Cover Story
Middle Jurassic Buqu Formation (J2b) oolitic lime-stone from Well Qs1 in Shenglihe area, North Qiang-tang Depression. Well Qs1 is a geological survey well with a depth of 500 m located in the upper reaches of Shenglihe in North Qiangtang Depression in 2022. Liquid crude oil was discovered in the core of this well, and it is of great significance for promoting oil and gas exploration in the Qiangtang Basin. This gray oolitic limestone is stratigraphically located at the bottom of the Middle Jurassic Buqu Formation, which is a key horizon for the development of source rocks; in terms of sequence, it is located at the bottom of the rising half cycle (TSTb1) of the third-order sequence SQb1; in terms of sedimentary facies, it is in the oolitic shoal microfacies of the foreshore subfacies of the mixed sedimentary shoreface facies. From thin secton observation under the microscopic, it can be seen that the oolite content is as high as 80%, with a size of approximately 0.4 mm. Simultaneously, frac-tures developed, and the spaces between the oolites and the fractures were filled with microcrystalline and spar calcite. For details see pp. 561-576 of this issue. (Photo by WANG Qian).
