Pore structure plays an essential role in the reservoir heterogeneity and methane adsorption capacity. Significant progress has been made in the pore structure classification of porous materials (such as coal and shale). Considering the pore structure characterization of the coal measures and the measuring range of high-pressure mercury intrusion porosimetry and low-pressure N2/CO2 gas adsorption, an integrated classification for coal and shale is provided. They are micropore (<2 nm), mesopore (2–100 nm), macropore A (100 nm–1 µm), macropore B (1–10 µm), and micro-fracture (>10 µm). For coal and shale samples from Guxu mining area, the micropores and mesopores largely control the gas adsorption while micro-fractures and macropore B are significant for the storage and flow of free gas. The fractal dimensions calculated from limited N2 adsorption data are not suitable for the coal samples which are not developed in mesopore and macropore A; these samples are precisely corresponding to the N2 adsorption/desorption isotherms of group B (reversible isotherm). Furthermore, the main factors influencing the methane adsorption capacity of coal and shale in the coal measures are micropore frequency, micro-fracture width, clay mineral composition, and total organic carbon content.

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Organic matter pores (OMP) provide significant storage space for hydrocarbons in lower Silurian Longmaxi shales in the Dingshan field of southern Sichuan, China. The distributions of organic matter and the different OMP structure parameters were characterized through Ar-ion polishing, scanning electron microscopy (SEM), and image analysis software for shale samples of different wells. The research results indicated that organic matter has been divided into two categories based on its occurrence, location, and its relationship with authigenic minerals: organic matter in situ and migrated organic matter. OMP for organic matter in situ are mainly micropores mostly arranged isolatedly, while in migrated organic matter pores show larger sizes and higher roundness. The development of OMP in samples is predominantly controlled by the formation pressure. The existence of overpressure alleviated the stress on the rock skeleton, causing the compaction of some migrated organic matters to lag or decrease. This played a positive role in protecting the development of pores in the interior and edge of the rock skeleton, and it can also induce the development of microfractures in shale. The protective effect of formation pressure on organic pores was provided for understanding the exploration and exploitation of Longmaxi shales in the study area.

In recent years, the typical crude oil from the Cambrian Lower Ordovician source rocks has been found in the Tarim Basin, and it is characterized by 13C enrichment. The stable carbon isotope of the oil is concentrated at approximately −28‰, which is 3‰–6‰ heavier than that of the crude oil from the Middle and Upper Ordovician source rocks. The stable carbon isotope between crude oil and its kerogen is characterized by inversion, with an amplitude of approximately 3‰–4‰. However, the origin of this phenomenon remains controversial, which restricts the next exploration of crude oil in the Cambrian–Lower Ordovician in the Tarim Basin. Samples were collected from seven outcrop profiles in the Kuruketage region. The basic geochemical features of the Cambrian strata, including total organic carbon abundance, δ13Corg, δ13Ccarb, and δ18Ocarb, were studied and compared with those of well TD2. The results show that the lithologies, isotope stratigraphic evolutional curves, and correlations between the organic carbon and inorganic carbon of the profiles from the northern Kuruketage region are successively comparable with those of the profiles from the southern Kuruketage region and the well TD2. In this study, the carbon isotope records are supposed to indicate a vertical gradient Cambrian oceanic mode, including the shallow decoupled isotope zone, middle gradient‐coupled isotope zone, and deep isotope‐decoupled zone. The discovery of this isotope record reflects the formation of stable carbon and oxygen isotope stratified oceans during the Cambrian period. Additionally, it provides important insights into the origin of the 13C enrichment observed in some Lower Cambrian crude oils in the Tarim Basin.