Coupling relationship between sedimentation of favorable intervals and lake level change and its controlling factors in lacustrine tight reservoir: A case study of the Lower Shangganchaigou Formation in the Gasi area, western Qaidam Basin, China

Exploring the relationship between favorable sedimentary intervals and the change of lake level can provide some reference for the exploration and development deployment of the lake-phase dense reservoir. In this study, taking the Oligocene Lower Shangganchaigou Formation in the Gasi area of the western Qaidam Basin as an example, Fischer diagrams and U-TOC regression fitting method were used to reconstruct the process of lake level change during the Oligocene sedimentary period using Natural gamma ray (GR) curve data, and the climate controlling factors of lake level change were discussed in combination with magnetic susceptibility data. The results show that: (1) The Fischer diagram of Lower Shangganchaigou Formation in the Gasi area is consistent with the trends of mud content and TOC content, all reflecting that it has undergone two lake retreat and lake advance processes during deposition, which are favorable for the formation of source rocks and reservoirs; (2) The high water level sedimentary system formed during the lacustrine rising period corresponds to the enrichment intervals of high-quality source rocks in tight sandstone reservoirs, which can effectively form a source-reservoir symbiotic configuration; (3) The change of lake level in the Oligocene was controlled by the climate under the westerly wind condition. The water vapor brought by the westerly wind formed relatively humid climate conditions and caused the rise of lake level, which was favorable for the formation of source rocks and presented a coupling relationship with the deposition of favorable intervals.