Research on recoverable reserves and gas production characteristics of coalbed methane wells in Baode block of Ordos Basin

In order to clarify the gas production characteristics of medium and low rank coalbed methane wells in different regions of the Baode block of the Ordos Basin, and to guide strategy development, methods such as the Arps decline analysis, production accumulation method, and flowing material balance method were applied in conjunction with actual production data from the block to establish a calculation method for recoverable coalbed methane reserves applicable to different stages of development. Through the comprehensive application of data statistics, production dynamic analysis, and other methods, the recoverable reserves and gas production characteristics of three development units (Development Unit 1 to Unit 3) in the block were systematically studied. By comparing geological and development parameters, the influence of geological condition differences on gas production characteristics was clarified. The results showed that from north to south (Development Unit 1 to Unit 3) in the Baode block, the daily gas production during the stable production period decreased from 3 314 m³ to 864 m³, the gas recovery rate declined from 3.82% to 0.99%, the recoverable reserves reduced from 1 391×10⁴ m³ to 399×10⁴ m³, and the recovery factor dropped from 48.50% to 16.99%. Meanwhile, the gas breakthrough time extended from 99 days to 228 days, and the stable production duration increased from 981 days to 1 553 days. Correlation analysis showed that daily gas production during the stable production period was significantly correlated with the temporary storage ratio, critical desorption pressure, and the thickness of the 8+9 coal seam, while recoverable reserves were highly correlated with the thickness of the 8+9 coal seam and the gas content of the 4+5 coal seam. A comparison of geological parameters indicated that the main coal seam thickness, gas content, and temporary storage ratio in Development Unit 1 were superior to those in Development Unit 2 and Unit 3, and the preservation conditions were also better. The study concludes that the north-south differences in gas production characteristics of the Baode block are primarily influenced by geological conditions. The northern Development Unit 1 has superior resource conditions, with thicker coal seams, higher gas content, and a larger temporary storage ratio, resulting in higher stable gas production and higher recovery rates. The southern Development Unit 3 has poorer resource conditions, leading to lower stable gas production but longer stable production periods. The findings provide a scientific basis for the efficient development of medium and low rank coalbed methane fields and the optimization of different unit drainage systems in the Baode block.