Spatial and Temporal Evolution of Submarine Lobe Deposits and Their Grain-Fabric

Abstract

Submarine lobes are a major component of submarine fans and of economic interest because of their potential as hydrocarbon reservoirs. To enhance reservoir predictions it is important to improve the understanding of their dimensions, grain-size distribution and depositional evolution. While outcrops and seismic datasets allow the in-depth study of lobe facies, internal architecture and plan-view geometries, they do not allow for the study of the influence of flow conditions and basin set-up that led to these deposits.

Ten flume experiments were conducted in the 6x11 m Eurotank flume to study the depositional characteristics and grain-size distribution of lobate deposits associated with 1) different basin floor dipping angles (0-4°), 2) different sediment concentration of the parent turbidity current (11-19 % Vol), and 3) varying discharge (20 - 40 m³/h). Data analyses focused on lobe dimensions, the location of the depocentre, the grain-size distribution within the deposits, and temporal deposit evolution.

The experimental turbidity currents formed distinctive lobate-shaped deposits with a strong dependency of the morphology and grain-size distribution on the basin set-up and initial flow conditions. In most runs deposition started away from the break-of-slope and subsequently backstepped until the lobe onlapped onto the slope. Generally, six relationships can be observed: 1) with increasing basin-floor dip the lobe length and aspect ratio (L/W) increase; 2) lobe length is proportional to the sediment concentration of the flow; 3) increasing sediment discharges lead to longer lobe bodies and influences onlap position; 4 ) as the L/W aspect-ratio increases the main depocentre of the lobe shifts to more distal areas; 5) lobe width remains similar over all runs and is therefore proposed to be primarily dependent on grain size; and 6) grain-size fining occurs more rapidly to the lateral lobe margins than to the frontal margins.

The results of the conducted experiments enable the determination of grain-size fabric development and potential waste zones in relation to the deposit geometry. This will essentially decrease uncertainties during hydrocarbon field appraisal and development of submarine fans.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018