云南老厂雨汪煤层气区块气水成因及产能响应

为提高云南老厂雨汪区块煤层气(CBM)产能,基于6口煤层气先导试验井的气体样品组分、甲烷碳同位素、产出水氢氧同位素及微量元素测试结果,结合研究区煤层气地质条件和产能特征,分析了气体组分、水的氢氧同位素特征及微量元素成分对产能的指示意义。结果表明:研究区煤层气气体组分以CH₄为主,含少量C₂H₆、N₂和CO₂,不含重烃,为热成因气,并经过了后期的次生改造。煤层气井产出水的氢氧同位素特征说明产出水来源于大气降水,呈现明显的¹⁸O漂移特征。主成分分析结果显示产出水微量元素成分可以归纳为两个主成分,分别反映气井的产气和产水情况。根据煤层气井气水产出情况、产出水的氢氧同位素特征、微量元素成分综合分析表明,当前雨汪区块除LC-C3井外其他井产出水主要为压裂液,储层降压受限,导致气井产量较低。

Origin and Productivity Response of Gas and Water in Coalbed Methane Field of Yuwang Block at Laochang,Yunnan Province

To improve the productivity of coalbed methane (CBM) in Yuwang Block at Laochang(Yunnan province), we analyzed the composition of gas samples, methane, carbon isotopes, hydrogen-oxygen (H-O) isotopes of produced water and trace elements in 6 CBM pilot test wells, combined with the geological conditions and productivity characteristics of CBM. And we discussed the productivity indicating significance from isotopes and trace elements of the gas and water. The results show that CH₄ is the main component of local CBM, which accounts for over 97%. There are minor amounts of C₂H₆, N₂ and CO₂ but no heavy hydrocarbons, and the coalbed methane is mainly of thermal origin and has undergone later-stage secondary transformation. The H-O isotope characteristics of the CBM produced water indicate that the produced water was sourced from meteoric water, which show a clear ¹⁸O drift. The result of principal component analysis shows that trace elements in the produced water can be divided into two principal components, which reflect the gas and water production of gas wells, respectively. Integrating the comprehensive gas and water production, hydrogen-oxygen isotopes and trace elements data of the produced water from CBM wells, we suggested that the produced water of other wells in the Yuwang block is mainly fracturing fluid (except LC-C3 well), and that the reservoir pressure drop is limited, causing low gas well production.