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为了观察和度量岩石空隙结构随应力的变化,研制一种能和微焦X射线CT系统配套使用的三轴仪,该设备轻便,能够施加三轴压力,并在不卸载压力情况下对试样进行CT扫描和渗透系数的测量,且能够实时记录压力和变形等数据。利用研制的CT三轴仪得到了Berea砂岩在加载过程中的一系列CT图像,结合3DMA空隙结构计算方法,获得Berea砂岩在不同应力状态下的有效孔隙半径分布、有效喉道半径分布以及弯曲度分布等定量细观几何特征。同时采用瞬态脉冲法测量Berea砂岩不同方向的渗透率随有效围压的变化规律。结合围压对细观空隙结构参数的影响,认为细观空隙结构的变化是导致渗透发生改变的根本原因,当有效围压从0增至15 MPa时,半径40~100μm的孔隙数量减少、孔喉半径减小以及Z方向的迂曲度增加,是导致Berea砂岩渗透率随有效围压增大而降低的主要原因。
In order to observe and measure the variation of rock void structure with the stress, a triaxial apparatus which can be used with micro-focus X-ray CT system is developed. The apparatus is lightweight, capable of exerting triaxial pressure and testing the sample without unloading pressure CT scan and permeability coefficient measurements, and can record real-time pressure and deformation data. A series of CT images of Berea sandstone during loading were obtained by the developed CT triaxial apparatus. Combined with 3DMA calculation, the effective pore radius distribution, effective throat radius distribution and bending degree of Berea sandstone under different stress states were obtained. Distribution and other quantitative meso-geometry features. At the same time, the transient pulse method was used to measure the permeability of Berea sandstone in different directions with the variation of effective confining pressure. Combined with the effect of confining pressure on the parameters of mesostructured void, it is considered that the change of mesostructure is the fundamental reason for the change of permeation. When the effective confining pressure increases from 0 to 15 MPa, the number of pores with radius of 40-100 μm decreases, The decrease of throat radius and the increase of tortuosity in Z direction are the main reasons for the decrease of permeability of Berea sandstone with increasing effective confining pressure.