Research On Control Factors Of Chang-8 Relatively High Permeability Reservoir In Zhijing Area

Based on the basic data,this paper adopts the research ideas of combining static geological analysis with dynamic process,combining whole and part,and combining macro research with micro research.A large number of analytical tests were carried out to study the sedimentary characteristics and microscopic characteristics of reservoirs.Based on conventional casting thin sections,physical properties,mercury injection analysis and core observation,combined with scanning electron microscopy,clay mineral analysis and other test techniques,the genesis of low permeability reservoirs and the control factors of relatively high permeability and high quality reservoirs were explored from two aspects of sedimentation and diagenesis.The results show that:（1）The structure of Chang 8 member in the study area is gentle as a whole,showing a northeast high southwest low monoclinic,and the thickness of each small layer is stable,with an average of 40 meter.（2）The sandstone types of Chang 8 reservoir are mainly feldspar sandstone and lithic feldspar sandstone.The content of chlorite and iron calcite is large.The pore types are mainly intergranular pores and feldspar dissolved pores.The porosity is between 2.38%～18%,and the permeability is between（0.01～3.87）×10^-3μm².The reservoir type belongs to low porosity,ultra-low porosity and ultra-low permeability reservoir with strong heterogeneity.（3）According to the sedimentary characteristics,the Chang 8 section of the study area is divided into multiple sedimentary microfacies such as underwater distributary channel,underwater natural levee and interdistributary bay.The sand bodies in the study area are vertically superimposed by multi-stage sand bodies,and are distributed in a northeast-southwest band on the plane.（4）The Chang 8 member of the study area is delta front deposit,developing gray green-gray sandstone.According to the sedimentary characteristics,the Chang 8 section of the study area is divided into multiple sedimentary microfacies such as underwater distributary channel,underwater natural levee and interdistributary bay.The sand bodies in the study area are vertically superimposed by multi-stage sand bodies and horizontally distributed in NE-SW strips.（5）Combined with sedimentary microfacies,diagenetic facies and reservoir physical properties,the Chang 8 member of the study area is divided into three types of reservoirs.Type Ⅰ reservoir belongs to the main part of underwater distributary channel.The thickness of sand body is greater than 16 meter,the porosity is greater than 10%,and the permeability is greater than 1×10^-3μm².The type Ⅱ reservoir belongs to the flank of the underwater distributary channel.The thickness of the sand body is between 8～16 meter,the porosity is between 8%and 10%,and the permeability is between（0.3～1）×10^-3μm².The type Ⅲ reservoir belongs to the interdistributary bay.The thickness of the sand body is between 4～8 meter,the porosity is between 5%～8%,and the permeability is less than 0.3×10^-3μm².