The structural evolution and sedimentary differentiation of the Sichuan Basin in China are complex, with intricate reservoir pore structures that significantly impact shale gas production. This study examines the complexity and heterogeneity of the microscopic pore structures in the deep marine shale reservoir in the Longmaxi Formation. Pore structure characterization techniques are used to compare deep and shallow–medium marine shales, and siliceous and silty shales. The results reveal the factors influencing pore structure and their impact on exploration and development. The key points are as follows: (1) The pore structure of deep siliceous shale is the most complex due to its diverse range of pore development patterns, pore types, and sizes. (2) The box dimension of full pore size is about 1.52 for deep marine shale and 1.46 for shallow–medium shale. Organic matter (OM) content, the degree of pore development, and inorganic mineral content all correlate positively with the complexity of the pore structure in deep marine shale, which affects the formation of high-quality reservoirs. (3) Lateral heterogeneity of pore structures shows strong regional variations in the study area. Heterogeneity is more pronounced in the deep marine shale than in the medium and shallow shale formations. OM mesopores significantly influence the overall heterogeneity of the shale pore system. The deep marine shale reservoir is situated in an area with strong regional variations. The pore structure of high-quality reservoirs is more complex than those of shallow–medium marine shales, displaying notable heterogeneity. Pore structures with fractal dimension values close to that of the shallow–medium formations (box dimensions within 1.5) offer promising targets for the exploration and development of deep marine shale gas.

Shale pore systems are the result of the geological evolution of different matrix assemblages, and the composition of gas shale is considered to affect the pore systems in shale reservoirs. This study aimed to investigate the impact of both organic and inorganic constituents on the shale pore system, including specific surface area (SSA) and pore volume in Wufeng–Longmaxi Shale. Multiple linear regression (MLR) was employed to examine the contributions of different components to shale pore structure. The pore structure parameters, including pore SSA and pore volume, were obtained by gas adsorption experiments in 32 Wufeng–Longmaxi Shale (Late Ordovician–Early Silurian) samples. Both pore SSA and pore volume were calculated by the density functional theory (DFT) model on shale samples, and the pore types were determined by high-resolution field emission scanning electron microscopy (FE-SEM). The results of the X-ray diffractometer (XRD) analysis indicate that the Wufeng–Longmaxi Shale is dominated by quartz, clays, carbonates, feldspar, pyrite, and organic matter. Four models were made using SPSS software, all of which showed significant correlation between shale pore size and organic matter (OM) and clays. The content of organic matter played the biggest role in determining the size and structure of the pores. Although the content of quartz is the highest and serves as a rigid skeleton in shale reservoirs, it has complicated effects on the pore structure. In this study, most of the quartz is biogenetic and part of it is transformed from clays in deep shale. Therefore, these two parts of quartz are, respectively, related to organic matter and clays. In essence, the pores related to these two parts of quartz should be attributed to organic matter and clays, which also support the conclusion of the MLR models.

Porosity, total organic carbon content, brittle mineral content, and gas content are now the primary references for classifying and evaluating marine shale gas reservoirs in China. Is there a more effective and appropriate reservoir classification scheme for deep marine shale? The Longmaxi Formation in Luzhou, southern Sichuan Basin, China, is the main object of study. Quantitative analysis and modeling using data from field emission scanning electron microscopy, nitrogen adsorption, and logging were used to characterize organic matter (OM) pore multi-scale development and reveal the relationship between OM pore and the high-quality reservoirs. Microscopic and macroscopic indications from OM pores show that a large number of OM pores were developed in high-quality reservoirs. OM surface porosity occupancy of the high-quality reservoir in the Luzhou area was more than 60%. OM porosity occupancy was more than 50%. The nitrogen adsorption–desorption hysteresis loops demonstrate the development of bottleneck and wedge-shaped OM pores. Characterization of multi-scale pore structure by box dimension, pore volume and specific surface area. It is found that the key to the formation of high-quality reservoirs was the massive development of OM mesopores in siliceous shale and the relatively homogeneity structure, which was conducive to the enrichment and migration of shale gas. Furthermore, the improved model decreased the relative error in predicting the OM porosity by about 32.5%. The use of OM porosity occupancy for high-quality reservoir classification was better, and the results were consistent with geological understanding. OM porosity occupancy showed that the area from Lunanxi to Luzhou to Rongchang to Jiangjin was the key exploration area for high-quality reservoirs in southern Sichuan. This study is expected to provide a new idea for OM pore modeling analysis and deep marine shale gas reservoir classification.

