Research On The Characteristics Of Under-salt Reservoir Of Majiagou Formation In Mid-eastern Ordos Basin

The JiXian System,The Cambrian and The Ordovician are widely distributed in the Ordos Basin. Since the discovery of weathering crust karst gas field(Jingbian gas field) in 1989, the exploration of carbonate rock oil and gas has not made substantial progress in the long-term. In recent years, oil and gas exploration in the carbonate rock regains attention in the Ordos Basin. The Mid-combination has made significant exploration breakthrough in the East of the ancient uplift(300 Billion natural gas reserves). The Su 345 well could output more than one million cubic gases daily and there are 8 wells like Su 345.In the enlightenment of The Mid- combination exploration,put forward a new knowledge is the salt rock under the coal source forlateral hydrocarbon generation and accumulation. This new understanding allows us to recognize the salt rock under the dolomite reservoir has good hydrocarbon generation conditions. Therefore, this paper relies on the project of Studying on Sedimentary Evolution and Geological Conditions of Natural Gas Accumulation in the Carbonate Rocks of Lower Palaeozoic in the Ordos Basin. The study area takes the east of under-salt basin area. Through techniques field of geological investigation, drilling core observation, thin section identification, test and analysis. Study on the system of Sedimentary facies distribution Reservoir characteristics and the development characteristics of rock salt. The related research on Controlling factors of reservoir development. Made the following conclusion:Analyzed the sedimentary evolution process and sedimentary microfacies of MaV 6- Ma-V 10 sub-sections in the mid-east of basin. The author thinks that basin from the east to the west developed supratidal doloflat face-intertidal mudflat face-gypsic saline lake in the east of the basin.The under-salt developed gray dolomite, gypsum dolomite, micrite dolomite, residual dolarenite, olitic dolomite, fine crystal dolomite and saddle dolomite through the analysis of the results of drilling core observation and indoor rock mineral identification. And the distribution and characteristics of them are studied.The good reservoir are gypsum dolomite and fine crystal dolomite and saddle dolomite.Because Majiagou formation is ancient strata, the multi-stages of tectonic movement and complex diagenesis. Based on the analysis of area of diagenetic evolution process, this paper argues that constructive diagenetic processes include dolomitization, dissolution process and degypsification; destructive diagenetic processes include compaction, pressure solution, filling, recrystallization, dedolomitisation.The system of distribution of rock salt. That change of salt rock and reservoir distribution by the influence of sea level changes, the regression period in the formation of salt rock, transgressive formation dolomite reservoir, There are four kinds of combination between the two.The development of the reservoir based on Sedimentary microfacies and dolomitization, dissolution process. Intertidal mudflat face is the favorable Micro facies. The distribution of dolomite determines the distribution of the reservoirs.