The Study Of Dolomite Genesis And Diagenisis System Of Majiagou Formation Aroud Paleo-uplift,ordos

The fact of Chinese oil-gas exploration tells that the formation of four Carbonate quality reservoirs ,who are paleokarst reef bank and dolomite,has intimate relationship with dolomitisation,except for paleokarst,so dolomitisation is the key problem of the Carbonate quality reservoir research.Dolomite problem is the constancy debate of sedimentology,the research of fluid and diagenesis system is the hot of diagenesis in recent years and the research of diagenesis process is favour of hunting better reservoir area,which also is the puzzle of carbonate reservoir predication. Based on predecessors researches,using obserbation of slice &SEM and X-ray;trace elements; REE; Carbon,Oxygen,Strontium stable isotopes;enclosure and cathodoluminescence test techniques ,by studying Dolomite genesis and diagenisis system of Majiagou Formation,the may conclusions and new recognitions as follows:(1)Sedimentary systems around the paleo-uplift are analyzed detailedly, sequence-based lithofacies-paleogeographies are compiled taking sequence tract as element,which reproduce the sedimentary evolution of Majiagou Formation,and the differences of sedimentary system are as follow:the southwest is epicontinental sea carbonate platform,while the east is continental sea carbonate platform,at the same time,their model are established.(2) By classifying dolomite with composition-genesis,the degree of order of microlite dolomite is low,while the crystalline dolomite is high.Trace elements tell that dolomitisation of microlite dolomite is high saline sea water in open system,whereas crystalline dolomite is fluid from sea water in close system.(3) REE demonstrates that dolomitisation fluid of two kinds of dolomite comes from sea water and dolomitisation is the process of REE losing. microlite dolomite is formed in weak oxidation/reduction environment,while crystalline dolomite,which is maybe reformed by oxydation hydrothermal fluid,is formed in higher temperature than microlite dolomite.(4)The character of Carbon,Oxygen stable isotopes shows dolomitisation fluid of both microlite and crystalline dolomite is sea water or come from sea water, fresh water maybe taked in the dolomitisation of the former,while the latter formed in buried condition.(5)The homogenization temperature which has modified reveal that microlite dolomite formed near surface wheas crystalline dolomite formed during high temperature.Both of two kinds of dolomite show weak ro middle hyacinth light,which tells the fluid come from sea water.(6)Based on the comprehensive analysis of lithlogy and geochemistry,the diagenesis of Majiagou Formation include dolomitisation cementation compation&pressolution recrystallization gypsification karst degypsification and dedolomitisation,seven diagenensis facices are divided according to special diagenesis and main rock.(7)After the analysis of lithlogy geochemistry and diagenesis,according to characters of"Hydrological system",four diagenesis systems,which are high saline sea water enveloped bittern fresh water and ramming warm water,whose fluid feature water-rock process diagenesis mode and geochemistry are different are divided.The karst of fresh water and embedding dolomitisation burying karst of ramming warm water are benefitted to forming quality reservoir of Majiagou Formation.