Reservoir architecture analysis of braided delta front developed in the long-axis gentle slope of faulted basin: A case study of the fifth Zaoyuan formation, Zaonan fault block, Zaoyuan Oilfield, Dagang

FENG Wenjie; LU Fengming; WU Shenghe; ZHANG Ying; MENG Qinglong; ZHANG Ke

Abstract：Based on core data,three-dimensional seismic data,well logging and dynamic production data of Zaonan fault block in Dagang oilfield,the architecture of braided river delta front developed in the long-axis gentle slope of faulted basin was analyzed by applying analytical hierarchy process,model guidance and static-dynamic method.A subdivision scheme covering the proximal part,middle part and distal part was proposed for braided delta front of this kind.The characteristics and differences of internal deposition architecture in different parts of the delta front were explained,and the refined sedimentary architecture model of the braided delta front developed in the long-axis gentle slope of faulted basin was established.The research results show that 1) The slope developed in faulted basin along the long axis was gentle.The sediment supply was sufficient,the water was at a low level and the delta front was wide.According to the hydrodynamic force and water depth of the delta front,as well as the sand body thickness,transverse connectivity,lithological characteristics of underground reservoirs,the delta front can be divided into proximal,middle and distal belts.2) In the proximal part,controlled by the large scale of distributary channels,strong hydrodynamic force and sufficient sediments,a massive and continuous mouth bar complex was formed.The single mouth bar developed several accretion sand bodies with a low angle of 3.8°,almost lack of outer edge and inner edge.Most distributary channels incised the mouth bar to its bottom and several small flood fans were formed at its lateral margin.Argillaceous cladding interlayer between accretion sand bodies and argillaceous interlayer of flood fan developed in the mouth bar.3) The distributary channels of proximal part branched into the middle part of delta front.The medium scale and isolated distribution of mouth bar complex was formed.Each single mouth bar could develop two or three accretion sand bodies with the progradation angles from 2.1° to 2.6°.Stacking modes of accretion sand bodies included progradation along the source direction and lateral accretion,which were controlled by the hydrodynamic intensity of distributary channels.Argillaceous cladding interlayer of progradation and lateral accretion developed between accretion sand bodies.4) In the distal part,the distributary channels branched again,leading to smaller scale,less sediment and frequent swing.The mouth bars were relatively small and isolated in distribution,which were completely separated by the argillaceous cladding interlayers.