| The northern Guizhou area is located on the Upper Yangtze platform.Dark shale is widely developed,and the organic matter content is rich and the deposition thickness of organic shale is large,which has become the key area of shale gas exploration and development in the new stage of China.However,due to the deep buried depth and the long age of strata,the organic matter of Niulitang formation shale is too mature,which causes the reservoir properties to be different from that of Wupeng-Longmaxi formation shale in the adjacent area.According to the characteristics of high TOC,and high thickness and high maturity in the study area,this paper makes use of sedimentology,mineral petrology and reservoir geology as theoretical guidance,and makes use of regional geological report and drilling data in northern Guizhou.By sorting out and analyzing the field geological investigation report and sample analysis and laboratory data,the sedimentary facies,lithofacies paleogeography and reservoir development characteristics of Lower Cambrian shale strata in northern Guizhou are systematically studied.The sedimentary environment characteristics and reservoir development characteristics of high quality shale in northern Guizhou are pointed out.The following conclusions and understandings are being reached:The formation and distribution of source rocks depend on the sedimentary environment of sedimentary organic matter and the source of organic matter.According to the characteristics of rocks and minerals,organic geochemistry and logging curves,the sedimentary phase changes are divided into three stages.The first stage is the tectonic extension and the development of rifting,resulting in sea level rise.The rising ocean current brings rich material supply and forms a stable anoxic deep-water shelf environment.In the second stage,with the uplift of the Sichuan-Yunnan ancient continent,the sea level becomes shallow and the sedimentary environment changes to the shallow continental shelf with the slow development of the regional tectonic rifting,and the third stage tends to stop the sea level with the continuous uplift and rifting of the Sichuan-Yunnan ancient continent.Further shallower,the sedimentary facies in northern Guizhou is coastal,and sand bodies and calcareous deposits begin to appear.Through the analysis and study of sedimentary facies,the black shale of Niujiitang formation in northern Guizhou is mainly developed in anoxic deep-water shelf environment,which has the typical environmental characteristics of hot water basin formed by rising ocean current.The mineral composition of the target layer was studied by whole rock X-ray diffraction and scanning electron microscope.The results show that the spatial distribution of brittle minerals,clay materials and carbonate rocks in the shale section of Niuotang formation is quite different,in which brittle minerals(quartz feldspar)account for an average of 65% and clay minerals account for 30%.Carbonate rocks account for 5%.Through organic geochemistry analysis,the average(TOC)content of shale organic carbon in Niulitang formation is 3.5%,which belongs to the level of high quality shale organic carbon content.The main types of organic matter are II 1,and the kerogen macerals of organic matter are mainly sapropelic mud groups,which are mainly included in the analysis of organic matter kerogen macerals.The total content of amorphous and debris is above 68%,with an average of 80%.Based on the shale gas logging and drilling data in northern Guizhou,the cheese and organic carbon isotopes(? 13 C)and total organic carbon content(TOC),vitrinite reflectivity(Ro)of the collected samples were measured and compared through related experimental studies.Results the multiple data of comprehensive resource abundance,gas content,shale thickness and total organic carbon(TOC)were selected to the west of Fenggang Wuchuan and north of Weng'an Huangping as the main distribution area of high quality shale in northern Guizhou. |
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