Research on the Sedimentary Microfacies and Diageneses of Ma5 1-4 Submember in Jingbian Gas Field

Key words: 
• Jingbian Gas Field /
• Ma51-4 submember /
• sedimentary microfacies /
• diagenesis

Abstract: Majiagou Formation of the middle part of Ordos Basin belong to epeiric sea carbonatites and evaporates. Majiagou Formation have Ma1 Ma6 Member(from bottom to top), Ma1, Ma3, Ma5 Members are micritefine powder dolomite, gyprock and saline. Ma2, Ma4, Ma6 Members are mainly micrite limestone or wackestone. Caledonian event uplift North China Platform since last stage of Middle Ordovician. The top of Majiagou Formation in Ordos Basin udergo weather worn in 1300 million endurance. Weathered crust dolomite reservoir of the top of Ma5 Member are produced by dissolution of ancient karst. Ma5 member divided into Ma510, Ma59…Ma51 from bottom to top. The producing pay allocation in Ma51－4〗submember which are top of weather crust. Ma514 submember have thick 80~110 m, are dolomite, argillaceous dolomite, minor gypseous dolomite andtuffaceous mudstone. The reservoir rock of Ma514 submember are mainly corrosion pore and hole dolomite, valid reservoir are grand total 2~10 m, which initial rock are gypseous micritefine powder dolomite. 
Ma 51－4 submember of Jinbian Gas Field in Ordos Basin belong to evaporated carbonate tidal flat facies,which divided into three subfacies: supratital zone, intertital zone,infratital zone, and 18 microfacies. The microfacies that are favour of developing reservoirs are supratidal zone dolomite which have anhydrite noddle and upper part intertidal zone dolomite which have anhydrite crystal. Ma514 Submember had undergone various diageneses. Penecontemporaneous dolomitization and gypsification that settled material base of reservoirs. Epidiagenesis selective dissolution of gypseous dolomite constructs the ambit of reservoirs. anhydrite noddle and crystal in dolomite selectively dissolved by meteoric fresh water and create pore and hole. Dissolved pore and hole what partly fill by one or some mineral form reservoirs. Early stage dissolution pore and hole are reconstructed by burial period dissolution, fill mineral sort and amount that determine the preservation condition of dissolution pore and the feature of reservoirs. 
Call in “minus cement porosity”, it directly reflects sedimentary that control reservoir Ma514 Submember. Combining of research microfacies and diagenesis facies, use concise numerical symbol that express semiquantitatively sedimentary microfacies and diagenesis facies. Used that in compilation microfacies chart and diagenesis partition chart, beneficial area for reservoir is so clearly. That method acquire approved effect on the evaluation and forecasing reservoir of Jingbian Gas Field.