Distribution Of Reservoir And Hydrocarbon Accumulation Of The Shahejie Formation In Northern Lixian Slope Of Jizhong Sag

Aiming to the difficulties in identifying reservoirs of sand-shale thin interbed of Shahejie Formation in northern Lixian Slope, based on seismic, drilling and logging data of the study area, and relevant theories like petroleum geology, sequence stratigraphy, sedimentology, etc., by using seismogeological integrative comprehensive research methods, this thesis does comprehensive studies on structural features, sedimentary systems, reservoir features, petroleum accumulation for identifying favorable reservoirs and target areas.By applying advanced technology in amplitude preservation and broadband processing with high resolution for 3D seismic data, the resolution and abundance of wave group data has been approved. Fine calibration, secondary fine calibration and well-tie comparison calibration have been conducted by applying various methods, and full-3D interpretation is done by using structural analysis theory, structural style and trap features.By applying sequence stratigraphy theory and technical methods, I establish an isochronal formation framework. As a result, the Shahejie Formation is divided into 7 fourth-order sequences: SQ7, or lower Sha-1 Member, corresponds to Lacustrine transgressive system tract and develops favorable sandbody of tail sandstone in lower Sha-1 Member; SQ6, or Sha-2 Member, corresponds to lowstand system tract; SQ5, or upper Sha-3 Submember, corresponds to highstand system tract and develops Es₃I sandgroup and Es₃II sandgroup which are favorable sandbodies.The sandbodies in underwater distributary channel of the braided stream delta are the most developed in this area. The major reservoir of lower Sha-1 submember is underwater distributary channel sandbody and beach-bar sandbody which are distributed in elliptic jointly in plane and formed by superimposition of multiple-phase lobate sandbodies; the major reservoirs of upper Sha-3 submember develop four underwater distributary channel sandbodies in the study area which distribute in a NW-ES banded shape.Due to reservoirs in this area are low-permeability reservoir, the lithology and physical property distribution of reservoir can be effectively predicted through applying reservoir feature inversion based on seismic, logging and geologic data. The pseudo-wave impedance data volume of self-potential can sensitively reflect the distribution feature of permeable sandstone.Pores of sandstones in this area dominated by secondary pores, characterized by intergranular dissolved pore, intragranular dissolved pore and moldic pore. Dissolution is the most important diagenesis for improving the porosity and permeability of reservoirs in this area. The moderate-porosity and low-permeability reservoirs are developed the lower part of Es₁ and the low-porosity and low-permeability reservoirs are developed in the upper part of Es₃.In this area, Shahejie Formation develops three suits of generation-reservoir -caprock assemblages, and the hydrocarbon migrates to Lixian slope through frame -sand bodies, faults, fractures, unconformity surface and composite carrier beds system. Distribution of structures and sandbody has good control over the petroleum accumulation. Based on distribution of structures, sedimentary phases and sandbodies, as well as reservoir accumulation rules, favorable regions have been delineated.