摘要
准噶尔盆地南缘部分地区低阶煤储层中CO_(2)的富集,不仅反映了煤层气系统形成和改造过程受多元干预作用,也影响到煤层气资源的品质。为查明该区煤层中富CO_(2)低阶煤层气藏形成机制,基于煤层气排采井气样,开展了煤层气地球化学研究。结果显示:准南地区煤层甲烷碳、氢同位素整体上偏轻,δ(13)C_(CH_(4))为-6.82%~-4.38%,δ(13)D_(CH_4)为-29.00%~-30.41%;米泉地区煤层气以生物成因气为主,四工河及玛纳斯地区深部煤层主要发育热成因气,白杨河地区则以混合成因气为主;准南地区煤层气中CO_(2)浓度差异大,多元地质因素干预明显,二氧化碳碳同位素偏重,δ(13)C_(CO_(2))为-1.54%~2.51%,CO_(2)来源主要为煤化作用初期热解和微生物成烃伴生。地下水动力条件是决定CO_(2)富集的关键因素,煤化作用初期生烃阶段产生的CO_(2)在滞流条件下聚集,微生物作用伴生CO_(2)在弱径流条件下混入保存;煤层自燃致使烧变岩系发育,进而地表水下渗作用增强所引起的非烃类气体参与煤层气成藏,则符合真正意义上煤层气风氧化作用机制。综合研究认为,差异性地层水溶解消耗作用以及生物成烃改造作用主要影响煤层CO_2的分布特征,煤层气成藏过程中存在的CO_(2)干预作用形成了封闭滞流原位型、半封闭扰动型以及开放连通型三类煤层气藏,承载着煤层气成因、煤层气藏赋存特征等信息。
The low-rank coalbed methane(CBM)reservoirs in part of the southern Zhunggar Basin has higher CO_(2) enrichment degree,which not only reflects the multiple intervention in the process of formation and transformation of CBM system,but also affects the quality of CBM resources.To find out mechanism on the formation of CO_(2)-enriched coalbed methane reservoirs,geochemical research was carried out based on gas samples from production wells.The results indicate that the carbon isotope(δ13CCH4=-7.83%~-4.06%;δ13DCH4=-29.00%~-30.41%)of methane is generally lighter.The Miquan and Baiyanghe areas are dominated by biogenic gas and mixed causative gas,respectively,while the deep seams in Sigonghe and Manasi areas mainly developed thermally derived gas.There are significant vertical variations in CO_(2) concentration,with obvious multiple geological factors intervention phenomena.Isotope analysis suggested thatδ13CCO_(2) is generally heavier(δ13CCO_(2)=-1.54%~2.51%).The sources of CO_(2) are mainly from the pyrolysis at the beginning of coalification and microbial hydrocarbon generation.Hydrodynamic conditions played an important role in CO_(2) enrichment:the CO_(2) generated in the early hydrocarbon generation stage of coalification accumulates at stagnant condition.The associated CO_(2) of microbial action mixed and preserved under weak runoff conditions.The spontaneous combustion of coal seams leads to the development of burnt rocks and the enhanced underwater seepage,which resulted the participation of non-hydrocarbon gases in the formation of CBM.It is in line with the affected of CBM wind oxidation.Comprehensive analysis shows that the differential groundwater dissolution and bio-hydrocarbon reformation affected the distribution characteristics of CO_(2) in coal seams.CO_(2) intervention formed the closed-stagnant-in-situ,semi-closed perturbed,and open connected coalbed methane reservoirs,which carries key information such as the origin and the occurrence of coalbed methane resources.
作者
李站伟
汤达祯
唐淑玲
蒲一帆
张奥博
LI Zhanwei;TANG Dazhen;TANG Shuling;PU Yifan;ZHANG Aobo(School of Energy Resources,China University of Geosciences(Beijing),Beijing 100083,China;Coal Reservoir Laboratory of National Engineering Research Center of Coalbed Methane Development&Utilization,Beijing 100083,China;Beijing Key Laboratory of Unconventional Natural Gas Geological Evaluation and Development Engineering,Beijing 100083,China)
出处
《煤炭科学技术》
CAS
CSCD
北大核心
2021年第3期175-180,共6页
Coal Science and Technology
基金
国家科技重大专项资助项目(2016ZX05043-001)
国家自然科学基金面上资助项目(41772132)
