Quantitative Analysis of Sublacustrine Fan in Lacustrine Transgressive System Tract by Numerical Sedimentary Simulation, Take LiaoZhong Sag as an Example in Bohai Bay, China

Abstract

The sublacustrine fan, as an important type of lithologic reservoir in rift lake basin, are influenced by topography, water level fluntuation and wave action. Whereas, there are some sublacustrine fans existed in lacustrine transgressive system tract of the Dongying formation of LiaoZhong sag in Bohai Bay. In this study, a numerical sedimentary simulation is carried out by using the software of Dionisos and by synthesizing the cores, well logging, seismic data, modern sedimentary instances and flume physical experiment in the second member of the Dongying formation of LiaoZhong sag, so as to carry out the quantitative analysis of the distribution of the sublacustrine fan. The current study find that affected by the early unstable delta, strong hydrodynamic conditions and high angle of the depositional slope-break belt, the sublacustrine fans in the study area experienced twice accumulation along the slope. In the first phase of the sublacustrine fan, sand bodies were transported into the basin from the north and east, and deposited in oval shape under the terrain break. The distribution of the sublacustrine fan covers an area of 25 square, channel characteristics is not obvious, the sandstone percentage located in fan is highest 45%. Whereafter, the lake level continued to rise and formed a set of thin layer of mudstone, which developed largest thickness in the center of the basin and thinning out towards the shore. After the lake level continued to rise to the top, because of the strongest hydrodynamic conditions, the second phase of sublacustrine fan sand bodies were continuously pushed into the lake and presented two sedimentary centers, the distribution of the sublacustrine fan covers an area of 35 square, which have two channels, width mostly up to 1000 meters, and the sandstone percentage located in channel is highest 70%. The result of simulation also indicates that there is an optimum slope angle (9 to 12 degree) for the formation of sublacustrine fan, and this may be the important factor for the causal mechanisms of the sublacustrine fan in lacustrine transgressive system tract. The changing amplitude of relative lake level appears to control the thickness and transportation distance changes of sublacustrine fan sand body.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015