Abstract: Deep coalbed methane (CBM) resources are abundant in Daning-Jixian block in the eastern margin of Ordos Basin, and the development practice in recent years has broken through the traditional understanding that it is difficult to develop and utilize deep CBM resources. At present, there are still a series of geological problems unsolved in the exploration and development of deep CBM, and especially the control factors of gas-bearing properties and the prediction of free gas content seriously restrict the resource evaluation and efficient development of deep CBM. Comprehensively using the geological data of CBM development and experimental testing methods, the paper compares and analyzes the differences in gas content between mid-deep coal seams (with buried depth from 1 000 m to 1 500 m) and deep coal seams (with buried depth greater than 1 500 m) in Daning-Jixian block, thus discovering the internal and external controlling factors of gas content in deep coal seams, and establishing the prediction models and vertical distribution patterns of gas content in different phases. The results show that the gas oversaturated coal reservoirs are generally detected in deep layer, of which the free gas proportion is from 17% to 43% and tends to increase with reservoir pressure. The free gas content is negatively correlated with water saturation. Before adsorption and saturation, coal reservoir pressure can promote the adsorption of methane by coal seams, while temperature and moisture can inhibit the adsorption of methane. Compared with low-rank coal, high-rank coal has stronger methane adsorption capacity, which is mainly attributed to the material composition of coal, pore structure, physical and chemical reactions between methane molecules and coal surface. Due to many limitations, the adsorbed gas content in coal seams presents a changing trend from "rapid rise to slow growth to slow decline" with the increase of buried depth, while the free gas content presents a trend from "stable rise to slow growth to being constant". Therefore, the change of total gas content in coal reservoirs with buried depth is divided into four evolution stages:rapid rise, slow rise, remaining stable and slow decline.

Key words: deep coalbed methane, free gas, gas content, controlling factors, prediction model, distribution pattern

摘要： 鄂尔多斯盆地东缘大宁—吉县区块深部煤层气资源丰富，近年来的开发实践打破了深部煤层气资源难以开发利用的传统认识。目前，深部煤层气勘探开发仍存在一系列地质难题尚未解决，特别是煤层的含气性控制因素及游离气含量预测等，严重制约着深部煤层气的资源评价与高效开发。综合利用煤层气开发地质资料和实验测试手段，对比分析大宁—吉县区块中—深部煤层（1 000~1 500 m）与深部煤层（大于1 500 m）的含气性差异，揭示了深部煤层含气性的内在与外在控制因素，建立了不同相态煤层气的含气量预测模型与垂向分布模式。研究结果表明：深部煤储层整体处于含气过饱和状态，其游离气占比为17%~43%，且随着储层压力升高呈增大的趋势，游离气含量与含水饱和度呈负相关关系。在达到吸附饱和之前，煤储层压力对煤层吸附甲烷有促进作用，而温度和水分则会抑制甲烷的吸附作用。相对于低阶煤而言，高阶煤对甲烷的吸附能力更强，这主要与煤岩的物质组成、孔隙结构、甲烷分子与煤表面之间发生的物理化学反应等因素相关。受多种因素共同制约，煤层中的吸附气含量随着埋深的增大呈现出"快速升高—增速减缓—缓慢下降"的变化趋势，游离气含量呈现出"稳定升高—增速减缓—趋于恒定"的变化趋势。由此，可将煤储层总含气量随埋深的变化整体划分为快速升高、缓慢升高、保持稳定、缓慢下降4个演化阶段。

关键词: 深部煤层气, 游离气, 含气量, 控制因素, 预测模型, 分布模式