Main controlling factors of coalbed methane well productivity and enrichment–high-yield model of the Xishanyao Formation in the Midong Block, southern Junggar Basin

【Objective】The Middle–low rank coalbed methane (CBM) resources of the Xishanyao Formation in the southern Junggar Basin are abundant. However, significant productivity differences among CBM wells in the Midong Block, coupled with an insufficient understanding of the main controlling factors and enrichment–high-yield model, restrict exploration deployment. This study aims to clarify the controlling mechanism of productivity differences in Xishanyao Formation CBM wells and establish an enrichment–high-yield model for the study area. 【Methods】Taking the No. 42–45 coal seams of the Middle Jurassic Xishanyao Formation in the Midong Block as the research object, geological parameters and production dynamic data were integrated to analyze the drainage–production characteristics and gas production stage evolution of wells with different productivity levels. Key parameters including effective coal thickness, gas content, critical desorption–storage ratio, and fracturing scale were selected. The Spearman rank correlation method was used to quantitatively identify the main controlling factors of average daily gas production and maximum daily gas production. Combined with structural zonation and typical well profile comparison, a CBM enrichment–high-yield model was constructed. 【Results】Structurally, the productivity of Xishanyao Formation CBM wells in the study area shows an overall increasing trend from the Badaowan syncline to the northern monocline. In the northern monocline, CBM well productivity is significantly controlled by geological factors: average daily gas production has the strongest correlation with effective coal thickness, while maximum daily gas production is jointly controlled by the critical desorption–storage ratio and gas content. In the Badaowan syncline, average daily gas production is significantly positively correlated with fracturing scale, indicating that engineering stimulation has a key impact on stable production capacity, whereas maximum daily gas production is obviously constrained by the critical desorption–storage ratio and gas content. The movable gas enrichment zone of the Xishanyao Formation in the study area is mainly developed in the intermediate burial depth interval (600–900 m) between the northern monocline and the northern wing of the Badaowan syncline. The spatial coupling of the critical desorption–storage ratio and effective coal thickness determines the occurrence and distribution of high-yield CBM wells. 【Conclusion】The critical desorption–storage ratio and effective coal thickness are the key parameters controlling productivity differences of Xishanyao Formation CBM wells in the Midong Block. The structural background plays a fundamental role in the formation of enrichment–high-yield zones by regulating gas redistribution and the proportion of movable gas. The intermediate burial depth interval, as a superimposed zone of hydrodynamic and structural effects, represents a favorable belt for CBM enrichment and high yield. These research results provide a theoretical basis for favorable area prediction and development deployment in the Midong Block and similar areas.