Study On Reservoir Characteristics Of The Cretaceous Qingshuihe Formation In Chepaizi Area,Junggar Basin

The Qingshuihe Formation sandstones in Junggar Basin have aboundant oil and gas resources and great exploration potential.It is an important exploration field of our country in oil and gas reserves growth in the near future.Strengthening the study of its reservoir characteristics and main controlling factors could provide plentiful basic data for exploration of the oil and gas in this basin.According to the previous studies and comprehensive theory of sedimentology and petrology,the pore type discrimination,porosity and permeability testing of Qingshuihe Formation sandstones in Junggar Basin were systematically analyzed in this thesis through the tests of thin sections,scanning electron microscope,high pressure mercury injection and core analysis.Combined with whole rock XRD data,the effects of diagenesis and mineral compositions on the reservoir physical characteristics were clearly analyzed.The results showed that the rock types of Qingshuihe Formation sandstones in Junggar Basin were dominated by feldspathic litharenite sandstones,followed by lithic sandstones,which are characterized with low textural maturity and composition maturity.The porosity ranges from 15% to 25%,and the average porosity is 19%.The effective air permeability is from 5 to 50 mD,and the average permeability is 38 mD.It belongs to the midium porosity and low permeability reservoir,but there are some reservoir beds with high permeability.The pore throats were relatively well sorted and the mid pore throat type is the most developed with well pore connectivity.Qingshuihe Formation sandstones reservoirs mainly experienced compaction,cementation,and dissolution.The reservoir diagenetic stage now is from the end of the early diagenetic stage B period to the beginning of the mid diagenetic stage A.Compaction and cementation are the main causes of the damage of reservoir properties in the study area,while the dissolution improved the physical property effectively.Simultaneously,the reservoir is also controlled by its provenance,lithology,sedimentary,etc.The favorable exploration area of Qingshuihe Formation sandstones in Junggar Basin was predicted based on the comprehensive analyses of reservoir controlling factors and the superposition map of porosity and permeability.