Hydrochemical and reservoir characteristics and genetic analysis of deep brines in the southwest margin of Qianbei Fault,Qianjiang Depression:A case study of the 4th Qianjiang Formation
The underground brine resources in Qianjiang Depression are rich in major elements,such as potassium,sodi-um as well as trace elements such as lithium,bromine,boron,iodine,rubidium,cesium and strontium,which have broad prospects for development and utilization.In this study,35 samples of underground deep brine and 12 samples of reservoir physical properties were collected from ZK01 well in Changhu area,southwest margin of Qianbei fault in Qianjiang sag.Through the test analysis results,the brine chemistry and reservoir characteristics and their causes are discussed.The re-sults show that the total dissolved solids(TDS)in the study area ranges from 80.70 to 148.45 g/L,with an average val-ue of 128.75 g/L,which belongs to low salinity.The TDS increases with the increase of brine depth.The main brine type is chloride type,followed by magnesium sulfate subtype.The Br-content of brine samples is 1.98-4.05 times of the com-prehensive evaluation index,which has a good development and utilization prospect.The study area is divided into five sandstone brine reservoirs,which belong to highultra-high porosity and medium-permeability reservoirs,with thickness ranging from 10 meters to 26 meters.The water barrier group is mainly composed of siltstone or mudstone,paste mudstone interlayer,belonging to low porosity,extremely low permeability water barrier,thickness from 27 meters to 64 meters.By analyzing the hydrochemical characteristic coefficient of the brines,it can be seen that the brines in the study area is loca-ted in the area with poor sealing and low metamorphism,and it is speculated that the brines come from the dissolution of halite,and each ion comes from halite,gypsum and clastic clay minerals,which is a typical leaching brine of the origin of continental salt lakes.
Qianjiang DepressionQianbei Faultthe 4th Qianjiang Formationdeep brineshydrochemical and reservoir characteristics
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