Dynamics System Of Petroleum Accumulation In The Linnan Depression

The Ninnan Depression is located at the northern-west part of the Huimin Depression, Bohaiwan Basin. It is a typical fault-folded depression, characterized by multi-petroleum-bearing seams, widely distributed oil source rocks, complicated structures and variable types of petroleum pools. For these reasons, there have been lack of a deep understanding on the petroleum pool formation patterns for a long time and scientific ideas for further exploration in this depression. In this study, a method of dynamics system of petroleum accumulation, which integrates the information from petroleum geology, sequence stratigrapy, organic geochemistry and geophysics, with fluid dynamics, has been applied to investigate the petroleum pool formation conditions and models in this area. The following main results have been obtained:(1). The elements of dynamics of petroleum accumulation in the Linnan depression were investigated, including source rocks, reservoir rocks, cap rocks, trapping structures, and pore fluid pressure. On the base of this, four sets of dynamics systems of petroleum accumulation were recognized. There are: lower half closed dynamics systems with high pressure and self-sources; middle lower half closed dynamics systems with high pressure and self or other sources; middle upper half-closed dynamics systems with high-normal pressure and other sources; and upper half- open closed dynamics systems with a normal pressure and other sources .(2) The main oil source rocks are ES33-ES23 dark mudstone. The main stage of oil generation of this set of source rocks occurred during -7 Ma to -1 Ma, corresponding to a burial depth of 3500-4000 m.(3). The channel system is consisted of faults, sandstone, unconformable surfaces and volcano aggressive rocks. Petroleum migration patterns include side, vertical and mixed direction. The petroleum pools formed after -5 Ma.(4). There types of petroleum pool formation models were recognized. They are side migration accumulation model, vertical migration accumulation model and mixed migration accumulation. The lower dynamics systems and middle-lower dynamics systems are believed to have great petroleum prospective. It is suggested that hidden petroleum pools should be main targets for further exploration.These results not only give a guide to the petroleum evaluation and exploration in the Linnan Depression, but also provide a case study on dynamics system of petroleum accumulation for the Tertiary petroleum-bearing basins.