柴北缘盆地YQ-1井中侏罗统石门沟组泥页岩纳米孔隙特征及影响因素

Characteristics and influencing factors of nanopores in the Middle Jurassic Shimengou shale in well YQ-1 of the northern Qaidam Basin

柴达木北缘（柴北缘）盆地侏罗纪是典型的陆相湖沼盆地,是目前具有页岩气潜力的盆地之一。本文运用氮气吸附、有机碳含量、有机质成熟度、全岩X衍射分析等方法,对柴北缘鱼卡地区YQ-1井中侏罗统石门沟组泥页岩的纳米孔隙特征及控制因素进行研究。结果表明,石门沟组泥页岩纳米孔隙结构复杂,根据吸附回线及孔径分布特征可划分为两类,第一类以一端不透气性孔和开放性平行板状狭缝孔为主,孔径主要集中在3~5nm范围内,呈单峰状分布;第二类则以一端不透气性孔和开放性倾斜板狭缝孔为主,孔径主要分布在3~5nm和8~14nm范围内,呈双峰状分布。孔径小于50nm的微孔和介孔是比表面积和孔体积的主要贡献者;黏土矿物含量与微孔、介孔、总孔体积呈正相关;在较低的成熟度制约下,泥页岩有机质孔隙基本不发育,有机质丰度较高的石门沟组上段H9泥页岩TOC含量与微孔、介孔、总孔体积呈负相关性,有机质丰度较差的下段H8泥页岩TOC含量与孔体积相关性则不甚明显;孔隙结构及孔径分布受沉积环境水动力条件影响;黏土矿物是石门沟组泥页岩纳米孔隙的主要提供者,是孔隙发育的主控因素,TOC含量与沉积环境也会对泥页岩孔隙发育产生一定影响。

The Northern Qaidam Basin（NQB）is a typical continental limnic basin and is also one of the basins with most shale gas potential.In this paper,the characteristics and influencing factors of nanopores of the shales in the Middle Jurassic Shimengou Formation of Well YQ-1in the Yuqia area of NQB were studied by using nitrogen gas adsorption,total organic carbon content,organic matter maturity,and X-ray diffraction analyses.The results showed that the nanopore structures in the Shimengou shale are complex,and these nanopores can be subdivided into two types based on the nitrogen adsorption-desorption curves and pore diameter distribution.The first type mainly consists of the airtight pores with one end closed and the open parallel plate-slit pores,and the pore diameters are in a range of 3-5nm.The second type mainly consists of the airtight pores with one end closed and the open inclined slit pores,and the pore diameters are characterized by a bimodal distribution,peaking in a range of 3-5nm and 8-14 nm.The micropore and mesopore with an aperture smaller than 50 nm provided the dominating specific surface area and pore volume.The volume of micropores,mesopores and total pores showed a positive correlation with the clay contents.The pores of organic matter were less developed at a low maturity.The H9 shale,characterized by a high TOC content,shows a negative correlation between the TOC content and the volume of micopores,mesopores and total pores,while the H8 shale,characterized by a low TOC content,shows no correlation.Pore structures and diameter distributions are related to the hydrodynamic conditions of depositional environment.The clay content is a key factor controlling the nanopore development in shale,and the TOC content and depositional environment also have a certain influence.