The Paleogene Red Bed in the South Slope of the Dongying Depression is a set of red clastic sediments of the lower section of 4^th member of the Shahejie Formation and the Kongdian Formation, and is the alternative strata for oil and gas exploration in this area. The Red Bed crude oil of the South Slope of the Dongying Depression is divided into four types according to the assemblage characteristics of biomarkers from 17 oil sand samples and 3 crude oil samples. The Type I crude oil is generated from the source rocks of the lower section of 3^rd member of the Shahejie Formation, with low phytane and gammacerane concentration, Ph/ n-C₁₈0.38) and hopanes/steranes (>3.4), high diasteranes concentration, and low C₃₅ homohopane index. The Type II crude oil could be derived from the source rocks of the upper section of 4^th member of the Shahejie Formation with abnormal high phytane and gammacerane concentration, Ph/ n-C₁₈1, relatively low ratios of Ts/(Ts+Tm) (<0.38) and hopanes/steranes (<2.5), low diasteranes concentration, and high C₃₅ homohopane index. The Type III crude oil is mixed oil consisting of the Type II crude oil charged in the early stage and the Type I crude oil charged in the late stage and mainly of the Type I crude oil. The Type IV crude oil is characterized by C₂₉ sterane predominance and this feature has not been found in the crude oils and source rocks of the study area, therefore this type of oil is identified as a mixture of the Type II crude oil and an oil type from a shallow lake-swamp facies. The fault throw of oil transporting faults controls the distribution of crude oils with different genetic types, and the upthrown side of the faults is the favorable zone for the Red Bed oil and gas accumulation.

The yield of crop is low in the Northeast China because of the albic horizon. The albic horizon is characterized by high compactness, low porosity, restricts soil aeration and water circulation. As a result, these soils are difficult for crops growing. The aim of this study is to research the effects of biochar on physicochemical properties of albic horizon of albic soil and the soybean yield. The experiment was carried out in the field with albic soils. The biochar was incorporated into albic horizon to load into the bottoms of the pipes with the following ratio (biochar:albic horizon = 0.0 g · Kg^–1 (B0), 66.7 g · Kg^–1(B1), 200.0 g · Kg^–1(B3) and 333.3 g · Kg^–1(B5)). The soil of plough layer was fully mixed with fertilizers, and then the soil was loaded into the tops of the PVC pipes. The soil physicochemical properties, soybean growth parameters and yield were determined in soybean maturity period. The results showed the biochar significantly reduced the bulk density and specific gravity of albic horizon. In the other hand, it increased the total porosity, void ratio, aeration porosity, water content, total C, total N, total P, total S, total Ca, total K, C/N, available P, available K, pH_1:2,5 (H₂O), pH_1:2.5 (CaCl₂) and EC_1:5 of albic horizon. The plenty of biochar application could reduce the specific surface area (SSA) of albic horizon. Compared to B0, B3 significantly increased the soybean yield in albic soil.

The marine shale of the Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation is the main source rock and the target of shale gas exploration in the southern Sichuan Basin. The maturity of organic matter (OM) is a vital indicator for source rock evaluation. Due to the lack of vitrinite, the organic matter maturity of the Wufeng–Longmaxi Formations in the southern Sichuan Basin is difficult to accurately evaluate. In total, 33 core samples of the Wufeng–Longmaxi Formations in the southern Sichuan Basin were selected to observe the optical characteristics of solid bitumen and graptolites and measure their random reflectance. Simultaneously, Raman spectroscopic parameters of kerogen were also used to quantitatively analyze the change in maturity. By using Raman spectroscopic parameters as mediators, conversion equations between graptolite random reflectance (GR_or) and equivalent vitrinite reflectance (EqVR_o) were established. Taking the calculation results of EqVR_o as constraints, the tectono-thermal evolution history of Wufeng–Longmaxi Shale in the southern Sichuan Basin is constructed through basin modelling. The results show that the maturity of Wufeng–Longmaxi Shale in the western Changning, Luzhou-western Chongqing, eastern Changning and Weiyuan areas decreases successively. The EqVR_o falls in the ranges of 3.61%~3.91%, 2.92%~3.57%, 3.08%~3.25%, 2.41%~3.12%, and the average EqVR_o is 3.73%, 3.30%, 3.18% and 2.80%, respectively. Thermal evolution in western Changning was controlled by the thermal effect of the Emeishan mantle plume and paleo-burial depth, while the thermal evolution of other areas was mainly controlled by paleo-burial depth. This study provides a reliable parameter for the evaluation of thermal maturity and makes a more accurate calibration of the maturity of the Wufeng–Longmaxi Formations in the southern Sichuan Basin; it also expounds the factors for the differences in thermal evolution in different parts of the area.