Dynamic Changes of Palaeotopography and Their Control on the Migration of Delta Lobe - Research on Liaoxi Low Uplift of Bohai Gulf Basin, China

Guo, Tao ¹; Zhou, Xinhuai ¹; Lai, Weicheng ¹
(1) Exlporation and Development Research Institute of CNOOC Ltd., Tianjin, China.

The control of palaeotopography on the distribution of sandbodies has been well studied in continental rift-subsidence basin, While the research on the dynamic changes of palaeotopography caused by unbalanced tectonic movement in the sequence framework and their control on the migration of delta lobe are quite few. This paper discusses how it works by taking Liaoxi low uplift of Bohai Gulf Basin in China as an example. Liaoxi low uplift is controlled by the north-southward boundary fault, with two sags on both sides of the uplift. Traditionally, it is regarded that there is no deposition from west because of the obstruction of the boundary fault, and the reservoir of Dongying Formation is constructed by the delta that is distributed along the slope north-southward. But new evidence indicates that the north-southward delta is pseudomorphism resulting from the lateral migration of three east-westward delta lobes. The three lobes correspond with three topographic lows which are controlled by three adjusting belts from north to south due to the unbalanced movement of the boundary fault of low uplift. Further study based on high resolution sequence analysis shows that the movement of boundary fault is unbalanced horizontally and spatially. The lateral migration of delta lobes in different system tracts is controlled by the dynamic changes of palaeogene affected by faults. During low system tract of Dongying formation, the growth index of boundary fault in the north accommodation zone is low, while those of the middle and south are high. So it is easy for sediment migrating from west to the uplift through the north least-active accommodation zone, and it is blocked in the middle and south zones. As a result, deltas are well developed in the northern part and less developed in the mid-southern part of the uplift. During transgressive system tract, the fault growth index of middle accommodation zone is low and deltas are dominantly developed in this area and less developed in the other two accommodation zones. During high system tract, the fault growth index in middle-south zones are low, correspondingly deltas are well developed in theses areas. The deltas are controlled by the dynamic changes in time(sequence position) and space(palaeogeomorphology) of the provenance. The detailed study of the delta migration can not only help to discover the main controlling factors of petroleum accumulation, but also identify the exploration direction of subtle reservoir.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.