Oil & Gas Geology ›› 2005, Vol. 26 ›› Issue (4): 473-479.doi: 10.11743/ogg20050413

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Resrvoiring characteristics and main controlling factors for deep hydrocarbon accumulations in Bonan sag in Jiyang depression

Gong Xiumei1,2, Jin Zhijun3, Zeng Jianhui1,2, Qiu Nansheng1,2   

  1. 1. Basin & Reservoir Research Center, China University of Petroleum, Beijing;
    2. Key Laboratory of Petroleum Accumulation, Ministry of Education, Beijing;
    3. Exploration & Production Research Institute SINOPEC, Beijing
  • Received:2005-07-25 Online:2005-08-25 Published:2012-01-16

Abstract:

In Bonan sag,the deep source rocks are predominantly dark shale,sandy shale and evaporites in the 4th member of Paleogene Shahejie Fm,with the TOC content of 0.9%-2.39% and kerogens of type iv and 1;the deep reservoir rocks are mainly composed of glutinite,fine sandstone and muddy limestone in the 4th member of Shahejie Fm,with the porosity of 1.18%-23.5% and permeability of 0.1×10-3-36.67×10-3μm2.According to trap types,the deep oil-gas pools in Bonan sag can be divided into lithologic trap and composite trap oil-gas pools;based on types of source rock,they can be divided into oil-gas pools sourced by Paleogene sapropel-type source rocks and sourced by Paleo-Mesozoic coal measures(i.e.coal-derived gas pools);in the light of source-reservoir-cap rock combinations,they can be divided into "self-sourcing and self-reservoring"type oil-gas pools(i.e.both the source rocks and reservoir rocks are in the 4th member of Shahejie Fm),and "upper-sourcing and lower-reservoiring"type oil-gas pools(i.e.the oil-gas pools with the source rocks in the 3rd member of Shahejie Fm and reservoir rocks in the 4th member of Shahejie Fm). Their reservoiring process is controlled dominantly by charging stages,fluid dynamic systems and evaporite layers.The continuous late-stage charging has provided huge quantities of hydrocarbons for deep reservoiring.The unique dynamic systems of overpressure fluid in deep strata have provided the driving force for hydrocarbons migration and accumulation.The control of evaporites on oil and gas accumulations is represented by (1) acting as regional seal rocks,(2) delaying the diagenetic process of underlying strata and improving the poroperm characteristics of reservoir rocks and(3) conducing to the formation of overpressure fluid systems.Therefore,the strata overlain by evaporites are favorable targets for deep oil and gas exploration.

Key words: reservoiring characteristics, main controlling factor, deep layer, Bonan sag

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