow and the presence of critically stressed fractures.
The horizontal stress field was inverted from advanced geomechanics modeling including the elimination of the gas effect, inversion of Shmax from 3-Shear moduli analysis in stress sensitive intervals, image interpretation for stress related and intrinsic features, determination of stress regime Q-factor from Integrated Stress Analysis (ISA) and performing a failure analysis to validate the stress field and calibrating the overall geomechanical model. The calculated maximum horizontal stress from 3-Shear moduli, ISA and failure analysis proved to be consistent in both SR wells, where the Normal stress regime agreed with current structural framework and local geology. The stress direction was also consistent among measurements, although some local stress rotations were observed in specific zones. High angle features such as drilling induced and natural fractures were also consistent with the modeled stress field, where the vertical stress is the maximum principal stress. Mud losses were mainly attributed to the presence of vugs, conductive seams and fracture corridors rather than induced fracturing.
The inverted stress field was finally used as input in the Completion Advisor and Fracture Stability workflows and then compared against PLT data in. The results show a good correlation between critically stressed fractures and well productivity in SR wells. The last could lead to optimize the completion strategy in future wells by selecting best intervals for perforating and stimulation based in this integrated approach.
