Study on gas enrichment mechanism in goaf of coal mine in Pingle Depression, Jiangxi Province
江西省萍乐坳陷煤矿采空区瓦斯富集机理研究

摘要

为有效防治瓦斯灾害并推动煤层气资源开发，本研究旨在系统揭示江西省萍乐坳陷丰城煤矿区主采B₄煤层中瓦斯富集的关键地质控制机理，核心科学问题是厘清控制该矿区瓦斯非均质赋存的主导地质因素及其耦合关系。本研究采用多手段综合分析方法，系统整合了区域地质勘探、钻孔数据、煤质测试（包括镜质组反射率测定与工业分析）及瓦斯参数实测数据，重点从顶底板岩性、煤层埋深、煤层厚度、煤变质程度及地质构造等核心地质控气因素出发，对瓦斯赋存规律进行定量与定性相结合的综合研究。研究表明，B₄煤层瓦斯赋存受多因素协同控制：①岩性控制：致密顶底板（如泥岩、粉砂岩）是优良封闭层，而上覆S5砂岩“西厚东薄”的分布直接导致瓦斯含量“东低西高”。②埋深效应：瓦斯含量总体随埋深增加而增大，但在局部构造复杂区（如第2～5勘探线）出现异常。③煤厚影响：瓦斯含量与煤层厚度呈正相关，煤层“南薄北厚、西薄东厚”的分布与瓦斯“南小北大、西高东低”的格局高度吻合。④煤级作用：B₄煤层处于焦煤-瘦煤的中变质阶段（Ro=1.4%～1.895%），其生气潜力与强吸附能力共同促进瓦斯富集。⑤构造控气：曲江向斜北翼与轴部等挤压构造区是瓦斯富集区，而开放性断层及南翼古风化剥蚀带则导致瓦斯逸散。丰城矿区B₄煤层的瓦斯富集是“生、储、盖、保”动态系统共同作用的结果，其“东低西高、南低北高”的分布格局受中变质煤的生气潜力、顶底板封闭能力、煤层储集条件及构造保存/逸散效应的综合控制。本研究成果为矿区瓦斯赋存规律精准预测及差异化治理策略的制定提供了关键地质理论依据。

Abstract

To effectively prevent gas disasters and promote the development of coalbed methane resources, this study aims to systematically reveal the key geological control mechanisms of gas enrichment in the main B₄ coal seam of the Fengcheng mining area, Pingxiang-Le'an Depression, Jiangxi Province. The core scientific problem is to clarify the dominant geological factors controlling the heterogeneous gas occurrence in this mining area and their coupling relationships. This study adopted a multi-method integrated analysis approach, systematically combining regional geological exploration, borehole data, coal quality testing (including vitrinite reflectance determination and industrial analysis), and measured gas parameter data. The research focused on key geological gas-control factors such as roof and floor lithology, coal seam burial depth, coal seam thickness, coal metamorphism degree, and geological structures, conducting a comprehensive study that combined quantitative and qualitative analysis of gas occurrence patterns. The research indicates that gas occurrence in the B₄ coal seam is controlled by the synergistic effect of multiple factors: ① Lithological Control: Dense roof and floor strata (e.g., mudstone, siltstone) act as excellent seals, while the "thicker in the west, thinner in the east" distribution of the overlying S5 sandstone directly leads to a gas content pattern of "lower in the east, higher in the west." ② Burial Depth Effect: Gas content generally increases with burial depth, but anomalies occur in locally structurally complex areas (e.g., between exploration lines 2–5). ③ Coal Thickness Influence: Gas content is positively correlated with coal seam thickness. The coal seam distribution pattern of "thinner in the south, thicker in the north, thinner in the west, thicker in the east" highly aligns with the gas pattern of "lower in the south, higher in the north, lower in the east, higher in the west." ④ Coal Rank Effect: The B₄ coal seam is in a medium metamorphic stage (coking coal to lean coal, Ro=1.4%–1.895%). Its gas generation potential and strong adsorption capacity jointly promote gas enrichment. ⑤ Structural Control: Compressional structural areas such as the northern wing and axis of the Qujiang Syncline are gas enrichment zones, while open faults and the ancient weathering denudation zone in the southern wing facilitate gas escape. The gas enrichment in the B₄ coal seam of the Fengcheng mining area results from the combined effects of a dynamic "generation, storage, seal, and preservation" system. Its distribution pattern of "lower in the east and higher in the west, lower in the south and higher in the north" is comprehensively controlled by the gas generation potential of medium-metamorphic coal, the sealing capacity of the roof and floor, coal seam reservoir conditions, and structural preservation/escape effects. The findings of this study provide a key geological theoretical basis for the accurate prediction of gas occurrence patterns and the formulation of differentiated management strategies in the mining area.