Search

The current studies primarily analyze the heterogeneity and complexity of mesopore structures based on low-temperature nitrogen (N2) adsorption curves and the Frenkel–Halsey–Hill (FHH) fractal model. However, these studies ignore the fact that the low-temperature N2 desorption curve can also reflect the desorption performance of the mesopore structure. In this research, novel fractal indicators for characterizing the adsorption–desorption performance of mesopores based on the fractal dimension from the N2 adsorption curves and N2 desorption curves are proposed. The novel fractal indicators I1 and I2 are applied to evaluate the adsorption–desorption performance of mesopores with pore size 2–5 nm and pore size 5–50 nm, respectively. The fractal indicator I1 shows an increasing trend with coalification, reflecting that the gas adsorption performance of 2–5 nm mesopores is enhanced with coalification. The fractal indicator I2 exhibits a trend of first increasing and then decreasing with coalification, indicating the gas desorption performance of mesopores with pore size 5–50 nm decreases first and then increases. The proposed indicators provide novel analytical parameters for further understanding the gas adsorption–desorption mechanism of porous coal-based or carbon-based materials. [ABSTRACT FROM AUTHOR]

To gain insights into the spectroscopy characteristics from coal to graphite, we investigated different metamorphic degrees of coal-based graphite which were collected from Hunan Province China. In this paper, by means of Xray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, graphite with different metamorphism degrees has been characterized to explore the evolution of macromolecular structure of organic matter during graphitization. The results show that with the increase of metamorphism degree, the 002-diffraction peak of the series of samples gradually shrinks and narrows, and the peak intensity becomes stronger, indicating that the microcrystalline structure gradually becomes regular and ordered. As the degree of graphitization increase, the uniformity of particle size in coal samples observed gradually increases, and the morphology becomes more regular, transitioning from disordered and irregular shapes to a structured large-scale flake pattern. The crystallinity improves, and the massive coal particles gradually coalesce into large plate crystals, with the inter-particle pores gradually closing. The graphite structure becomes increasingly evident. The FTIR spectra show that as the degree of graphitization increases, the peak at 1,581 cm-1 corresponding to C=C vibrations gradually intensifies. Some inert functional groups are retained throughout the graphitization process. The pores between coal particles gradually close, and the morphology of graphite particles becomes more regular and ordered. Additionally, during the graphitization process, structures similar to carbon nanotubes may develop. Throughout the structural transformation from coal macromolecules to graphite crystals, the size of the sp2 planar domains in single-layer graphene increases, and the lattice structure of carbon atoms gradually enlarges. These findings contribute to a comprehensive understanding of the properties and characteristics of coal-derived graphite, and can provide theoretical reference and basis for the metallogenic mechanism of coal-derived graphite and the efficient utilization of coal. [ABSTRACT FROM AUTHOR]

Faults, as a kind of fracture tectonics, play a role in reservoir closure or provide oil and gas transportation channels. The accurate understanding of the distribution characteristics of faults is significant for oil and gas exploration. The traditional fractal dimension for fault number (Df3) cannot comprehensively characterize the complexity and heterogeneity of fault network distribution. In this paper, a fractal characterization method on three-dimensional (3D) tortuosity of fault tectonics is proposed based on 3D seismic exploration. The methodology is described in detail to establish the model on the fractal dimension for the 3D tortuosity of fault tectonics. The results show the proposed method of estimation of the DT3 displaying high accuracy and rationality. Compared with the traditional fractal dimension Df3, the proposed DT3 can comprehensively characterize the fractal characteristics of faults network systems in the 3D space. This study achieves a breakthrough in the fractal characterization of the 3D tortuosity of fault tectonics. It is worth further study for establishing an analytical fractal equation based on the DT3 and oil or gas transfer, which can provide the theoretical foundation and technical support for oil and gas exploration. [ABSTRACT FROM AUTHOR]

Affected by geology and mining, a certain number of low-yield wells will appear after a period of production in coalbed methane wells, and technical repairs are urgently needed to restore their production capacity to the maximum. Therefore, it is of great significance to establish a reasonable and feasible theoretical standard to evaluate the workover priority of CBM wells for the efficient utilization of CBM resources. From the perspectives of technical feasibility and economic rationality, eight key indicators that affect the cost performance of CBM well workover are screened. Combining the entropy value method and the TOPSIS comprehensive ranking method, the surface coalbed methane well repair priority entropy value-TOPSIS comprehensive evaluation model was constructed, and the surface coalbed methane well repair priority evaluation was carried out by taking 9 surface coalbed methane wells that urgently needed to be repaired in a mine as the evaluation objects. The evaluation results show that among the economic indicators, the average gas production per meter in the 30 days before the coal bed methane well was stopped and the cumulative gas production per meter before the stop had a relatively high weight, which were 29.68% and 13.83% respectively, This shows that in coalbed methane well workover operations, the long-term gas production potential of the coalbed methane well and the gas production capacity when disturbed by harmful factors are the decisive factors affecting the priority of coalbed methane well workover; Among the technical indicators, the degree of casing deformation and the depth of the coalbed methane well have a relatively high weight, accounting for 11.34% and 9.90% respectively, This shows that the smaller the deformation of the wellbore casing and the shallower the depth of the coalbed methane well, the higher the priority of the workover of the coalbed methane well; The ranking of the production recovery rates of the three coalbed methane wells in the Pingdingshan mining area after workover operations is consistent with the results output by the evaluation model, which proves that the evaluation model is reasonable for determining the priority of workovers for damaged wellbores; This evaluation model can provide a theoretical reference for small and medium-sized coalbed methane development companies to determine the priority of workovers. [ABSTRACT FROM AUTHOR]