Gas‐Bearing Characteristics and Controlling Factors of Low‐Rank Coalbed Methane in the Shengli Coalfield, Jiergalangtu Sag, Erlian Basin

The Lower Cretaceous Saihantala Formation in the Shengli Coalbed Methane (CBM) field of the Jiergalangtu Sag, Erlian Basin, contains exceptionally thick, low‐rank coal seams. These seams exhibit significant heterogeneity in gas content and physical properties, with high water saturation that constrains economically viable development. To investigate the gas‐bearing characteristics and the dominant controlling factors, this study integrates systematic coring data, including centimetre‐scale descriptions, gas content measurements, maceral analysis and nuclear magnetic resonance (NMR) logging. The results reveal that the area is primarily composed of two coal lithotypes: woody coal, characterized by high huminite content (> 85%) and abundant nanoscale micropores, forms a high‐adsorption, low‐permeability system favourable for gas preservation. In contrast, clastic coal, with higher inertinite content and well‐developed macropores, has a permeability approximately 10 times greater than that of woody coal, facilitating gas escape. The gas content of the primary IV coal group exhibits a vertical ‘sandwich’ pattern (high‐low‐high) and a planar decreasing trend from the central depression towards the margins, both of which are controlled by the coal lithotype assemblages and the depositional environments. The dominant factor controlling gas content is the coal lithotype and its associated pore structure. High‐gas‐content zones correspond to areas with woody coal content greater than 52%. This study elucidates the mechanisms underlying high gas content in low‐rank coals with high huminite content and effective preservation conditions, providing key insights for identifying sweet spots and optimizing the development of similar CBM fields.