深井温湿环境下泥页岩力学特性及微观孔隙结构演化机制

Mechanical properties and microscopic pore structure evolution mechanism of shale under deep well temperature and humidity environment

微观孔隙结构对页岩油气藏的勘探利用具有重要意义。以松科二井深层泥页岩试样作为研究对象,进行了热、液作用下的泥页岩力学特性和孔隙变化研究。采用场发射扫描电镜(SEM)、高压压汞、CT扫描等实验方法,对饱和和加热处理的泥页岩进行了微观孔隙特征对比研究。结果表明:该泥页岩试样主要孔隙类型包括微裂隙、粒间孔、粒内孔等,其中发育较多的微纳米缝,主要尺寸区间为20~400 nm;饱和湿度、高温加热均会降低泥页岩的孔容、孔隙率以及渗透率,且温度越高影响越明显,饱和试样纳米级孔隙收缩减小,1~35μm占比增多,大于35μm孔隙占比减少,内部宏观裂缝被吸水膨胀矿物填充;加热试样纳米级孔隙向两侧开裂,40~100 nm孔隙转化为数百纳米甚至微米级孔隙,1~50μm孔隙占比增加,内部宽大裂缝被填充形成细小圆孔裂缝。同时借助计算机软件对CT扫描所获取的泥页岩样品进行三维孔隙模型的重建,以提供更加清晰、逼真的立体化展示和对泥页岩表面及内部微观孔隙进行定量研究。

Microscopic pore structure is of great significance to the exploration and utilization of shale oil and gas reservoirs.Taking the deep shale samples of Songke No.2 well as the research object,the mechanical properties and pore changes of shale under the action of heat and liquid were studied.The microscopic pore characteristics of saturated and heated shale were compared by means of field emission scanning electron microscopy(SEM),high pressure mercury injection and CT scanning.The results show that the main pore types of the shale samples include micro‑cracks,intergranular pores,intragranular pores,etc.,among which more micro‑nano cracks are produced,and the main size range is 20~400nm.The saturated humidity and high temperature heating will reduce the pore volume,porosity and permeability of shale,and the higher the temperature,the more obvious the effect.The nano‑scale pore shrinkage of saturated samples decreases,the proportion of 1μm-35μm increases,the proportion of pores larger than 35μm decreases,and the internal macro‑fractures are filled with water‑absorbing expansive minerals.The nano‑scale pores of the heated sample crack to both sides,and the 40nm-100nm pores are converted into hundreds of nanometers or even micron‑scale pores.The proportion of 1μm-50μm pores increases,and the internal wide cracks are filled to form small round‑hole cracks.At the same time,the three‑dimensional pore model of the shale samples obtained by CT scanning is reconstructed by computer software to provide a clearer and more realistic three‑dimensional display and quantitative study on the surface and internal micro‑pores of shale was carried out.