Nanopore structure characteristics and evolution of type III kerogen in marine-continental transitional shales from the Qinshui basin, northern China

Fractal Characteristics of Nanopores and Their Controlling Factors of the Lower Cambrian Shale in the Western Hubei Area, South China

“…SEM observations also revealed that OM pores in the marine shale reservoirs were well-developed, most of which displayed sponge shapes and had organic surface porosity generally >10% . However, no or only few OM pores were developed in the MCT shale, and OM surface porosity was generally <1% …”

“…However, the relationships between the fractal dimensions and various pore structure parameters are quite different in the MCT shales and their corresponding isolated kerogens. According to Lu et al, pore structure parameters of the MCT shale in the Qinshui Basin were significantly positively correlated with the D 1 values and negatively correlated with the D 2 values. However, these pore structure parameters of the corresponding isolated kerogens were weakly positively correlated with the D 1 values and not obviously correlated with the D 2 values, indicating that the OM pore was not a major factor controlling the fractal dimensions of the MCT shale.…”

“…Conventional pore structure parameters of shales mainly include pore size, pore size distribution (PSD), pore types, pore-specific surface area (SSA), and pore volume (PV). − A variety of techniques and methods has been applied to quantitatively characterize the shale pore structure, such as low-pressure CO 2 and N 2 adsorptions (LPCA and LPNA), high-pressure mercury injection (MICP), small and ultrasmall angle neutron scattering (SANS/USANS), and nuclear magnetic resonance (NMR). ,− In these methods, LPCA and LPNA experiments are usually applied to obtain PSD, SSA, and PV, which are effective in characterizing the shale pore structure. ,,− …”

Pore Peak Types and Controlling Factors of Micropores in Different Shale Reservoirs

“…As per previous studies, the highest number of occurrences is observed in the three-peak type, followed by the bimodal type. However, no uniform division standard has been established. − In this study, we divide the pore peaks into the following three categories: peak 1 (0.33–0.4 nm), peak 2 (0.45–0.65 nm), and peak 3 (0.8–0.9 nm). The positions of peaks 1 and 3 are relatively stable, and there is no secondary peak development.…”

“…Organic-rich shales in China are deposited in marine, terrestrial, and marine-land transitional environments, with significant differences in their geochemical characteristics, reservoir properties, and gas-bearing properties. − Marine shale typically has high total organic carbon (TOC) content, with a high degree of thermal evolution and organic matter dominated by types I and II; sea-land transitional shale exhibits rapid vertical changes in TOC with some cyclicity, moderate thermal evolution, and kerogen mainly type III; terrestrial shale distribution is limited, with higher TOC at the sedimentary center, lower maturity, and dominance of types I and II1 kerogen. − According to the IUPAC, pores in shales are classified as micropores (<2 nm), mesopores (2–50 nm), and macropores (≥50 nm) . Most shale gas is adsorbed in organic nanometer pores or in the surface and interlayer pores of clay minerals. − Low-temperature CO 2 adsorption experiments can quantitatively characterize the micropore characteristics in shale. − The PSD characteristics significantly affect the gas storage capacity of shale. − Research on the genesis of PSD peaks of micropores mainly focuses on coal and transitional shales. − For example, Qu et al found that the micropores in tectonic deformation coal are lamellar pores of aromatic rings or columnar pores formed by stacking .…”