A Study On The Characteristics Of Ordovician Source Rocks And Reservoirs And Cap Rocks On The West Margin Of The Ordos Basin

The western margin of the Ordos Basin situates in the integration area of the two tectonic domains between the eastern and western parts of China,and it is very complicated for the tectonic evolution。It is characterized by the presence of well-developed marine deposits of Ordovician。The geochemical characteristics and log response characteristics of source rocks in different strata of Ordovician are obviously diverse by reason of the factors of structure activity and sedimentary environment。The reservoirs and caprocks and their combination modes have obvious characteristics。Means and theories of petroleum geology,sedimentology,geophysics and petrology and date of outcrop,drilling cores,drillings,loggings and inside jobs are integrated to study characteristics of source rocks,reservoirs and cap rocks of the western margin of the Ordos Basin。The organic matter types of Ordovician in the western margin of Ordos Basin belong to typeâ… andâ…¡₁。The hydrocarbon source matter is correspondingly good。The source rocks of the Wulalike Formation has maximum abundance of organic matter in the study area。The abundance of organic matter of Ordovician carbonate increases with the augment of shale content。There are the high matured-over-matured source rocks in the study area on the whole,but immature to mature organic matter of Middle Ordovician exist in Pingliang Area of Gansu and some well blocks。There are differences for logging curves characteristics of source rocks and their upper-lower stratum。The natural gamma ray curves show high value that increases with the augment of abundance of organic matter in general。Other logging curves show respective logging characteristics。The secondary dissolution pores are main types in reservoir space of carbonate reservoirs in the study area。The fractures develop because of the impact of tectonic stress field。Dolomite intracrystalline pore reservoir and dolomite intracrystalline pore-karst reservoir and weathered crust reservoir are the main carboniferous reservoir types。The west side and the northern section of Tianhuan Depression are the favorable exploration area of the Ordovician reservoirs in the western margin of Ordos Basin.Mudstone of Yanghugou Formation and Taiyuan Formation in Carboniferous—Permian and the dark mudshales of Pingliang Formation of the Middle Ordocivian are considered as good regional caprock in the study area。Dense carbonate reservoirs which don't develope pore and fractures in Zhuozishan Formation and Kelimoli Formation may be used as the regional caprocks of Ordovician.Paleo-weathering crust reservoir-caprock combinations and insider reservoir-caprock associations of Ordovician which may be oil and gas exploration in the western margin in Ordos Basin are significant reservoir-caprock associations。...