Study Of Dolomite Genesis And Diagenesis System Of Huanglong Formation Of Carboniferous In Eastern Sichuan-Northern Chongqing Area

Dolomite genesis problem is one of the most complex,disputing and difficultly resolving carbonate petrology difficulty,and diagenesis system study is a new frontier field combined with Sedimentary Basin Dynamics during developing diagenesis study. By the complex reconstruction of the penecontemporaneous pore water diagenetic stage,atmospheric water diagenesis system at ancient epigenenesis,early diagenetic burial stage of compaction brine diagenesis system and the middle to late re-buried temperature and pressure water diagenetic stage in eastern Sichuan-northern Chongqing area,carbonate of Huanglong Formation ultimately form carbonate reservoir which included three main rock types of grain dolomite ,crystalline doloston and corrosion-brecciated of karst rock. Dolomite genesis and Hydrological system are the key of evaluating carbonate reservoir of Huanglong Formation. So,the study of dolomite genesis and diagenesis system of Huanglong Formation reservoir not only important for theory significance, but also for practice significance.Based on the new conclusion of inland and overseas , and combined with the palaeogeographical setting of the study area,used instrumentations of lithology-mineral identification techniques;Carbon,Oxygen ,strontium stable isotopes;trace elements;rare earth elements and inclusion,by study of Dolomite genesis and diagenesis system and there relations with reservoir of Huanglong Formation ,the may conclusions and new recognitions as follows:1. Through comprehensive analysis of field section, well core description and lithology-mineral in house,dolomite styles of dolomicrite,crystal powder-fine dolomite, grain dolomite , corrosion-brecciated of karst rock , the fresh water dolomization , hydrothermal dolomization have been recognized. By classify with composition-genesis,the four models of dolomization have been set up:the penecontemporaneous dolomization,the burial diagenetic dolomization , the fresh water dolomization of epidiagenesis and hydrothermal dolomization of late diagenetic stage. Dolomite with different stages and genesis have the evolutionary trend of strengthen by diagenesis intensity,dolomite degree of order get higher,MgCO3/CaCO3 ratio arise trend of 1. 2. Through the characteristics of sequence-based lithofacies and paleogeography,sabkha facie which developed on period of The low system tract sequence,the evaporation environment which developed on period of episodic regression stage of transgression system tract in limitate area,and layer brine water which seal up in this environment offer fluid original source material condition for early diagenetic stage burial dolomitization . The barrier grain beach and offshore grain beach in TST period are the most active area of the early burial diagenetic,And are thought the most favourite reservoir facies.3. Based on the characteristics of Carbon,Oxygen stable isotopes, the diagenetic burial dolomitizing fluids came from burial brine water of early stage sabkha environment,the genesis of karstification of epidiagenetic stage and limnic-dolomite and limnic-Calcite have related with atmospheric water corrosion,hydrothermal dolomite of reburial period is the precipitate of deep hydrothermal fluid corroded dolomitic matrix rock.4. By the synthetical analysis of geochemical characteristics of Sr isotope,further demonstrate that the diagenetic burial dolomitizing fluids came from sea origin brine water of Huanglong Formationâ… , fluids of karstification of karst rocks and the cement of limnic-dolomite and limnic-Calcite came from atmospheric water of epidiagenetic stage,and hydrothermal dolomite is the result of deep hydrothermal fluid participated in diagenesis.5. By the synthetical analysis of geochemical characteristics of rare earth elements,the conclusion that the removing of the REE at dolomitization process strongly in the penecontemporaneous stage and diagenetic burial stage,the diagenetic burial dolomitizing fluids came from brine water of penecontemporaneous stage,karstification of karst rocks and the cement of limnic-dolomite and limnic-Calcite take shape from weak oxygenated low temperature atmospheric water fluids. Rare earth elements characteristics of hydrothermal dolomite reflected it's the hydrotherm mineral of hydrothermal fluid corroded matrix dolomite rock on reburial period.6. According to geochemical behavior and diagenetic fluid property of different genetic types dolomite,though"Hydrological system"and the manner of diagenesis,researching of corresponding product of geology,combination,evolution stage of diagenesis in Huanglong Formation are divided into four fuild origin,property,water-rock interaction process,the effect of them to the reservoir development are also different. So the diagenesis systems and manner of diagenesis,are mainly as follows:the penecontemporaneous stage pore water diagenesis system;early diagenetic burial stage of compaction brine diagenesis system;ancient epigenenesis atmospheric water diagenesis system at and re-buried deep temperature and pressure water diagenetic stage.7. Discussed the relations of the diagenesis systems and reservoir development, which related to the reservoir development closely,are mainly as follows:the role of burial dolomitization of compaction brine diagenesis system at early diagenetic stage ; the karstification of atmospheric water diagenesis system at ancient epigenenesis; the role of tectonic disruption at the middle to late re-buried diagenetic stage.