The Exquisite Comparison of Shale Mineralogical-Geochemical Characteristics between Chang 7 Member and Chang 9 Member in Yanchang Formation, Ordos Basin

The Exquisite Comparison of Shale Mineralogical-Geochemical Characteristics between Chang 7 Member and Chang 9 Member in Yanchang Formation, Ordos Basin

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Significant amounts of unconventional oil and gas resources have been discovered in the Yanchang Formation of Ordos Basin.Shale layers deposited in Chang 7 member (divided into Chang 7-2 submember (C7-2SM) and Chang 7-3 submember (C7-3SM) and Chang 9 member (C9M)) are the main source rocks.Based on the comparison of mineralogical and geochemical characteristics, it is concluded that (1) in terms of mineralogical characteristics, the C7-3SM shale possesses Hybrid Inverter the largest content of illite/smectite mixed layer and reducing minerals and the least quantity of quartz.The C9M shale shows the highest percentage of quartz and illite and the least amount of K-feldspar and Kaolinite.

In C7-2SM and C9M shale, amorphous silica surrounded tightly by clay minerals is easily observed by the scanning Control Panel w/Keypad electron microscopy.Besides the drilling orientation, the small content of quartz contributed to the lowest porosity for the C7-3SM shale.(2) In terms of geochemical characteristics, the C7-3SM shale exhibits high productivity due to type II1 kerogen.The organic matter in the C7-2SM and C9M shale contains mainly type II2 and possibly type III kerogen.

The C9M shale exhibits the highest organic thermal maturity.The C7-3SM shale was formed in a relatively higher salinity of sedimentary water.