Investigation of fractured carbonate reservoirs by applying shear-wave splitting concept

Abstract

In this study, fracture orientations in carbonate reservoirs were determined using a multicomponent velocity analysis based on shear wave splitting. The analysis is based on the estimated velocities of large seismic events with different polarizations. In a fractured zone with a dominant orientation, weak amplitude split shear events, including shear noise, result in shear waves that are polarized toward the symmetry and anisotropy axes and propagate with a common fast and slow velocity, respectively. Thus, a velocity stack should show high coherency anomalies in directions parallel and orthogonal to the fracture strike. Furthermore, because the analysis is applied locally at a specific depth range, it is less susceptible to the effects of overburden anisotropy and noise. The dominant fracture orientations from carbonate reservoirs of four oilfields were compared to those interpreted from fullbore microimager and core data. Fractures in two offshore reservoirs strike NNE-SSW and NW-SE, which are related to Zagros stress. Fractures in two onshore reservoir strikes NE-SW, while in deeper onshore reservoir fractures are aligned with N-S direction. The findings of this study are promising, particularly for the fractured reservoirs especially those located in Abu Dhabi, which are characterized by high heterogeneity and complex fracture network related to complex tectonic history. In order to obtain geometrical parameters of fractures at seismic scale, it is recommended to implement the analysis adapted in this study after acquiring three component zero-offset vertical seismic profiling.

Mechanisms of Stress Sensitivity on Artificial Fracture Conductivity in the Flowback Stage of Shale Gas Wells

“…For instance, Bouchaala used seismic attenuation anisotropy to separate open and closed fractures [25]. Furthermore, Diaz-Acosta combined shear wave splitting and multicomponent velocity analysis to determine fracture orientations in reservoir zones [26]. However, all this research lacked quantitative evaluation on proppant backflow, fragmentation, and embedment.…”

Multi-Scale and Multi-Dimensional Imaging of Mineral Matrix Pore-Fracture Networks in Lower-Thermal-Maturity Lacustrine Shale: Examples from the Paleogene Shahejie Formation, Bohai Bay Basin

“…Recent developments in Ar-ion-beam milling + field emission scanning electron microscope (FESEM) systems allow for 2D visualization and qualitative analysis of a variety of shales with large field and high resolution . Furthermore, the focused ion beam scanning electron microscopy (FIBSEM) (so-called “slice-and-view” technique) and X-ray computed tomography (CT) allow the 3D reconstruction of the microstructure of porous space of shale. − The traditional CT methods, such as X-ray centimeter-tomography (Macro-CT) and X-ray millimeter-tomography (Meso-CT), have limited space resolution and can only reveal the shale beddings and large-scale cracks. Both Macro-CT and Meso-CT have been used to image pores and fractures in coarse-grained rocks, such as limestone and sandstone or used to image laminar structures in fine-grained shales .…”

Seismic Anisotropy Assessment based on Machine Learning Approaches

“…At seismic scale, Newrick et al 5 and Liu et al 6 succeed to estimate anisotropy parameters from travel time of first arrivals extracted from walkway VSP dataset. In order to remove the overburden effect on anisotropy estimation, Diaz-Acosta et al 7 analysed split shear waves by conducting a multicomponent S wave velocity analysis on zero-offset VSP data. The scholars succeed to calculate fracture orientation within a carbonate reservoir in Abu Dhabi.…”