International Journal of Coal Geology最新文献

Although artificial maturation of hydrocarbon source rocks by laboratory pyrolysis is far from representing natural maturation, it is a useful tool to investigate the process. In this study, we used routine open system pyrolysis for powder samples and Restricted System anhydrous Pyrolysis (RSP) for cm-sized Silurian shale source rock fragments to artificially mature the samples to different end-temperatures in the presence of a flowing carrier gas. Maturation experiments on rock fragments enable the simulation of physical barriers for the generated hydrocarbons that need to be overcome before expulsion from the source rock can occur. Based on the artificial maturation results in this study, oil expulsion efficiency from the Silurian shale source rock was 46% at the early oil generation stage and increased to 74% at approximately the peak oil generation stage.

Furthermore, we have compared artificial maturation results from powder-form and fragment-form samples with natural-maturation series and found that artificial maturation of fragment-form samples sufficiently resembles natural maturation of the Silurian shales. It is therefore possible to simulate the early, middle and peak oil generation stages of natural maturation and expulsion efficiencies. This implies that, lab-based oil expulsion efficiencies from increasing maturity and hydrocarbon generation can be incorporated into the basin modeling.

Unconventional hybrid petroleum systems are partially to entirely self-sourced. Their hydrocarbons are generated within internal (intraformational) organic-rich mudstone source rocks and subsequently migrate into adjacent organic-lean reservoir beds composed of sandstone, siltstone or carbonate. Hybrid systems with volumetrically dominant reservoir-quality rocks can additionally receive hydrocarbon charge by longer-range migration from external source rocks. However, few previous studies of hybrid systems have focused on the migration and mixing of hydrocarbons from both internal and external sources. To address this shortfall, this study presents an integrated organic geochemistry and stable carbon isotope investigation of drill-core and produced hydrocarbon liquid samples from two wells in a major unconventional hybrid petroleum system in the Montney Formation of western Canada. The results reveal distinct geochemical trends with increasing depth through the upper part of the Montney Formation including decreased C₃₀₊ biomarker compounds, increased depletion of saturate compared to aromatic δ¹³C values, and increased proportions of saturates and mobile oil. These trends indicate that oil from external source rocks of the overlying Doig Formation migrated into the upper part of the Montney Formation. Downward migration of externally sourced Doig oil resulted in a broad transition zone where Doig-sourced oil mixed with locally migrated lighter oil generated within internal Montney source rocks of slightly higher thermal maturity. This study sheds new light on the migration and mixing of disparate oil charges in the Montney Formation, and likely has widespread applicability to other similar unconventional hybrid petroleum systems that had hydrocarbon contributions from both internal and external source rocks.

Accurate quantification of the coexistence of adsorbed and free gas content holds the utmost significance for estimating gas-in-place resources and predicting gas production dynamics. In this study, we conducted real-time isothermal adsorption experiments and NMR fluid monitoring on stress-confining core samples, from the Zhengzhuang Block's No.3 coal seam in the southern Qinshui Basin. Our focus was on assessing multi-phase methane gas contents within coal under various pressure and temperature (P/T) conditions. By integrating experimental findings with adsorption potential theory and the SDR adsorption model, we developed comprehensive models for adsorbed, free, and total gas contents as functions of P/T and water/gas volume saturation. Utilizing these models, we predicted vertical variations in adsorbed and free gas contents within the coal seam. Our results revealed that the interplay between positive reservoir pressure effects and adverse reservoir temperature effects influenced both adsorbed and free methane gases. With increasing burial depth, the influence of pressure on adsorbed gas diminished, while temperature effects became more pronounced. Conversely, free gas content responded noticeably to reservoir pressure, with temperature exerting a marginal influence. Additionally, we performed a numerical simulation to reconstruct the thermal history, burial trajectory, and evolution of reservoir pressure for the No.3 coal seam. The simulation results served as foundational data for understanding the evolution of free and adsorbed gas contents across different geological epochs within the in-situ reservoir. Our findings unveiled a four-stage evolutionary progression in both adsorbed and free gas contents, correlating with the uplift and subsidence of the coal seam. In conclusion, our study provides a conceptual model elucidating the intricate, deep-time evolution process and mechanisms governing the occurrence of multiphase gases across distinct geological epochs. The implications of this research are crucial for accurately evaluating gas-in-place resources and guiding the exploration and development of deep coalbed methane resources.

