Implications of Fracture Networks in Elastic Response of Heterogeneous Carbonate Reservoirs

Abstract

In this research, we explored how various fracture parameters could influence the elastic response of heterogeneous carbonates. Herein, 16 core plugs from a fractured carbonate formation are subjected to a comprehensive analysis including CT-scanning, optical and electron microscopy, and XRD analysis to identify and characterize open fractures and their corresponding features. Subsequently, these samples underwent hydrostatic compression under reservoir conditions, during which ultrasonic wave velocities and strain were continuously measured while confining pressure was gradually increased to 65 MPa, pore pressure remained constant at zero, and temperature at 90°C. Our findings revealed that the presence of open fractures would cause a reduction in both compressional and shear wave velocities while causing strain variations. The extent of these changes, however, is notably influenced by fracture parameters, particularly connectivity, dip, and aperture. Furthermore, the study showed that the influence of stylolites and solution seams is the secondary influential factor, primarily impacting the P-wave and increasing the strain. This research suggests that the impact of structural features, especially fractures, supersedes the role of porosity percentage in controlling the elastic properties of carbonate rocks. Furthermore, it was concluded that when fractures form a network, they exert a more pronounced impact on the elastic response compared to their isolated existence. This observation confirms that detection of fractures should be supplemented with a detailed assessment of their parameters. Collectively, this study provides valuable insights into how distinct fracture parameters would improve our interpretation of carbonate reservoirs elastic response, with a particular focus on wave velocities.