This study examines the effect of fault sealing on hydrocarbon accumulation in the Xihu Sag where NE- and NNE-striking faults within the sag prevent the escape of trapped oil and gas. Analyses like the shale gouge ratio (SGR), shale smear factor (SSF), and fault lateral sealing coefficient (F_h) are used for a quantitative evaluation of the lateral sealing capacity of faults in the Yuquan area of the Xihu Sag. Paleo-structural sections reconstructed using cross-section balancing techniques are used to analyze the evolutionary characteristics of fault sealing. The results indicate that the lateral sealing capacity of faults is mainly controlled by fault throw, clay content, and sand–shale distribution characteristics; in the Yuquan area, fault segments exhibit good lateral sealing when the SGR exceeds 0.5, the SSF is less than 2.5, and the F_h is greater than 10.5. The methodology for evaluating fault sealing evolution, established using structural reconstructions during key geological periods, shows that fault sealing capacity increased gradually over time; in the Xihu Sag, effective sealing of the main hydrocarbon-bearing intervals began during the Liulang period. Evaluating fault sealing capacity is also crucial for estimating the rate of hydrocarbon accumulation, and typically shows a positive correlation with gas (oil) column height. In the Yuquan area, the volume of hydrocarbons sealed by the faults increased progressively over time, with a relatively high overall fault sealing capacity during the second hydrocarbon accumulation period. This study provides valuable insights into the evaluation of fault sealing capacity as well as an investigation of the relationship between faults and hydrocarbon migration–accumulation in the Xihu Sag and analogous geological settings.

Restoration of denudation thickness is of great significance to understanding tectonic evolution, hydrocarbon migration and accumulation history in petroliferous basins. How to accurately restore and distinguish denudation thicknesses in different periods, however, is difficult. With measurements of vitrinite reflectance (R_o) and interval transit time, along with stratigraphic profile comparison, we restored the total denudation thickness of the Cretaceous in the central Sichuan Basin at a depth range of 1100–3300 m. The apatite fission track analysis (AFTA) was employed to identify the denudation periods, namely, the Late Yanshanian, Early Himalayan and the Late Himalayan orogenic epochs, and the ratio of their denudation intensity is about 3.8:1:3.9. The denudation thicknesses at different periods provide an important basis for tectonic evolution and hydrocarbon migration and accumulation. Affected by the diverse denudation intensities, the paleo-structures in the study area feature high in the south and low in the north at the Late Jurassic, high in the north and low in the south at the late Early Cretaceous, high in the southeast and low in the northwest at present in succession. EW- and NE-trending folds and faults are the products of inherited development, which have a controlling effect on hydrocarbon migration and accumulation.

The hydrocarbon transport effectiveness along faults is a key factor influencing hydrocarbon accumulation and enrichment in moderately shallow reservoirs. Assessing this factor holds great significance for the emplacement of hydrocarbon exploratory wells in medium-shallow reservoirs in the central Sichuan Basin. This study focuses on the Shaximiao Formation in the central Sichuan Basin. Following the analysis of fault distributions and origins, we assess the gas transport capacity of source rock-rooted faults, investigate the fault-sand configuration and its evolution, and reveal the controlling effects of fault-sand configuration on the migration and differential enrichment of gas, based on fault activity rates, compressive stress directions, and normal stress on fault plane. The results indicate that the reverse and normal faults cutting through the Upper Triassic Xujiahe Formation and the Lower Jurassic source rocks in the central Sichuan Basin serve as the source rock-rooted faults of the Shaximiao Formation. The reverse faults, among others, are governed by the tectonic compression in different tectonic movement periods, whereas the normal faults are formed due to the differential subsidence with uplifting and sagging in a weak extensional setting during the early to middle sedimentary stages of the Shaximiao Formation. The reverse faults, Longquanshan, Jiao-1, and Jianyang-1, as well as normal faults in the central Sichuan Basin exhibit high transport capacity during the Late Yanshanian and the Late Himalayan. Considering factors such as fault size and the hydrocarbon generation intensity of underlying gas sources, it can be inferred that the Longquanshan and Jiao-1 faults play the most significant role in hydrocarbon transport. The source rock-rooted faults in the central Sichuan Basin are mostly of the inherited type, conducive to the continuous gas charge into favorable sand bodies in different charging periods. In contrast, the Jiao-1 fault is of the inverted type, exhibiting different gas charge directions in the early and late stages and allowing for natural gas charge on both sides. Major factors governing the differences in natural gas enrichment include the size of source rock-rooted faults, fault-sand configuration, and the hydrocarbon generation intensity of source rocks.