Research On Taiyuan Formation-Shanxi Formation Sedimentary Facies And Potential Shale Gas Exploration

Ordos Basin is one of the most important large sea-land transitional sedimentary basins of China.In recent years,Sulige,Yulin and other large Paleozoic gas field had been found in the north of the Ordos Basin with the deepen efforts to exploration and development of natural gas of China,but the research on the Upper Paleozoic strata of Ordos Basin are still in a weak state,and the past research mainly focused on conventional oil and gas resources and coal-bed methane,which greatly restricted the exploration and development of shale gas of the Ordos Basin.Based on the sedimentology and the hydrocarbon generation theory of the source rocks,the formation environment and accumulation characteristics of the Taiyuan and Shanxi groups shale reservoirs are proposed of the Ordos Basin.Taiyuan Formation and Shanxi Formation are the mainly mud shale strata of the Upper Paleozoic of the Ordos Basin.Based on the measured profile and the collected drilling column of the study area,the Sedimentary facies of the Taiyuan Formation and Shanxi Formation of the study area were identified.There are five sedimentary facies include fluvial facies,lake facies,delta facies,barrier coastal facies,shallow sea continental shelf and 8 subfacies include overbank subfacies,shallow lake subfacies,delta plain subfacies,delta front subfacies,barrier island subfacies,lagoon subfacies,tidal flat subfacies,carbonate platform subfaciess.The shale shale is widely distributed in the study area,and the two sedimentary centers Yonghe and Huanxian are the most thick area of Taiyuan Formation,while lake are the sedimentary centers of the Shanxi-2 Formation and the Shanxi-1 Formation.The soil organic matter abundance(TOC)in the study area is very high in genearl.and more the 75% the sample are upper 1%.The results of the element analysis of the mud shale sample show that the type of kerogen of the study area are mainly?1type(humic sapropel type)and?2 type(saprophytic humic type)and a small amount of type ?,which have a good potential ability of gas generation.The vitrinite reflectance(Ro)of the organic matter in the Taiyuan and Shanxi strata of the Ordos Basin is between 0.8% ~ 2.0%,most of them are in the high mature stage.The X-ray diffraction analysis of the samples of the study area shows that the mud shale in Taiyuan and Shanxi groups is mainly composed of clay minerals such as montmorillonite,illite and chlorite,and brittle minerals such as quartz and feldspar.The mud shale of the study area has a high degree of pore development and high connectivity,and it can be a good reservoir for shale gas.The mud shale development regularity is summarized through the research on its organic matter content,maturation,organic matter types and its porosity,permeability and sedimentary facies,at the same time,the favorable area of the Ordos basin had been chosen and the research provides a theoretical basis for the development of the Paleozoic shale gas of the Ordos Basin.