Abstract: The Ordos Basin is rich in deep coalbed methane resources, the development of which is helpful to increase the reserve and production of oil and gas and achieve the goals of carbon peaking and carbon neutrality. Focusing on the key problem of predicting free gas content in deep coal seams, the paper proposes a new free gas content prediction model based on the validation and evaluation of the existing free gas content prediction model, when relying on pressure-retaining coring data from the eastern margin of the basin at the depth from 1 911.60 m to 1 924.84 m. The results show that the gas content of 9 pressure-retaining sealed coring samples is ranged from 4.22 m³/t to 16.35 m³/t; the free gas content is ranged from 1.24 m³/t to 2.56 m³/t, accounting for 11.00% to 36.17% of the total gas content. The difference in gas content is obviously affected by ash content, and the samples with high ash content and high density tend to have low gas content, characterized by oversaturation in the middle coal seam and undersaturation in the upper and lower coal seams. Comprehensively considering the methane gas density, water saturation and porosity of the reservoirs under certain temperature and pressure conditions, in combination with the pore space occupied by adsorbed methane, a prediction model of free gas content in deep coal seams has been constructed based on the effect of adsorption swelling. As predicted using the model, the free gas content is ranging from 1.29 m³/t to 2.69 m³/t, accounting for 10.01% to 38.54% of the total gas content, and the gas content ratio (actual gas content/theoretical maximum gas adsorption capacity) is within the range of 33.86% to 148.26%, which is highly consistent with the measured gas content in the pressure-retaining coring samples. In addition, the correlation model can be used to evaluate the gas content in deep coal seams, thus providing theoretical support for the accurate prediction and quantitative drainage and production of deep coalbed methane resources.

Key words: deep coalbed methane, free gas, gas content, pressure-retaining coring, isothermal adsorption

摘要： 鄂尔多斯盆地深部煤层气资源量丰富，实现规模开发有助于油气增储上产，助力双碳目标落实。围绕深部煤层游离气含量预测这一关键问题，以盆地东缘埋深在1 911.60~1 924.84 m煤层的保压取心数据为依托，基于已有游离气含量预测模型的验证与评价，提出了新的游离气含量预测模型。研究结果表明，9件保压密闭取心样品的含气量在4.22~16.35 m³/t，其中游离气含量为1.24~2.56 m³/t，占总含气量的11.00%~36.17%。含气量差异受灰分含量影响明显，高灰分和高密度样品的含气量偏低，在垂向上呈现中间煤层过饱和、上下煤层欠饱和的特点。综合实验和理论计算储层实际温压条件下的甲烷气体密度、含水饱和度和孔隙度等参数，结合吸附态甲烷占据的孔隙空间，构建了基于吸附膨胀效应的深部煤层游离气含量预测模型。采用该模型预测的游离气含量在1.29~2.69 m³/t，占总含气量的10.01%~38.54%，含气比（实际含气量与理论最大吸附气量的比值）在33.86%~148.26%，与保压取心样品实测含气量的吻合程度高。相关模型可应用于深部煤层的含气性评价，为深部煤层气资源的准确预测和定量排采提供理论支撑。

关键词: 深部煤层气, 游离气, 含气量, 保压取心, 等温吸附