The Research Of Sandstone Diagenesis And Diagenetic Fluid Of The Xujiahe Formation In The Central Of Sichuan Basin

Through experimental analysis and testing techniques,using the SEM of diagenetic clay minerals,temperature and composition of fluid inclusions,carbon and oxygen isotopes,et al.,the diagenesis of the sandstone of the Xujiahe Formation in the Sichuan Basin and the quartz secondary increase and carbonate cement fluid environment indication Comprehensive analysis of the process.The research results are as follows:The main rock types of the Xujiahe Formation in central Sichuan are lithic quartz sandstone and lithic sandstone,which are sandstone reservoirs with low composition maturity and high structural maturity.The clay mineral combination is mainly illite,chlorite,kaolinite and Illite-Montmorillonite mixed layer.The cement is quartz secondary enlargement,carbonate cementation and chlorite cementation.Sandstone reservoirs mainly undergo physical?chemical?compaction,dissolution of feldspar and cuttings,cementation and dissolution of clay minerals and carbonates,and secondary cementation of quartz during burial.The overall physical properties of the reservoir are poor,which is characterized by low-porosity and low-permeability reservoirs,and also reflects the compacted and dense characteristics of the Xujiahe Formation sandstone reservoir.With reference to the PTt trajectory of metamorphism in metamorphic rocks,this research method was introduced into the study of diagenesis and the concept of DTt was proposed.Quantitative study of diagenesis.It can be seen from the DTt trajectory that as the depth increases during the diagenetic period,the renewal temperature of the age increases.Quartz secondary increased the inclusion of medium-high temperature-medium-low salinity characteristics,medium-high temperature characteristics indicate thermal fluid activity,and is related to magmatism;medium-low salinity indicates that diagenetic fluid is dominated by formation water.Both temperature and salinity have a peak,indicating that only one thermal fluid activity is experienced during the formation of quartz secondary enlargement.A few individual samples have slightly higher temperature and salinity,which may be related to external fluid charging.The laser Raman test did not detect the presence of hydrocarbon inclusions,indicating that the quartz secondary growth process was not accompanied by oil and gas filling.Therefore,the authors speculated that the quartz particles were cracked and dissolved after the secondary quartz enlargement.Note it.The secondary increase of quartz is related to the acidic environment,while the secondary dissolution of quartz is related to the alkaline environment.The formation of organic acid in the coal-bearing strata and the filling of oil and gas lead to the transition of the fluid environment from alkaline to acidic.Quartz secondary increased the inclusion of medium-high temperature-medium-low salinity characteristics,medium-high temperature characteristics indicate thermal fluid activity,and is related to magmatism;medium-low salinity indicates that diagenetic fluid is dominated by formation water.Both temperature and salinity have a peak,indicating that only one thermal fluid activity is experienced during the formation of quartz secondary enlargement.A few individual samples have slightly higher temperature and salinity,which may be related to external fluid charging.The laser Raman test did not detect the presence of hydrocarbon inclusions,indicating that the quartz secondary growth process was not accompanied by oil and gas filling.Therefore,the authors speculated that the quartz particles were cracked and dissolved after the secondary quartz enlargement.Note it.The secondary increase of quartz is related to the acidic environment,while the secondary dissolution of quartz is related to the alkaline environment.The formation of organic acid in the coal-bearing strata and the filling of oil and gas lead to the transition of the fluid environment from alkaline to acidic.The combination of?¹³C and?¹⁸O indicates that organic carbon is added during the diagenesis of the Xujiahe Formation sandstone,and the carbonate cement during the diagenesis may be related to the thermal decarboxylation of organic matter.The maximum precipitation temperature is 124.96°C and the minimum value is 72.62°C.It has the ability to form organic acid and carbonic acid solution,so that the minerals in the rock are dissolved to produce secondary pores.The combination of flakes to observe carbonate minerals,feldspar corrosion phenomena and clay mineral cementation all indicate the role of organic acids.At the same time,CO₂ and hydrocarbons enter the reservoir and are precipitated in the form of carbonate cement,which has certain hydrocarbon generation capacity and thus has important petroleum geological significance.