Oil & Gas Geology ›› 2017, Vol. 38 ›› Issue (1): 71-78.doi: 10.11743/ogg20170108

• Petroleum Geology • Previous Articles     Next Articles

Characteristics and controlling factors of fan delta facies low permeability reservoirs in Bohai A oilfield, the Bohai Bay Basin

Zhou Junliang, Hu Yong, Li Chao, Fu Rong, Lai Youchun   

  1. Bohai Oilfield Research Institute, CNOOC China Limited, Tianjin Branch, Tianjin 300459, China
  • Received:2016-01-15 Revised:2016-12-28 Online:2017-02-28 Published:2017-02-27

Abstract:

In order to understand reservoir characteristics and controlling factors of the lower 3rd Member of Shahejie Formation(E2s3L) in Bohai A oilfield,we studied the lithological composition,pore types and structure,porosity and permeability distribution and discussed the controlling factors of petrophysical properties of the reservoirs from sedimentary,diagenetic and tectonic perspectives based on thin section,scanning electron microscopy (SEM),mercury injection and other conventional lab test data.The results show that the reservoirs of fan delta facies in E2s3L have low to ultra-low poro-sity and ultra-low permeability.They are composed of lithic arkosic sandstone with low compositional maturity,their main pore throat types are primary intergranular pore,dissolution pore and residual pore,and the pore throat structure is fine to micro.The reservoir properties were controlled by various factors,including sedimentation,dissolution and tectonic movements etc.Sedimentary environment of distributary channel and mouth bar at fan delta front controlled the grain size and sorting of the reservoir,resulting in relatively good reservoir properties.Compaction and cementation were the main factors causing the low permeability,however,dissolution of feldspar and detritus components by organic acids formed secondary pores,and the abnormal high pressure in the reservoir weakened compaction and helped the preservation of primary intergranular pores.Fractures are well developed near the faults formed by various tectonic movements,which also helped to improve the physical properity of the reservoirs.Through comprehensive analysis of all available data,we can conclude that strong hydrodynamic depositional environment,later dissolution and well-developed fracture network are the main factors that control the formation of the reservoirs with relatively high porosity and permeability.

Key words: diagenesis, physical properity, Shahejie Formation, fan delta, Bohai Bay Basin

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