不同沉积类型富有机质页岩孔隙结构差异特征

Characteristics of pore structure differences of organic-rich shale in different sedimentary types

四川盆地页岩气勘探开发取得巨大成效,不同沉积类型的富有机质页岩孔隙结构不清,制约了四川盆地页岩气进一步的勘探开发。选取四川盆地龙马溪组海相页岩、龙潭组海陆过渡相页岩、自流井组陆相页岩TOC>1%的富有机质页岩样品,通过场发射扫描电子显微镜和高压压汞结合的方法,了解了不同沉积类型页岩孔隙结构的差异。结果表明,龙马溪组海相页岩主要发育有机质孔和黄铁矿晶间孔,有机质孔多呈圆形、椭圆形,黄铁矿晶间孔形态不一,以大于100 nm的孔隙为主;自流井组陆相页岩主要以原生粒间孔、晶间孔为主,多呈狭缝形、楔形,孔径主要集中在<15 nm区间内;龙潭组海陆过渡相页岩主要发育微裂缝原生粒间孔、晶间孔,原生粒间孔、晶间孔多呈狭缝形,孔隙主要集中在30~120 nm和250~1300 nm两个区间。有机质和矿物组成的原始差异以及在页岩沉积埋藏过程中热演化和成岩演化的不同是孔隙结构产生差异的主要原因。

Great achievements have been made in exploration and development of shale gas in Sichuan Basin.The unclear pore structure of organic-rich shale in different sedimentary types restricts the further exploration and development of shale gas in Sichuan Basin.The marine shale samples of Longmaxi Formation,transitional shale of Longtan Formation,and continental shale of Ziliujing Formation in Sichuan Basin were selected.The differences in pore structure of shale in different sedimentary types were defined by field emission scanning electron microscope and high-pressure mercury injection.The results show that the marine shale of Longmaxi Formation mainly developed organic pores and intercrystalline pores of pyrite.Most of the organic pores were round and elliptic,and the intercrystalline pores of pyrite were of different shapes.The pores were generally larger than 100 nm.The continental shale of Ziliujing Formation was mainly composed of primary intergranular pores and intercrystalline pores,which were mostly in slit shape and wedge shape.The pore sizes were mainly within<15 nm.In the transitional shale of Longtan Formation,primary intergranular pores and intercrystalline pores with micro-fractures were mainly developed.The primary intergranular pores and intergranular pores were mostly slit shaped,and the pores were mainly concentrated in two intervals of 30~120 nm and 250~1300 nm.The primary differences of organic matter and mineral composition and the differences of thermal and diagenetic evolution during shale deposition and burial were the main reasons for the differences of pore structure.