Coal bed methane (CBM) has recently been produced from sub-bituminous to high volatile bituminous low rank coals (vitrinite reflectance 0.39 to 0.53%) from the Paleocene Cuervos Formation in the Cesar Sub-basin, Colombia. Understanding CBM gas origin is vital for designing exploration and production strategies, in order to target either shallow economic accumulations of microbial gas or deeper and thermally mature coal seams. In this context, this study aims to determine whether thermogenic gas, biogenic gas, or a mixture of both gas types have contributed to gas yield in the Cesar Sub-basin; it also discusses the relationship between gas origin and tectonics. For the first time, co-produced waters and gas samples from CBM multi-seam production wells and shallow aquifer water-wells were collected in the Boqueron compartment (Cesar Sub-basin) and were analysed via stable isotope composition and molecular geochemistry. Structural compartmentalisation in the Sub-basin as a result of interplate shortening during the Mid-Paleogene has resulted in slightly different coal ranks, saturation, and gas contents between compartments of the Paleocene Cuervos Formation. This event could have interrupted early thermogenesis and allowed the introduction of meteoric waters carrying bacteria consortia responsible for biogenesis.

The produced waters from the CBM wells were HCO₃ > Na⁺ > Cl⁻ type, and ranged in TDS (Total dissolved solids) from 2268 to 6602 mg/L (avg. 3887 mg/L). Recently revised genetic diagrams of δ¹³C-CH₄ versus δ²H-CH₄ and additional parameters, such as gas dryness ratio and water chemistry, corroborated biogenesis as the main gas origin. Carbon isotopic differences between carbon dioxide and methane (Δ¹³C_H2O–CH4), as well as those of hydrogen isotopes in water and methane (Δ²H_H2O–CH4), also indicated a typical microbial CO₂ reduction pathway. The positive carbon isotope composition of dissolved inorganic carbon (δ¹³C-DIC) not only showed a clear differentiation between waters from CBM wells and those from shallow aquifers, but also confirmed the occurrence of methanogenesis when paired with high alkalinity. In addition, the water quality analysis showed increasing sodium and bicarbonate concentrations with depth, which is typical of CBM production basins. Although biogenic gas was identified, tectonic settings do not seem to explain gas origin occurrence, since secondary biogenesis was expected in an uplifted basin such as Cesar Rancheria. Isotopic data was not decisive in differentiating primary versus secondary biogenesis, since the gas isotope compositions plot close to the boundary between the primary and secondary biogenic gas fields. Further studies on isotopic chemistry are required to refine this interpretation and confirm gas generation in the other two compartments.

煤层气 (CBM) 最近由来自哥伦比亚 Cesar 次盆地的古新世 Cuervos 地层的亚烟煤到高挥发性烟煤低阶煤（镜质体反射率 0.39 至 0.53%）生产。了解煤层气成因对于设计勘探和生产策略至关重要，以便针对微生物气体的浅层经济积累或更深的热成熟煤层。在此背景下，本研究旨在确定热成因气、生物成因气或两种气体类型的混合物是否对 Cesar 次盆地的天然气产量做出了贡献；它还讨论了天然气成因与构造之间的关系。首次，来自 CBM 多煤层生产井和浅层含水层水井的联产水和气体样品被收集在 Boqueron 隔间（Cesar 次盆地）中，并通过稳定同位素组成和分子地球化学进行分析。由于中古近纪期间的板间缩短，子盆地中的结构分区导致古新世 Cuervos 组各分区之间的煤等级、饱和度和气体含量略有不同。这一事件可能会中断早期的产热，并允许引入携带负责生物发生的细菌聚生体的大气水域。由于中古近纪期间的板间缩短，子盆地中的结构分区导致古新世 Cuervos 组各分区之间的煤等级、饱和度和气体含量略有不同。这一事件可能会中断早期的产热，并允许引入携带负责生物发生的细菌聚生体的大气水域。由于中古近纪期间的板间缩短，子盆地中的结构分区导致古新世 Cuervos 组各分区之间的煤等级、饱和度和气体含量略有不同。这一事件可能会中断早期的产热，并允许引入携带负责生物发生的细菌聚生体的大气水域。

煤层气井的采出水为 HCO ₃  > Na ⁺  > Cl ^-类型，TDS（总溶解固体）范围为 2268 至 6602 mg/L（平均 3887 mg/L）。最近修订的 δ ¹³ C-CH ₄与 δ ² H-CH _{4 的}遗传图和其他参数，如气体干度比和水化学，证实了生物成因是主要的气体来源。二氧化碳和甲烷之间的碳同位素差异（Δ ¹³ C _H2O–CH4），以及水和甲烷中的氢同位素差异（Δ ² H _H2O–CH4），也表明典型的微生物 CO ₂还原途径。溶解无机碳的正碳同位素组成(δ ¹³C-DIC) 不仅显示出煤层气井水与浅层含水层水之间的明显区别，而且证实了与高碱度配对时产甲烷的发生。此外，水质分析显示钠和碳酸氢盐浓度随深度增加，这是煤层气生产盆地的典型特征。尽管确定了生物成因气体，但构造环境似乎不能解释气体成因的发生，因为预计二次生物发生在诸如 Cesar Rancheria 的隆起盆地中。同位素数据在区分原生生物成因和次生生物成因方面并不是决定性的，因为气体同位素组成绘图靠近原生和次生生物气田之间的边界。