摘要
研究页岩脆性成因对于深入认识页岩气成藏规律具有重要的意义,但目前的研究大多集中在生物石英富集提高页岩的脆性方面,而对于成岩演化过程中石英的重结晶作用则认识不足。为此,以四川盆地长宁区块下志留统龙马溪组海相页岩为例,借助阴极发光、扫描电镜等仪器对页岩孔隙、矿物组成、层理特征等进行观察,通过分析页岩矿物组构特征和硅质组分镜下特征,研究石英来源、超压环境及成岩演化对页岩脆性的控制作用,提出了海相页岩自生脆化作用的形成模式,阐述了成岩过程中自生微晶石英对提高页岩脆性的地质意义。研究结果表明:(1)页岩在其沉积、埋藏、成岩演化过程中发生成岩变化,提高了石英含量,形成隐伏缝网,有利于后期改造形成复杂流通通道;(2)有机质在地质演化过程中对于提高页岩脆性发挥了正向促进作用,促进了自生微晶石英形成,提高了页岩脆性。结论认为:(1)页岩成岩演化中发生的页岩自生脆化作用改变了岩石结构,增加了岩石强度,保存了页岩的孔隙性,改善了页岩的储集空间,改变了页岩气富集状态,使构造运动因素下控制的保存条件评价成为页岩气地质评价的关键因素;(2)海相页岩只要有机质含量丰富,经过成岩过程中的自生脆化机制必定形成良好的脆性。
Studies on the origin of shale brittleness are of great significance to understanding shale gas accumulation laws. The current studies, however, mostly focus on the improvement of shale brittleness by biological quartz enrichment, but rarely on the recrystallization of quartz in the process of diagenetic evolution. In this paper, a series of researches were carried out on the Lower Silurian Longmaxi Fm marine shale in the Changning block of the Sichuan Basin. Firstly, shale pore, mineral component and bedding characteristics were observed by means of cathodoluminescence（CL）, scanning electron microscope（SEM） and so on. Then, the control effects of quartz origin, overpressure environment and diagenetic evolution on shale brittleness were investigated by analyzing the mineral composition and siliceous composition of shale microscopically. Finally, the authigenic embrittlement model of marine shale was put forward and the geological significance of authigenic microcrystalline quartz to the improvement of shale brittleness in the process of diagenesis was illustrated. The following results were obtained. First, during the sedimentation, burial and diagenetic evolution, shale experiences diagenetic changes which help increase quartz content and form concealed fracture networks, thus benefiting the formation of complex flow pathways in later stimulation. Second, organic matters play a positive role in improving shale brittleness in the process of geological evolution. It promotes the formation of authigenic microcrystalline quartz and improves the brittleness of shale. In conclusion, due to the authigenic embrittlement of shale in the process of diagenesis, rock structure is changed, rock strength is enhanced and shale porosity is preserved. Consequently, reservoir space in shale is improved and the enrichment state of shale gas is modified. Therefore, the preservation condition under the control of tectonic movement factors is vital to geological evaluation on shale gas. In addition, marine shale is certainly well brittle after authigenic embrittlement in the process of diagenesis as long as its organic matter content is abundant.
作者
刘洪林
郭伟
刘德勋
周尚文
邓继新
Liu Honglin;Guo Wei;Liu Dexun;Zhou Shangwen;Deng Jixin(PetroChina Research Institute of Petroleum Exploration ＆ Development, Langfang, Hebei 065007, China;Chengdu University of Technology, Chengdu, Sichuan 610059, China)
出处
《天然气工业》
EI
CAS
CSCD
北大核心
2018年第5期17-25,共9页
Natural Gas Industry
基金
国家科技重大专项"四川盆地及周缘页岩气形成富集条件
选区评价技术与应用"(编号:2017ZX05035)
关键词
海相页岩
石英
重结晶
自生脆化作用
隐伏缝网
脆性提高
四川盆地
长宁区块
早志留世
龙马溪组
Marine shale
Quartz
Recrystallization
Authigenic embrittlement
Concealed fracture network
Brittleness improvement
Sichuan Basin
Changning block
Early Silurian
Longmaxi Fm
