Multi-scale, multidisciplinary analysis of mass-transport complex (MTC) emplacement and structure

Abstract

Mass-transport complexes (MTCs) refer to seismically-chaotic deposits generated by large-scale gravity flows, and form one of the most sedimentologically- and seismically- distinctive depositional elements in deep-water depositional systems. This thesis aims to provide a novel approach to the study of multi-scale MTCs in (i) a salt-confined minibasin, and (ii) a salt-free, relatively un-confined basin, focusing on MTC morphology, kinematic indicators, petrophysical properties and flow process. To achieve these aims, I use high-quality seismic reflection datasets, and borehole data from the northern Gulf of Mexico and offshore NW Australia to investigate: (i) the geometries, spatial distribution and kinematic indicators of MTCs; (ii) the complex interactions between the occurrence of MTCs and salt halokinesis; (iii) the petrophysical properties and sealing potenials of MTCs; and (iv) the detailed formation process of giant coherent blocks in MTCs. The first technical chapter presents a generic model that emphasises the dynamic nature of minibasin evolution, and how MTC emplacement relates to halokinetic sequence development. The second technical chapter investigates the petrophysical properties of MTCs, especially their basal shear zones. The third technical chapter investigates a submarine spread deposit that contains giant coherent blocks in a low gradient, basin floor setting. For hydrocarbon exploration, the results contribute to understanding the sealing capacity of MTCs. This includes valuable methodologies that combine seismic reflection and petrophysical data to recognise and predict the most compacted and least permeable intervals (the basal shear zone) in MTC. The recognition of the basal shear zone could help the offshore drilling community to optimise well planning and borehole stability. In terms of geohazard prevention, a better understanding of the formation of the blocks in MTCs will provide crucial information for where future failure might occur and help to reduce the damage of associated with MTCs to the offshore infrastructures (e.g. pipelines and drilling rigs).Open Acces