For the second member of the Permian Lucaogou Formation in Malang Sag, Santanghu Basin, we used field emission scanning electron microscopy (SEM), cryogenic nitrogen gas adsorption, and the micro/nano CT method, combined with the fractal theory, to depict the dense reservoir space types of the reservoir and the microcosmic pore structure characteristics, perform the quantitative evaluation of aperture size, pore shape, and connectivity, and to analyze the mineral composition of the micropore structure of the reservoir. The results show that the area is dominated by sandy/argillaceous dolomite, and the reservoir space types mainly develop dissolved intergranular pores and intergranular pores, a few microfractures, and parallel plate and slit nanoscale pores. There is a positive correlation between pore volume and specific surface area, with micropore volume accounting for 14.95%, mesopore volume at 82.47%, and macropore volume at 2.58%. The mesoporous volume provides the main pore storage space. The combined specific surface area of micropores and mesoporous pores accounts for more than 99% of the total specific surface area, providing almost all the pore surface area, which is the main site for shale oil and gas adsorption. The fractal dimension D value of the samples is between 2.39 and 2.49, and the pore distribution of shale is relatively uniform, mainly developing mesoporous pores. The specific surface area and average radius are positively correlated with the content of dolomite in mineral components. The results of the CT experiment also confirm that the pore throat of samples with high dolomite content is mostly a coarse tubular and banded distribution in three-dimensional space, with good connectivity.

Wufeng–Longmaxi Formation and Qiongzhusi Formation are the significant shale gas exploration strata in China. The former has made a major breakthrough, and the exploration of the latter is restricted. At present, it shows good exploration potential in the Qiongzhusi Formation. Based on the field outcrop and core logging data, the production data from drilled shale gas wells and previous research results combined with the determination of organic matter content, laser Raman spectroscopy of organic matter, X‐ray diffraction experiments, and field emission scanning electron microscopy observations. This study compares the geological conditions and control factors of shale gas enrichment and high yield in the Wufeng–Longmaxi Formation and Qiongzhusi Formation and clarifies the enrichment mode of two sets of shale gas reservoirs. The results show that the organic geochemical conditions of two sets of shale reservoirs are similar, about 0.5%~4.5%. The quartz content of Wufeng–Longmaxi Formation shale (42.5%) is more than that of Qiongzhusi Formation (34.1%~40.2%), and the feldspar content (6.4%) is less than that of Qiongzhusi Formation (20.5~27.3%). The inorganic pores of the Qiongzhusi Formation are more developed than those of the Wufeng–Longmaxi Formation, and the pore size of inorganic pores can reach 100 nm~1 μm. Both of them have good preservation conditions. The enrichment of shale gas in the Wufeng–Longmaxi Formation is controlled by hydrocarbon generation reservoir‐preservation conditions, and the enrichment of shale gas in the Qiongzhusi Formation is mainly controlled by geological structure. It is of great significance to clarify the enrichment control factors of the Qiongzhusi Formation for effectively guiding the continuous exploration and development of the Qiongzhusi Formation. Shale gas exploration in the Qiongzhusi Formation has a very large prospect, which is expected to exceed the Longmaxi Formation.

The organic-rich shale of the Wufeng-Longmaxi formation is an important section for shale gas exploration. The traditional univariate or bivariate analysis causes researchers to have great controversy about its enrichment mechanism. This study explores the combination of multiple factor analysis (MFA) and element geochemistry to calculate the contribution rate of a paleoenvironment to organic matter enrichment and clarify the main controlling factors of organic matter enrichment. Research has shown that there is generally high productivity from the Wufeng (O(3)w)-Longmaxi formation (S(1)l) deposition. The degree of terrigenous clastic input and weathering during the period of the O(3)w is relatively low, and sedimentary water restriction is strong, mainly developing an anoxic-dysoxic sedimentary environment. During the deposition of S(1)l(1), the input intensity and weathering of terrigenous debris were slightly enhanced, and the increase of the water column led to the development of an anoxic environment at the bottom of the water layer. During the S(1)l(2+3) period, the degree of terrigenous debris and weathering is the largest, and the high oxygen content of the water column is mainly a normal oxic environment. An MFA calculation shows that the paleoproductivity and paleoredox environment of the organic-rich shale section have the highest contribution rate of about 59.57% to the enrichment of organic matter, which is higher than that of paleoclimate conditions and terrigenous clastic input, indicating that the enrichment of organic matter is mainly controlled by paleoproductivity and the preservation environment. This study provides a basis for the application of MFA in element geochemistry and can serve as a model for other studies.