Characteristics And Main Controlling Factors Of Organic Matter Pores Of Cambrian Niutitang Formation Shale In Upper Yangtze Plate

The shale gas exploration and development of the Cambrian Niutitang Formation in the Upper Yangtze plate is relatively poor,and there are obvious differences in the development of organic matter pores in different areas.In this paper,samples were collected from shale Wells located in three different depositional locations: EYY1 Well in the east of the Upper Yangtze Plate,W001-4 Well in the north and SNY1 Well in the west.According to the existing data and previous research results,the lithofacies were divided according to the XRD test results,and the types of organic matter and the development characteristics of organic pores and inorganic pores were analyzed and studied through scanning electron microscope observation and low-temperature nitrogen adsorption test.On this basis,the main controlling factors of organic matter pore development are analyzed and discussed,which provides an important reference for the exploration and development of Cambrian shale in the study area.The study shows:(1)The main minerals of Niutitang Formation shale in the study area include quartz,feldspar,calcite,dolomite,clay minerals and a small amount of pyrite and siderite,etc.;According to the mineral composition of shale,the shale lithofacies of EYY1 Well and W001-4 Well can be divided into three types: siliceous shale,calcareous shale and transitional shale,and the shale of SNY1 Well is all siliceous shale;(2)The organic matter of the three Wells in the study area is mainly ? type kerogen.The organic matter was divided into depositional organic matter and migrated organic matter according to morphology and energy spectrum.The C/O values of the depositional organic matter in the three Wells were high,with an average of 6.74.On the contrary,the value of C/O of the migrated organic matter is relatively low,averaging 2.71;(3)The shale of Niutitang Formation in the study area is dominated by micropores and mesopores.There are three types of pore size distribution patterns in well EYY1Well: mesoporous+microporous dominant type,mesoporous dominant type and micropore dominant type.The pore size distribution pattern of well W001-4 is dominated by micropores,followed by mesopores.The pore size distribution of SNY1 Well is dominated by micropores;(4)The organic matter pores in EYY1 Well and SNY1 Well are well developed with relatively high facial ratio,while the organic pores in W001-4 Well are poorly developed.The organic pore diameter distribution of the three Wells was single peak type.The organic matter pore diameter of EYY1 Well and SNY1 Well is mainly distributed in the range of 2-50 nm,and the organic matter pore size of the samples from W001-4 Well is generally between 5nm and 25 nm.(5)The pore development of organic matter in the Niutitang Formation shale in the study area is affected by many factors.The pores of the migrated organic matter are better developed than tdepositional organic matter.The effect of organic matter's hydrocarbon generation and pore enhancement and compaction and reduction of pores are superimposed on the development of organic pores.Felsic minerals and clay minerals are important factors for the pore development of organic matter in shale,and clay-rich siliceous shale may be an important clue for the selection of dessert in Cambrian shale gas.