Study On Characteristics And Mechanism Of Ordovician Weathering Crust Reservoir Of Tabamiao Region

Based on the application of theories new methords and technologies combined with geological and testing data, the theses mainly deals with the distribution and reservoir mechanics of carbonate rock subtle oil and gas reservoir in Ordos basin, which is developed by the weathering of carbonate during late Ordovician. Synthetically study achievements have been made as follows:1. Constructive diagenesis consists of karstification, replacement, dissolution and recrystallization for the Ordovician carbonate rocks. Secondary porosity formed in two stages, first stage occurred during the penecontemporaneous and epigenesis, when the large number of solution cavity, fractures and solution pores developed; the second stage occurred during late diagenesis, the fine crystalline dolostone reservoir fomed. The formation of intercrystalline pores is due to the hydrothermal water disslution. M₅⁵ fine crystalline dolostone reservoir is firstly recognized in this study. The dickite recognized by SEM contributed lots to the late diagenetic dolostone reservoir.2. Infiltration is the main factor which sharply reduces the space of karst reservoir. The second important discover in this study is that large cavity infiltrated by dark mud and clast of carbide plant in well 32. That shows the strong karstification indicating the existence of cavity forming conditions. Chemical infiltration includes fresh water calcite, hydrothermal material and bitumen. Cavity and dissolution infiltration developed earlier than the infiltration of authigenic minerals and bitumen.