页岩孔隙空间的形成与演化及孔隙对含气性的影响

虽然页岩气的勘探已经在北美以及中国取得了突破，但是对页岩中孔隙空间的形成与发育仍然存在较大的争议，页岩中是否存在有效的孔隙，这些孔隙与气体的赋存有何联系都需要解答。本文对不同地区、不同岩石类型以及不同热成熟度的页岩进行微观分析，对比前人的研究，同时结合四川盆地龙马溪组页岩的实际分析数据，将页岩划分为富有机质页岩和含粉砂质泥页岩。富有机质页岩中有机质纳米孔是主要的孔隙类型，同时也是气体聚集与吸附的主要空间，有机质孔隙度与有机质含量、热成熟度密切相关；含粉砂质泥页岩中以粒间、粒内溶蚀孔为主，由于有机质含量较少，因而受热成熟影响很小。对页岩的孔隙形成机理分析发现，富有机质页岩孔隙度与有机质含量呈正相关，特别是与初始有机碳含量密切相关，因此恢复初始有机碳的含量是评价页岩含气量与含气性的关键。在热演化程度较低时（Ro < 0.6%），页岩中有机质孔隙不发育，页岩几乎不含气；随着热演化程度升高（Ro = 0.8%），页岩微孔隙发育，此时页岩以吸附气为主；随着热演化程度增大（Ro > 1.2%），微孔逐渐向中孔和宏观孔转化，总的比表面积减小，页岩中游离气含量开始增加，吸附气含量减少。

The formation and evolution of shale pore space and pore effects to gas bearing capacity

The exploration of shale gas has been shown to be successful in North America and China. However，some controversy on the pore space and its formation still surrounded it. It is still not clear that whether the shale contain effective pores and how these pores influence the occurrence states of shale gas. To answer these questions，based on research achievements of preceding scholars and our experiments data of Longmaxi shale in Sichuan Basin，study is carried out on shale microscopic analysis of different areas，different rock types and different thermal maturities in this article. As a result，firstly，shale is classified in to organic-rich shale and silty-clay shale. Secondly，to organic-rich shale，the development of nanopore in organic matter （OM），the principal pore as well as the assemble and absorbed space of gas，is controlled by TOC content，especially the initial organic carbon content，so recovering the initial organic carbon is the critical factor for evaluating the gas resources in the shale. Thirdly，in low-maturity phase （Ro < 0.6%），there is no shale gas because OM pores is absent. With the shale developing to maturity phase （Ro = 0.8%），OM’s nanopores are abundant and shale gas is absorbed in them. As the maturity growing up to Ro > 1.2%，the micropore conver to mesoporous and macroporous pores，the specific surface areas decrease and the absorbed gas lessen，free gas content gets to increase.