In order to quantitatively characterize shale pores and microfractures, twelve marine shale samples from the Longmaxi Formation in the southeastern Sichuan Basin were selected and their NMR T₂ spectra were analyzed under the conditions of full brine saturation, cyclic centrifugal treatment and cyclic heat treatment. Then, movable, capillary bound and unrecoverable fluid of shale samples were distinguished and the NMR porosity and full-scale PSD were calculated. Based on NMR spectral peak identification, the relative content of pores and microfractures was determined and their influence factors were analyzed. The results show that the PSD of shale samples is bimodal, with pores distributed in the range of 1 nm to 200 nm and microfractures distributed in the range of 200 nm to 5000 nm, with relative contents in the ranges of 3.44–6.79% and 0.22–1.43%, respectively. Nanoscale organic pores are the dominant type of pores, while inorganic pores and microfractures contribute much less to the shale reservoir space than organic pores. The T₂ cutoff values range from 0.55 ms to 6.73 ms, and the surface relaxivities range from 0.0032 µm/ms to 0.0391 µm/ms. Their strong correlation with TOC suggests that organic matter is the main factor controlling the pore type and structure. In addition, the main difference between NMR porosity and He porosity is that gas logging porosity is used to detect connected pores, while NMR porosity also includes closed pores and microfractures. Combined with NMR and high-temperature pressure displacement experimental facilities, this will be a further step towards studying the pore structure of shale under simulated formation conditions.

The connectivity of shale pores and the occurrence of movable oil in shales have long been the focus of research. In this study, samples from wells BX7 and BYY2 in the Eq3⁴-10 cyclothem of Qianjiang Formation in the Qianjiang depression, were analyzed. A double mercury injection method was used to distinguish between invalid and effective connected pores. The pore characteristics for occurrence of retained hydrocarbons and movable shale oil were identified by comparing pore changes in low temperature nitrogen adsorption and high pressure mercury injection experiments before and after extraction and the change in the mercury injection amounts in the pores between two separate mercury injections. The results show that less than 50% of the total connected pores in the Eq3⁴-10 cyclothem samples are effective. The development of effective connected pores affects the mobility of shale oil but varies with different lithofacies. The main factor limiting shale oil mobility in Well BX7 is the presence of pores with throat sizes less than 15 nm. In Well BYY2, residual mercury in injection testing of lamellar dolomitic mudstone facies was mainly concentrated in pores with throats of 10–200 nm, and in bulk argillaceous dolomite facies, it was mainly concentrated at 60–300 nm. The throats of hydrocarbon-retaining pores can be 5 nm or even smaller, but pores with movable shale oil in the well were found to have throat sizes greater than 40 nm. Excluding the influence of differences in wettability, the movability of shale oil is mainly affected by differences in lithofacies, the degree of pore deformation caused by diagenesis, the complexity of pore structures, and the connectivity of pore throats. Dissolution and reprecipitation of halite also inhibit the mobility of shale oil.

Due to an increasing energy demand and the depletion of conventional oil, there is ever increasing demand for unconventional shale oil and gas resources. As the most hydrocarbon-rich sag in the Junggar Basin, the development prospects for shale oil in the Mahu Sag have become a focus of research. However, so far, there have been few studies of the oil-bearing properties of shale and shale oil mobility in the sag. This paper redresses this using a range of methods, such as pyrolysis and multi-temperature step pyrolysis. The results show that the Fengcheng Formation shales are generally good quality source rocks. The main body of the shale is low mature-mature, and the type of organic matter is mostly Type II kerogen. In the depth intervals at 4616.45~4640.30 m, 4661.25~4695.20 m, 4728.30~4759.80 m, 4787.60~4812.30 m, and 4876.70~4940.25 m, the oil-bearing properties of the shale and shale oil mobility are good, with an average of more than 1.5 mg/g, OSI of more than 100 mg/g.TOC^-1, a ratio of free/adsorbed oil ( ) of more than 3, and a ratio of free/total oil ( ) of more than 80%. The second member (P₁f₂) and the lower part of the first member (P₁f₁) of the formation offer the most promising commercial prospects. Shale oil mobility in the formation is greatly affected by the abundance of organic matter. The higher the value, the greater the hydrocarbon generation capacity, and the better its adsorption capability in the shale. The Fengcheng Formation shale is mature, and shale oil mobility is good. Impacted by the main reservoir space, the felsic shale in the formation has optimal shale oil mobility, with the shale oil being characterized by self-generation and self-storage, and accumulation in adjacent layers.

The exploration of shale oil in the Fengcheng Formation of the Permian system in the Hashan area shows considerable promise, with breakthroughs in a number of shale oil exploration wells. This study evaluates the source rocks in the Fengcheng Formation in the Hashan area to determine their types, clarify the quality and hydrocarbon potentials of the different types, and analyze the main factors affecting their quality and generation potential based on lithofacies classification. The results indicate that the Fengcheng Formation in the Hashan area contains four types of lithofacies: terrigenous clastic lithofacies, dolomitic mixed lithofacies, tephra-bearing mixed lithofacies, and alkaline mineral-bearing mixed lithofacies. The tephra-bearing mixed lithofacies source rocks have the best source rock quality, followed by terrigenous clastic lithofacies and dolomitic mixed lithofacies. The quality of the source rocks is mainly controlled by their sedimentary environment (including paleoenvironment, alkaline minerals, and volcanic activity), the hydrocarbon-generating properties of the source material, and maturity. Organic matter in the dolomitic mixed lithofacies and the alkaline mineral-bearing mixed lithofacies is more concentrated in deepwater-reducing environments with medium to high salinity and arid conditions. The main biological source material is green algae (Dunaliella), which is characterized by early hydrocarbon generation and the high transformation ratio of oil, allowing for rapid hydrocarbon generation at low maturity. However, as the maturity increases, the hydrocarbon-generating potential of the source rocks decreases rapidly. Organic matter in terrigenous clastic lithofacies is more concentrated in relatively shallow water in oxygen-depleted, low-salinity, arid to semi-arid environments, with cyanobacteria being the main biological source. Cyanobacteria have the characteristics of long hydrocarbon generation periods and high hydrocarbon potential, with the peak of hydrocarbon generation occurring later than green algae (Dunaliella). Therefore, even at a relatively high maturity level, the source rocks still maintain a relatively high hydrocarbon-generating potential. Moderate volcanic activity provides favorable conditions for organic matter accumulation.

《地球科学》(ISSN 1000-2383;CN42-1874/P) (原刊名《地球科学——中国地质大学学报》ISSN 1000-2383;CN42-1233/P)，创刊于1957年，是由教育部主管、中国地质大学主办的综合性地学学术理论期刊，月刊，2015年改名为《地球科学》,她以反映中国地质大学教学与科研最新的、高水平的基础地质、应用地质、资源与环境地质及地学工程技术研究成果为主要任务。