A Numerical Approach to the Effect of Different Clay Types on the Properties of Cohesive Sediment Gravity Flows and Their Deposits
In the natural environment, sediment gravity flows (SGFs) can behave as turbidity currents, transitional flows, and debris flows. SGFs are the most important mechanism for transporting sediment, including sand, into the deep sea and thus the main process leading to the formation of oil and gas reservoirs in deep water deposits. SGFs are difficult to study in the modern environment, whereas scaling issues, unrealistic geometries, and short durations typically hamper laboratory representations of these flows. Computational fluid dynamics (CFD) are able to fill the gap between small and large scale, integrating data from theory, nature, and experiments. The deterministic process software MassFLOW-3D™ has been developed and successfully used to construct a 3D model for the simulation of turbidity currents, thus allowing all principal hydraulic properties of the flow and its responses to topography to be monitored in 3D over the whole duration of the turbidity current. The present project aims to further analyze turbidity currents numerically and extend the validation of the code to transitional flows and debris flows, taking into account their simultaneous occurrence within the same depositional basin and transformation between flow types. The current project uses laboratory data obtained from lock-exchange tank experiments at Bangor University. These experiments contrasted SGFs composed of kaolinite clay (weakly cohesive) and bentonite clay (strongly cohesive) at a range of volumetric concentrations in seawater. In each experiment, information on clay concentration, head velocity, flow turbulence, and deposit properties were obtained. In addition, rheological tests were conducted on clay samples with the same initial composition as the experimental flows, to obtain flow viscosity and yield stress. Thus, the flume experiments provided an extensive database that accurately describes each flow. The modeling was directed towards understanding the viscoplastic effects of the clay on each flow and recreating numerically the flow behavior and the depositional pattern observed in the laboratory for high-, medium-, and low-density SGFs using non-Newtonian viscosity models, such as Bingham and Herschel-Bulkley models. The effect of clay concentration on the competition between cohesive and turbulent forces was also tested.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019