Numerical Simulation Study Of Sediment Waves From Turbidity Currents

Turbidites, the deposits from turbidity currents, not only shape the importanttopography of the submarine canyons and the submarine fans, but also in many cases arethe reservoirs for hydrocarbon resources. Much progress has been made for the study ofthe turbidity currents and turbidites in recent decades. With the development of computertechnology and numerical simulation, numerical simulation gradually becomes animportant method for the study of the flow and deposition of turbidity currents. In thispaper, the characteristics of flow and deposition of turbidity currents with multi-sizeclasses of particles under different inflow mechanisms (sudden release, continuousinflow), flowing on different topography (slope, flat, wavy and measured terrain) wereinvestigated through numerical simulation. The numerical model is based on the Reynoldsaveraged Navier-Stokes equations coupled with buoyancy modified turbulence k-ε model.The investigation of sudden-release and sustained-inflow turbidity currents flowing from aslope to a horizontal wavy topography shows that:(1) the deposition from turbiditycurrents with both sudden-release and sustained-inflow mechanisms with the same totaldischarge shows the same upstream migration of sediment wave due to differentialdeposition, more on the upslope and less on the lee-side of each waveform;(2) comparedwith continuous-inflow type, sudden-release turbidity currents deposits more in thedownstream due to losing of sediment, and thus driving force with time; the distributionof the particle size in the vertical direction is inverse-graded with larger particles depositedon top at each sudden-release event;(3) for a turbidity current with sustained inflow, itmaintains relatively stable concentration and speed, no obvious vertical size variation isobserved, but it presents more clear downstream fining characteristic.The characteristics of flow and deposition of sudden-release turbidity currents withmulti-size classes of particles under ambient fluid density stratification from a slopeflowing to a horizontal flat bed were investigated, and comparative studies also made withsudden-release event and sustain-inflow event without stratification on the sametopography, the result shows that:(1) with ambient fluid density stratification, the velocityand concentration of the head of sudden-release turbidity currents are higher;(2) with orwithout ambient fluid density stratification, sediment waves form on the front parts ofslope and flat topography under multiple sudden-release events; and the deposit forambient fluid with density stratification are higher than that without stratification;(3) nosediment waves observed for multiple sustained-inflow turbidity currents on the sametopography without ambient fluid density stratification;(4) although for all cases theparticle size of deposit decreases gradually downstream, for each sudden-release event, larger particles deposited more around sediment waves,while more clear downstreamfining was observed for sustained-inflow turbidity currents. At last, it is simulated the flowand deposition of turbidity current on the Kramis deposition fan. The characteristicsrevealed by these simulations may assist us in reconstructing the ancient environment,deducing the mechanisms of turbidity currents and the scale of possible oil and gasreservoirs based on the characteristics of the turbidite obtained by field outcropobservation or drilling survey.