Study progress of origin of fine-grained sedimentary rocks in deep-water area of lacustrine basin: Taking Yangchang Formation in Ordos Basin as an example

Since the exploration objects gradually changed from shallow-water to deep-water area in lacustrine basins for China's Meso-Cenozoic lacustrine basins, it will break the concept that the deep-water area is a forbidden zone for hydrocarbon exploration. Fine-grained deposits in the deep-water area were poorly studied in the past, and mainly focusing on the hydrocarbon-generating potential of source rocks. In order to determine the types and origins of the fine-grained deposits in the deep-water area, and to guide unconventional hydrocarbon explorations, a case study was made in the Yanchang Formation of the Ordos Basin. Based on a large amount of previous data and combined with modern testing techniques, the sedimentary facies and origins of rocks in the deep-water area were analyzed, especially the characteristics and origins of deep-water autochthonous sedimentation, tuff, deep thermal fluid, distal turbidite and radioactive uranium. It was emphasized that rock and mineral analysis together with geochemical analysis were the main methods to realize fine-grained deposits, among which nanotechnology would be the main research method in current and the future. A certain amount of pores developed in the fine-grained deposits in the deep-water area, which were close to source rocks, hence were favorable for hydrocarbon accumulation and exploration.