Natural graphite is a critical raw material and its substitution in some applications will contribute to reduce its supply risk. Coal ash, which is still produced in high amounts, contains a carbonaceous solid residue (char) that may be a substitute of natural graphite. For this purpose, char may be graphitized and used in electrocatalysis reactions, however char properties depend on coal rank, composition and combustion conditions that affect the graphitization process. Research on industrial coal char graphitization is limited, resulting in restricted comprehension of the contributing factors. In order to provide novel insights, industrial residual chars (derived from Poland, Portugal, Romania and South Africa) subjected to high-temperature treatments (carbonization at 1000 °C followed by treatment at 2600 °C under environmental pressure) were examined regarding their microstructural and microtextural transformations. The samples were studied by focussing on its heterogeneity, namely its specific properties and interactions, including elemental composition, optical character, and structure. Furthermore, the evolution of structural order of selected char morphotypes in samples derived from coal of similar rank was assessed using Raman microspectroscopy.

The results highlighted a set of aspects that could have influenced the transformations experienced by the different chars during high temperature treatments (graphitization). It was found that Hydrogen might play a role in the graphitization ability of isotropic chars derived from low rank coal. The prior preferential orientation of the Basic Structural Units (BSU) contributes to achieve a higher graphitization degree, but it can be enhanced or hindered by other factors, e.g., hydrogen content. Raman microspectroscopy showed that char morphotypes from the same group underwent different transformations during graphitization, indicating that morphotypes or sections with unfused optical character may be more prone to graphitization. However, the existence of disordered domains and specific microtextures, such as polyhedral pores identified under TEM, likely hindered further graphitization. Further research on this topic is needed.

Permeability plays a significant role in the economic viability of coalbed methane (CBM) development. In China, in situ permeability obtained from injection fall-off tests range from 0.0001 to 41 mD at depths of 130–1728 m, with the majority (78%) falling between 0.01 and 1 mD. Coal reservoirs with high rank, common cleat mineralization, and depth-dependent high stress may result in extremely low permeability. Low-rank coal and cataclastic coal exhibit more favorable permeability conditions at shallow depths. Heterogeneity in coal rank, coal texture, and stress magnitude results in a discrete distribution of permeability both regionally and vertically. Most deep seams are highly compressed with extremely low permeability (<0.1 mD) as high stress levels. Multilateral horizontal wells work best with high permeability seams, while vertical wells with conventional hydraulic fracturing demonstrate limited adaptability to deep and low-permeability seams due to insufficient proppant-supported fractures. With increasing depth, both vertical and horizontal wells should employ larger fracturing scales to create effectively supported zones with higher fracture conductivity and reduced stress sensitivity to enhance CBM productivity. Horizontal wells with large-scale volume fracturing demonstrate superior performance compared to vertical wells in extracting CBM from deep, low-permeability, and high gas saturation reservoirs.

Coal and gas outbursts are a major cause of fatalities in underground coal mines and pose a threat to coal power generation worldwide. Among the current mitigation efforts include monitoring methane gas levels using sensors, employing geophysical surveys to identify geological structures and zones prone to outbursts, and using empirical modeling for outburst predictions. However, in the wake of industry 4.0 technologies, several studies have been conducted on applying artificial intelligence methods to predict outbursts. The proposed models and their results vary significantly in the literature. This study reviews the application of machine learning (ML) to predict coal and gas outbursts in underground mines using a mixed-method approach. Most of the available literature, with a focus on ML applications in coal and gas outburst prediction, was investigated in China. Findings indicate that researchers proposed diverse ML models mostly combined with different optimization algorithms, including particle swarm optimization (PSO), genetic algorithm (GA), rough set (RS), and fruit fly optimization algorithm (IFOA) for outburst prediction. The number and type of input parameters used for prediction differed significantly, with initial gas velocity being the most dominant parameter for gas outbursts, and coal seam depth as the dominant parameter for coal outbursts. The datasets for training and testing the proposed ML models in the literature varied significantly but were mostly insufficient - which questions the reliability of some of the applied ML models. Future research should investigate the effect of data size and input parameters on coal and gas outburst prediction.