Sedimentary characteristics and controlling effect on source rocks in Wulalike Formation of Ordovician in Ordos Basin

It developes thick shale with stable distribution and it is the best source rock in Wulalike Formation of Ordovician in Ordos Basin.Many exploration wells have obtained high production of industrial oil and gas recently, it shows a good exploration situation. It has significance to study sedimentary characteristics and controlling effect on high-quality source rocks’distribution.Based on the study of sedimentary characteristics and geochemical characteristics, it shows that: ① Wulalike Formation distribute extensively and characterd by "thick in the west and thin in the east", it developes basin facies, open shelf facies and slope facies, slope facies includes upper slope subfacies and lower slope subfacies. ②It belongs to the Qilian Sea in Wulalike period, seawater is deep in the west and shallow in the east, deep in the south and shallow in the north, the slope grade is large and the facies transition is fast. ③It developes low-abundance shales in the Wulalike Formation and the spatial distribution of high-quality shales is mainly controlled by the mineral composition, sedimentary facies and sedimentary sequence. The conclusion is that open shelf facies and lower slope subfacies are favorable facies, high-quality shales are mainly distributed in the bottom 20~30 m range.