Many fractured carbonate reservoirs of Abu Dhabi have different structural styles and exhibit unpredicted behavior for development-production realizations. We have studied one of these reservoirs that comprise a domal structure with very gentle dipping flanks, and high fractures density. These fractures play an important role in controlling fluid flow and recovery.
In this study, we present a conceptual model that explains the fracturing mechanism; formation, development and reactivations of these fractures. It also provides answers to questions about the main factors that control fracture geometries and densities with respect to reservoir structure and rock typing. Based on the available data from 2D seismics and cores examination, fracture systems identification and classification were carried out. We have also discussed the relationships between these fracture systems with curvature, faults and shear zones.
We believe that fracturing mechanism is mainly controlled by reactivations of the pre-existing basement faults (structural grain), which have been reflected throughout the sedimentary cover as two main fractures systems each of which comprises three fracture sets: one extensional and two conjugate shear ones. It is evident that curvature of doming whether on the crest (convexity) or on the flanks (concavity) have no major effect on fracture densities. Instead, fracture densities increase in the vicinity of faults or shear zones. Fracture densities also increase in dolomitic layers compared to limestones and anhydrates.
This new fracturing concept has a significant impact on production and recovery, where different scenarios for fractures opening/reactivations due to the present state of stresses are presented.