同沉积期火山活动对华南五峰组-龙马溪组页岩气源-储品质的影响

Wufeng Formation-Longmaxi Formation in South China, which are the key strata achieving significant breakthrough in shale gas exploration, contain widespread K-bentonite layers representing frequent volcanic activities occurred in sedimentary period. High quality productive layers of domestic and foreign shale oil-gas deposited accompanying volcanic ash beds normally, which indicated intimate relationship existing between synsedimentary volcanism and shale oil-gas accumulation. However, systematic research into volcanic influence on organic generation and preservation in shale gas source rock is insufficient, and it is still unclear about volcanic influence on pore features in shale gas reservoir. Therefore, Wufeng Formation-Longmaxi Formation in South China have been selected as studied object to analyze effect of synsedimentary volcanism on shale gas source rock and reservoir. Initially, it is necessary to analyze the volcanic influence on organic generation and preservation, through quantitative estimation of productivity, identification and quantitative statistics of microorganisms, recovering marine anoxia model in sedimentary period. Then, volcanic effect on pore features in shale gas reservoir need to be estimated, through studying characteristics and origin of reservoir pores. This research will contribute to understand volcanic effect on generation and accumulation of shale gas, and to confirm main controlling factors of shale gas content. On this basis, it will provide theory basement for predicting shale gas dessert area, and evaluating resource potentials of shale gas in other regions or other strata.

华南地区五峰组-龙马溪组是我国页岩气勘探突破的重点层系，其中广泛发育的钾质斑脱岩层，代表沉积时期存在频繁的火山活动。国内外页岩油气优质产层大多伴生火山灰层，可见同沉积期火山活动与页岩油气的富集具有密切关系。然而，火山活动对页岩气烃源岩中有机质形成与保存的影响缺乏系统的研究，对页岩气储层孔隙特征的影响尚不明确。因此，本次研究计划以五峰组-龙马溪组为研究对象，分析沉积期火山活动对页岩气源岩与储层的影响。首先，通过定量估算生产力、鉴定微生物种类与统计数量、恢复沉积期海洋缺氧模式等，判断火山活动对有机质形成与保存的作用。其次，通过统计火山作用下储层孔隙特征及其成因等，分析火山活动对储层孔隙的影响。此研究有助于理解火山活动对页岩气形成与富集的作用机制，明确页岩含气性主控因素，进而为甜点区预测，以及其他地区或层系页岩气资源潜力评价提供理论依据。

华南地区五峰组-龙马溪组页岩沉积过程中伴随着大量火山活动导致的斑脱岩沉积，然而火山活动对页岩气烃源岩与储层质量的影响尚未明确。本次研究通过分析研究区五峰组-龙马溪组页岩的岩石学、地球化学、储层学、含气性等数据，系统分析了其沉积时期火山活动对页岩有机质形成与保存的影响，以及对页岩气储层孔隙特征与可压裂性的控制作用。通过分析获得以下主要认识：（1）华南地区五峰组-龙马溪组沉积期的火山活动喷发出的大量营养物质，使水体中疑源类为主的浮游藻类迅速繁盛，为有机质的富集提供了物质基础。此外，火山喷发出的CO2与H2S等气体，导致水体中缺氧程度加剧，有助于有机质的保存。（2）由于火山活动使水体中浮游藻类比例增加，不仅增加了页岩储层中的有机质含量，浮游藻类成烃生物相比于底栖生物，形成的有机质孔隙孔径较小，但连通性较好且比表面积较高，导致火山活动频繁时期形成的页岩储层具有较高的含气性。并且，火山活动使硅质放射虫等含硅生物大量繁盛，其埋藏后导致页岩中生物成因硅含量较高，使页岩储层的脆性增加，在压裂过程中易形成复杂网缝。因此，同沉积期火山活动有利于页岩气优质烃源岩的形成，并可提高页岩储层储气能力与可压裂性。国内外页岩油气优质产层大多伴生火山灰层，此研究初步明确了火山活动对页岩气形成与富集的控制作用，可提高华南地区页岩气甜点区与有利层段预测准确性，并可为其他地区或层系页岩油气资源潜力评价提供理论依据。