大宁-吉县地区煤系叠置含气系统地球化学特征及其对成藏过程的响应

Coal-bearing seam ‘three gas’ resources which were characterized by the symbiosis of coalbed methane, tight sandstone gas and shale gas have been a hot point in the exploration and development of coal-bearing seam in China in recent years. After years of production，it showed that the gas source of the gas system in coal-bearing seams is very complex with multisource. There is a strong connection between the gas accumulation processes of coal bed methane, tight sandstone gas and shale gas. Many sets of superimposed and symbiotic fluid pressure systems are developed in coal-bearing strata. Affected by the differences in energy and physical properties between these superimposed CBM-bearing gas systems, it is very difficult for CBM commingled development. However, the study on relationships between coal-bearing seam ‘three gas’ (coalbed methane, tight sandstone gas and shale gas) during gas accumulation process is relatively poor..This project will focus on gas geochemical characteristics of superimposed CBM-bearing system in coal measures and their indication to gas accumulation process in Daning-Jixian region. Firstly, by studying geochemistry character of coalbed methane, shale gas and tight sandstone gas in each reservoir, the differences and connections of gas geochemical characteristics between three coal-bearing seam gas reservoirs systems will be analyzed. Then, the reservoir energy compatibility between superimposed gas systems will be discussed. Combing with results of organic matter thermal evolution experiments, the gas distribution process (generation, dissipation and migration) between ‘three gas’ reservoirs will be investigated. Finally, the symbiosis mechanism of gas accumulation in superimposed coal-bearing seam will be revealed.

以煤层气、致密砂岩气和页岩气共生为特征的煤系“三气”资源是近年来我国含煤地层资源勘探开发的热点。多年开发实践研究表明煤系气具有多源性，煤层气、致密砂岩气和页岩气之间关系密切。煤系地层内部多套流体压力系统叠置共生且含气系统之间的能量与物性差异性大导致了“三气”共采兼容性问题突出，严重影响了煤系气资源的共探共采。然而，针对煤系“三气”气源内在联系的研究相对较少。.本项目拟以大宁-吉县地区为重点研究区块，针对“煤系叠置含气系统的气体地球化学特征及其对‘三气’成藏过程的响应”这一核心问题开展研究，分析不同煤系气储层之间气体地球化学特征的差异与联系，探讨叠置系统之间能量系统的兼容性。结合热演化模拟实验结果，综合研究煤系地层各储层间气体生成与运移等配置过程，最终揭示煤系气储层“三气”叠置共生成藏机理。

以煤层气、致密砂岩气和页岩气共生为特征的煤系“三气”资源是近年来我国非常规油气勘探开发的热点。多年开发实践研究表明煤系气具有多源性，煤层气、致密砂岩气和页岩气之间关系密切。煤系地层内部多套流体压力系统叠置共生且含气系统之间的能量与物性差异性大导致了“三气”共采兼容性问题突出，严重影响了煤系气资源的共探共采。然而，针对煤系“三气”气源内在联系的研究相对较少。.本项目以大宁-吉县地区为研究区块，针对“煤系叠置含气系统的气体地球化学特征及其对‘三气’成藏过程的响应”这一核心问题开展研究。采用气体组分、甲烷、乙烷碳氢同位素、地层水氢氧同位素、岩性样品成熟度实验，分析不同煤系气储层之间气体地球化学特征的差异性，揭示了大宁-吉县地区“三气”地球化学特征差异性地质控制机理。基于成烃热演化模拟实验结果，建立了煤系地层有机质（煤、页岩）热演化地球化学特征模式。基于流体包裹体实验完成了致密砂岩气主排烃充注时期解剖，结合区域成藏演化史数值模拟，厘定区域煤系“三气”主“生-排-聚”期次。煤系气烃源岩主生烃期为早白垩世早期，主排烃-充注-聚集期为早白垩世晚期。应用煤系地层有机质（煤、页岩）热演化地球化学特征识别模式，将现今“三气”储层地球化学特征与模拟实验内有机质地球化学指标（烃源岩、气态产物）阶段性特征对应，确立煤储层、页岩储层以及致密砂岩层之间的相关性。剖析煤系“三气”烃源岩（煤岩、页岩）与储层（煤岩、页岩、致密砂岩）之间气体的配置过程（运移的时间、方向、通道），最终揭示了煤系气储层“三气”叠置共生的成藏机理。提出“源內成藏、近源成藏和远源成藏”三种类型气藏“生储盖”组合模式。