The hydrogeochemical characteristics of coalbed-produced water can provide insights into the sources of ions and water, the groundwater environments, hydrodynamic conditions, and water-rock interactions of depositional basins. To study the water-rock reaction process and reveal whether there is a microbial activity in the groundwater, a case of the Dafosi biogenic gas field was chosen by testing the ionic concentrations and hydrogen and oxygen isotopic compositions of coalbed-produced water and employing R-type cluster and principal component analyses. The results showed that Na⁺, , and HCO₃^- are the principal ions in the coalbed-produced water, while the water type is mainly a Na–Cl. Due to the hydrolysis of HCO₃^-, the pH in this region was controlled primarily by HCO₃^-. As the main cation in water, Na⁺ contributed substantially to the total dissolved solids. Na⁺ is also related to the exchange between rock-bound Na⁺ and Ca²⁺ and Mg²⁺ in water or surrounding rocks. The coalbed-produced water’s oxygen isotopes displayed a characteristic ¹⁸O drift and enrichment, indicating that the ¹⁶O isotope in the water was preferentially exchanged with the coal organic matter. Early evaporation is also contributed to the enrichment of TDS (total dissolved solids) and ¹⁸O in the water. The central part of the study area, including the Qijia anticline, was affected by the Yanshanian uplift and denudation and subsequently developed a water-conducting fissure zone and was recharged atmospheric precipitation; these conditions were conducive to the formation of secondary biogenic gas.

中文翻译：

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鄂尔多斯盆地南缘大佛寺生物气田煤层采出水水文地球化学特征及水-岩相互作用

煤层采出水的水文地球化学特征可以深入了解离子和水的来源、地下水环境、水动力条件和沉积盆地的水-岩相互作用。为研究水-岩反应过程，揭示地下水中是否存在微生物活动，以大佛寺生物气田为例，通过测试煤层采出水的离子浓度和氢氧同位素组成，采用R-类型聚类和主成分分析。结果表明，Na ⁺、、 HCO ₃ ^-是煤层采出水中的主要离子，而水的类型主要是Na-Cl。由于 HCO ₃的水解^-，在这个区域中的pH通过HCO主要控制₃ ^- 。作为水中的主要阳离子，Na ⁺对总溶解固体有很大贡献。Na ⁺还与岩石中Na ⁺和Ca ²⁺和Mg ²⁺在水或围岩中的交换有关。煤层采出水的氧同位素表现出特征性的¹⁸ O漂移和富集，表明水中的¹⁶ O同位素优先与煤有机质交换。早期蒸发也有助于 TDS（总溶解固体）和¹⁸在水中哦。研究区中部包括齐家背斜在内，受燕山期隆起剥蚀影响，发育导水裂隙带，大气降水补给；这些条件有利于次生生物气的形成。