This study aims to characterize the fracture network in altered Oligocene-Early Miocene basalts of the Jizan Group, which accumulated in half grabens during the continental rift stage of Red Sea evolution. Unlike fresh basalts, the Jizan Group was affected by low temperature hydrothermal metamorphism, which plugged the original matrix porosity in vesicles, breccias, and interflow layers with alteration minerals. However, the basalts are pervasively shattered by closely spaced fractures in several directions, which provide fracture permeability. Characterization of these fractures is essential to reducing the fracture permeability uncertainty for mineral carbonation by the dissolved CO2 process such as Carbfix.
Conventional fracture orientation and densities were initially taken at outcrops of the Jizan Group to characterize the fracture network. Terrestrial Digital Photogrammetry (TDP) and Unmanned Aerial Vehicle Digital Photogrammetry (UAVDP) surveys were conducted to acquire images covering larger areas to create 2D orthoimages and 3D models of the outcrops using Agisoft Metashape, which were analyzed for fracture geometries using QGIS and Cloud Compare, respectively. The automated analysis of fracture orientations and densities compared well with conventional manual measurements.
Similar fracture geometries were observed at seven different sites along the outcrop belt of the Jizan Group, which suggests a common origin. This study found four dominating fracture sets in the Jizan Group volcanics, with a dominant trend of fractures in the NNW direction, similar to the general trend of the Red Sea. The Northern sites presented higher fracture intensity compared to the southern sites, indicating more suitable environments for carbon mineralization.
Moreover, mineralogical composition of spatially distributed samples collected from the Jizan Group volcanics were collected to investigate spatial distributions of secondary alteration minerals in the Jizan Group basalts. Epidote was observed in samples collected from southern outcrops indicating hydrothermal alteration temperatures higher than 230 C, whereas the northern sites lacked epidote and contained calcite indicating lower hydrothermal alteration temperatures. The presence of sufficient amounts of Ca according to previous studies conducted by Torres (2020), along with potential 3D fracture networks in the subsurface indicate feasibility for the injection of CO2 charged fluids in the subsurface of the volcanics.
|Date of Award||Sep 2021|
|Original language||English (US)|
|Supervisor||Abdulkader Alafifi (Supervisor)|