De-Risking the Full Development Cycle of Tight Naturally Fractured Prospects by Integration of Advanced GeoMechanical and Natural Fracture Characterization: A North African Perspective

Abstract

Abstract To de-risk the development of two tight naturally fractured plays in North Africa, comprehensive geomechanical and natural fracture characterizations of target formations were performed. A wide range of advanced formation evaluation measurements were used as input in the analyses, and the integrated analysis results were utilized in the optimization of the full development cycles of these prospects from drilling to production. Anisotropic geomechanical characterizations of prospect wells were performed using cross-dipole acoustic logs as the inputs for Vertical Transverse Isotropic (VTI) models. In-situ stress measurements acquired by straddle packer wireline tool along with anisotropic rock mechanical tests and natural fractures identified from image logs were integrated to build robust stress, rock mechanical properties and natural fracture models. The developed models were then used to run multiple workflows i.e. wellbore stability analysis, critically-stressed fracture analysis and perforation optimization. Eventually, the results of these workflows were applied to enhance decision-making process in different stages of development in these plays. Stress regime in the target formations were estimated to be transitional strike-slip/ reverse faulting with significant vertical anisotropy between different lithological units. Presence of reverse faulting regime in some intervals of the target formations were identified as a potential geohazard due to the likelihood of development of pancake hydraulic fractures while stimulating. The observed lateral perturbation of horizontal stress direction was correlated with the proximity to structural elements like faults and this could be validated by instances of breakouts rotation identified from image logs. This knowledge of stress direction variability was applied to optimize the trajectory of horizontal wells. In deviated wellbores, preferred trajectories were identified to minimize potential instability during drilling and to maximize contribution of existing natural fractures during production. Drilling mud weights were also optimized to reduce the risk of instability and to indirectly increase the chance of stimulation success by improving hole quality. Influence of critically-stressed natural fractures on productivity and fraccability of perforated intervals were validated using available production data and observed breakdown pressures. It was found that highly dipping natural fractures are the dominant factor in easing breakdown during stimulation and in improving subsequent production. These validated models were utilized to optimize the selection of perforation intervals as well as to identify the desired stimulation pressures to enhance fraccability and productivity of target formations by leveraging the hydraulic conductivity of existing natural fracture corridors. Advanced data acquisition programs helped to improve the robustness of geomechanical and natural fracture characterizations of two tight fractured prospects. Integration of these models was the basis for application of multiple workflows whose results led to pragmatic de-risking of different stages of development in these plays by optimizing decision making processes.