The Calcite Elements And Fluid Characteristics Of The Hole In The Lianglitage Formation Of Upper Ordovician In Tazhong Area

Thermal fluids are widely used for deep to ultra-deep carbonate rocks transforming,and the research has been deepening.However,the cementation process and fluid environment evolution after multi-period superimposed and thermal fluids transformed are yet to be further studied.In this study,two wells near the major faults of south and north in the Tazhong area were selected,aiming at the multi-phase calcite cement in carbonate cave,using a combination of hand-specimen observation,microscopic identification,fluid inclusion testing,cathode luminescence,and LA-ICP-MS analysis,to comprehensively studying the elemental composition,fluid environment characteristics,and evolution of different phases of cement in carbonate dissolution pores.The main conclusions are as follows:(1)Through core observation,thin section identification,and cathode luminescence,cement phrases in carbonate dissolution pores were divided,including fiber-column calcite cement and granular calcite cement(according to the crystal size can be further divided into two phrases).(2)The characteristics of fluid environment in different cements were studied.The fiber-column calcite cement in Zhong 2 well has high salinity and no cathode luminescence.The smaller-crystal granular calcite cement has the characteristics of medium temperature and salinity with relatively strong cathode luminescence,while the bigger-crystal granular calcite cement are dominated by high temperature and salinity with relatively weak cathode luminescence.(3)Explore the source characteristics of different cement fluids.Different phases of cement are obviously affected by thermal fluid,formation water and atmospheric fresh water.Granular calcite cement is divided into two fluids environment: mixing thermal fluid and formation water,mixing thermal fluid and atmospheric fresh water.The fiber-column calcite cement diagenetic fluid environment may be the cause of the transformation of formation water by thermal fluids and the intense transformation of atmospheric freshwater.The Shunliu 6 well closer to the top of Lianglitagezu may have recorded the influence of atmospheric fresh water reconstruction.Still,the injection period of atmospheric fresh water and the environment of element evolution in different cements need to be further studied.