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The Baise Basin is a Paleogene pull-apart basin with numerous strike-slip faults which are not favorable for hydrocarbon preservation. The Nadu Formation, research object of this paper, is generally rich in oil and contains a large number of high-angle joint fissures. Analyzing the origin of residual oil in high-angle joint fissures can reveal the hydrocarbon migration and accumulation characteristics of the pull-apart-type basins. Molecular geochemical composition characteristics of crude oil and oil source of the Nadu Formation were discussed based on the saturated hydrocarbon biomarker compound and stable carbon isotope distribution of n-alkanes. The studied samples were selected from four members (E₂n₁, E₂n₂, E₂n_3up, and E₂n_3low) of the Nadu Formation. The results suggested that the average oil content of E₂n₁ fissures is 0.32 mg/cm², and the oil distribution is not uniform. The distribution of oil on the fissures of E₂n₂ and E₂n₃ is uniform and complete, and the oil content reaches 0.53 mg/cm². The oil in the joint fissures of the Nadu Formation is heavy, as the light hydrocarbon is seriously lost during migration. Thus, the oil in the joint fissures is residue after crude oil loses light components during migration. By comparing the molecular biomarker characteristics and stable carbon isotopic compositions, crude oil of the Nadu Formation can be classified into three categories: E₂n₁, E₂n₂ + E₂n_3up, and E₂n_3low. The E₂n₁ oils have the lowest maturity and are sourced from the E₂n₁ source rocks. Moreover, the maturity of E₂n₂ and E₂n₃ samples are relatively high. Biomarker and carbon isotope characteristics of the E₂n₂ and E₂n_3up oils are similar, indicating that they are derived from the E₂n₂ + E₂n_3up source rocks. The E₂n_3low oils are the mixture of the crude oil generated from the E₂n_3up source rocks and the E₂n_3low source rocks. Results presented show that the residual oil of high-angle joint fissures in the Nadu Formation is contributed by adjacent source rocks. The crude oil discharged from the Nadu Formation can only migrate upward along high-angle joints in a short distance, and the migration distance is usually less than 5 m. In conclusion, although the Nadu Formation has developed a large number of high-angle joint fissures, crude oil in the Nadu Formation has not vertically migrated for long distance along the joint fissures. The well-preserved fractures as important shale oil storage spaces indicate that the Nadu Formation has good shale oil exploration potential. The results may provide insights into the origins of hydrocarbons in the Nadu Formation from the Baise Basin and enhanced knowledge for optimizing future exploration and production. Full article

Drought poses a significant constraint on economic development. Drought assessment using the standardized precipitation index (S_PI) uses only precipitation data, eliminating other redundant and complex calculation processes. However, the sparse stations in southwest China and the lack of information on actual precipitation measurements make drought assessment highly dependent on satellite precipitation data whose accuracy cannot be guaranteed. Fortunately, the Chengbi River Basin in Baise City is rich in station precipitation data. In this paper, based on the evaluation of the accuracy of IMERG precipitation data, geographically weighted regression (GWR), geographic difference analysis (GDA), and cumulative distribution function (CDF) are used to fuse station precipitation data and IMERG precipitation data, and finally, the fused precipitation data with the highest accuracy are selected to evaluate the drought situation. The results indicate that the accuracy of IMERG precipitation data needs to be improved, and the quality of CDF-fused precipitation data is higher than the other two. The drought analysis indicated that the Chengbi River Basin is in a cyclical drought and flood situation, and from October to December 2014, the S_PI was basically between +1 and −1, showing a spatial pattern of slight flooding, normal conditions, and slight drought. Full article