No abstract

No abstract

The pore structure and fractal characteristics of the Lower Cambrian marine organic-rich shale in southern China were comprehensively studied using low-pressure [Formula: see text] adsorption and organic geochemical experiments, X-ray diffraction, petrophysical property tests, and scanning electron microscope observations. The results indicate that the total organic carbon (TOC) content of the study shale varies between 0.45% and 8.50%, with an average value of 3.97%. The adsorption isotherm of the shale samples belongs to type IV, and slit-type pores are the predominant pore type in these shales. The shale has a Brunner–Emmet–Teller specific surface area ranging from 1.83 to [Formula: see text], a pore volume ranging from 0.00398 to [Formula: see text], and an average pore diameter ranging from 3.61 to 15.19 nm. Organic matter pores (OMPs) are the main contributors to the specific surface area and the pore volume. The organic matter is closely symbiotic with the epigenetic quartz. We have obtained two fractal dimensions ([Formula: see text] and [Formula: see text]) of the shale using the Frenkel-Halsey-Hill method. It was found that [Formula: see text] is suitable for the quantitative characterizing of the pore structure of nanopores inside the shale due to its good correlation with the TOC content and pore structure parameters. When the TOC content of the shale exceeds 4%, the main pore type inside the shale is OMP and the [Formula: see text] value mainly reflects the fractal characteristics of OMP. Moreover, we analyzed the seepage characteristics of different types of pores. It was found that the parallel plate-like pores and the slit-type pores are more favorable for fluid seepage than the ink bottle-like pores. The shale with [Formula: see text] and [Formula: see text] type pore structures should be the key exploration targets for the target shale in the study area.

One of the challenges in evaluating and estimating the gas storage and migration of coal has been the investigation of complex pore structures, especially in the nanoscale. The present study provides new insights into nanoscale pore types, and the genesis, classification, and structure characteristics of high-rank coal by investigating 10 anthracite coals in the Shanxi Formation and Taiyuan Formation of the Xinjing Coal Mine in the Qinshui Basin, North China. A series of experiments that combined the qualitative observation method of argon ion polishing technology in combination with field emission-scanning electron microscope and quantitative analysis methods of low-pressure N 2 gas adsorption and mercury intrusion porosimetry were performed to characterize nanoscale pore structures and its influence on gas behavior. The results revealed that various types of nanoscale pores exist in the coal matrix. Descriptive classifications for nanoscale pores consist of three major groups (organic matter pores, mineral-related pores, and micro-fractures), and nine subtypes was summarized to correlate pores to the networks. Furthermore, mercury intrusion porosimetry, low-pressure N 2 gas adsorption, and image processing were combined to determine the pore size distributions, indicating that pore sizes are bimodally distributed with two broad peaks. The major peak at approximately 20-400 nm was mostly associated with isolated microscopic organic constituents interparticle nanopores, while a minor but prominent peak at the macro-pore to micro-fracture scale was more associated with epigenetic pores, mineral-related pores, and micro-fractures. Furthermore, image processing also provides a specialized approach to reveal the structure and diameter of different types of nanoscale pores. The combination of quantitative test and

Transitional upper carboniferous Shanxi Formation coal-bearing strata in Qinshui Basin have been proven to be a set of mixed unconventional gas-bearing reservoirs forming a multi-superimposed gas system that consists of multiple independent fluid pressure systems vertically through the strata. An experimental protocol was designed to compare the pore networks in high-rank coal, shale, and tight sandstone reservoirs from Shanxi Formation using quantitative and qualitative experimental methods, including high-pressure mercury injection porosimetry (MIP), low-pressure nitrogen gas adsorption (LN2GA), and argon ion polishing–field emission scanning electron microscope (AIP-FESEM). The results show that genetic and structural differences in pore types, morphology, abundance, and proportion in coal, shale, and tight sandstone reservoirs are significant, reflecting strong heterogeneity characteristics. Pore networks determine the roles of different types of reservoirs in gas-bearing systems through differentiated pore structure, development degree, and spatial distribution. Due to the differences in nanopore development and connectivity, coal and tight sandstone reservoirs provide important reservoir spaces for adsorbed and free gas in the system. Thus, they become influential factors controlling the relationship between the gas-bearing subsystems with different fluid pressures. The lack of mesopores in shale and relatively weaker heterogeneity between layers lead to the phenomenon that continuously developed shales of a specific thickness are more likely to be the interlayers that divide the superimposed gas-bearing system. Systematic comparison of pore development characteristics will provide scientific support to further explain the formation mechanism of multi-superimposed gas systems in coal-bearing strata from the perspective of pore networks and provide guidance for the development of unconventional natural gas in coal-bearing strata.