Characteristics of High Steep and Low Rank Coal Seam and its Influence on Gas Bearing in Southern Margin of Junggar

The southern margin of the Junggar Basin is rich in coalbed methane CBM) resources, characterized by a steep coal seam dip angle, complex tectonic stress, low-rank coal and rock, uneven spatial distribution of gas content, and significant variations in carbon dioxide content. To guide the efficient development of CBM in steeply dipping, low-rank coal seams, it is critical to investigate coal seam development features and clarify the factors influencing gas content. This study focuses on Block M in the southern Junggar Basin, targeting the coal and rock of the Jurassic Xishanyao Formation. Through field geological surveys, on-site core observations, laboratory experiments, and integrated analysis of drilling, logging, and field test data, we analyzed the characteristics of steeply dipping, low-rank coal seams in the region, as well as the spatial distribution patterns of gas and carbon dioxide content. Furthermore, we examined key controls on CBM storage, including coal seam properties and hydrogeological conditions, to elucidate the effects of coal lithology, coal quality, burial depth, coal structure, and hydrogeology on the spatial variability of gas content. The results indicate that low coal rank and high mineralization of formation water are the primary factors contributing to elevated carbon dioxide content. These findings provide valuable insights into the enrichment mechanisms of CBM in steeply dipping, low-rank coal seams and support the evaluation of favorable “sweet spot” areas for exploration.