煤层气井产出水化学特征及水化学场动态演化规律

Hydrochemical characteristics and dynamic evolution of hydrochemical field for the produced water of CBM wells

为查明煤层气井产出水的化学特征及水化学场动态演化规律,对沁水盆地南部多口煤层气井产出水进行连续长期的水化学场检测,通过对比3号和15号煤层产出水离子浓度的变化以及各离子之间、同位素的相关关系,发现3号和15号煤层产出水阳离子主要为Na++K+,阴离子以HCO-3和Cl-为主,水化学类型均多为HCO3·Cl—Na型。p H范围为7.5～8.6。溶解性总固体最小为1 149.6 mg/L,最大达到3 617.4 mg/L。3号煤层产出水δD平均为-80.7‰,δ^(18)O平均为-10.4‰,15号煤层气井产出水中δD值平均为-83.6‰,而δ^(18)O值平均为-11.2‰。由δD和δ^(18)O之间的关系可以判断出两个煤层均受大气降水补给。且随着埋深的变浅,δD和δ^(18)O值显示出递增的趋势。由煤层水和临近含水层水的离子成分以及δD与δ^(18)O值对比,可以推测煤层的补给水源。通过产气量与产水量分析,得出溶解性总固体与产气量有明显的正相关关系,这对于产能预测有重要意义。

Continuous long-term hydrochemical field detection is carried out to the produced water from coal bed methane(CBM) wells in the southern Qinshui Basin.The chemical characteristics and dynamic evolution of hydrochemical field for produced water of CBM wells are summarized.For the produced water from the 3# and 15 # coalbeds,Na++ K+are the main cations and HCO-3 and Cl-are the main anions.The hydrochemical type is mainly of HCO3-Cl-Na type.The pH value ranges from 7.5 to 8.6 and the salinity,from 1 149.6 mg/L to 3 617.4 mg/L.For the 3# coalbed produced water,the average δD is about-80.7‰,and δ18O,-10.4‰.For the 15 # coal bed produced water,the average δD is about-83.6‰,and δ18O,-11.2‰.The relation between δD and δ18O indicate that the groundwater from the two coalbeds is of meteoric origin.The values of δD and δ18O decrease with the increasing buried depth.We can determine the supplying aquifer of the coalbed through comparing the ion compositions and the values of δD and δ18O between the coalbed water and its adjacent groundwater.There is a positive correlation between the salinity and gas production via analysising the gas production and water yield.The results are of great significance in the prediction of gas production.