Reservoir Characteristics Of The Ma5 Setion Of Ordovician In Western Sulige Gas Feild

The Ma5 setion of Ordovician is the most importaint producing reservoirs in the east Sulige Gas Field, Ordos Basin. It is very important to researeh on reservoir characteristic in order to explore and develop natural gas in this area. The researeh object of this paper is Ma5 section of east Slige Gas Field. Based on previous study,and guided by the theory of sedimentology and reservoir geology, author elaborated the sedimentary microfacies, diagenesis, and reservoir characteristic ect. in this paper, by detailed describing the core 18 wells, identifying rock thin section, cathodoluminescence, SEM obseevation, mercury intrusion analysis, logging, database of core porosity and permeability, ect. There are five views are achieved in this study as following:First, according to core descriptions and thin section identifications, there are 10 Lithology-Micro-Phase association: mud- crystallite dolomite,crystallite- powder crystal dolomite,crystallite- powder crystal limestone dolomite,powder crystal-aplitic dolomite limestone,mud- crystallite limestone,mud limestone,mud dolomite,gpsum,gypsum breccia and gypsum dolomite.Secondly, abundant thin section identification, core ananlasis combining the Gas Field reseach data predicts that the main diagenesis in Ma5 section includes dolomitization, compaction, pressure solution ,recrystallization, dissolution, degypsumization,dedolomitization and pyritization. Supergene dissolution phase take a vital importance in M1—4 section reservoir producing, while penecontemporaneous dolomitization just promote the proceeding without the production of advantage porosity; Compaction and pressure solution are all hurmfull to the reservoir development. Thirdly, porosity in M5 section include intraerystalline pore,birdeye pore,gypsum mould pore,intererystalline solution pore,solution pore and dissolution fractures ect. Among them, intererystalline solution pore and dissolution pore are the main reservoir space. Generally statement indicate that in certain depositional environment, crystal powder dolomite and anhydrite containing nodule or columnar crystal crystal powder dolomite are the material base for reservoir development, while the development and Preservation of secondary pore s, cracks and holes formed in Supergene diagenesis and buried diagenesis phase will be the key part in the good reservoir formation, and also the later structural fracture further perfect the reservoir permeability system.Fourthly, sub layer M5₁³ and M5₄¹ reservoir comparatively good,so as the physical property and gas content, and porosity,permeability and gas content degree of saturation own a well correlationship, among them, porosity and permeability present obvious positive correlation. Reservoir anisotropism totally shows that hyposmosis areas partly own middle and high permeability wells, with obvious difference between layers. Statistic analysis shows that high-yield wells are mostly from sub layer M5₁³ and M5₄¹, besides which own few.Fively, on the basis of sedimentary facies, diagenesis, porosity, and reservoir physical property, this thesis make a reservoir valuation, and also divides the reservoir into four: classⅠ,classeⅡ,classⅢand classⅣ. Then the fine reservoir areas are described.