砂岩渗透参数随渗透水压力变化的CT试验

Permeability experiment of sandstone under variable seepage pressures by using X-ray CT real-time observation

运用岩石高压三轴加载装置和渗透压加载装置,对砂岩进行固定应力变渗透水压力试验,同时借助SOMATOMPLUS螺旋CT扫描机进行实时观测。通过试验结果分析,推出了基于CT数的岩石空隙率计算公式,从CT尺度上分析了岩石空隙率、渗透速度、渗流速度、微孔隙直径、渗透率等随渗透水压力的变化规律,结果表明:岩石的渗透参数(空隙率、微管径、渗透率)随渗透水压力的增加而增大,渗透参数随渗透水压力的变化呈对数关系,这是由于渗透水压力使岩石内部空隙发生变形,从宏观应力-应变关系看,岩石并未出现宏观破坏,还处于弹性变形阶段;而渗流速度与渗透水压力呈线性关系,符合宏观尺度渗流的达西定律。

The seepage experiment of a sandstone sample under constant compressive stress was conducted in the laboratory using triaxial loading apparatus, seepage pressure loading apparatus and medical SOMTOM-plus CT scanner. Having analyzed the results of this experiment, the porosity formula of rock based on CT number was proposed in CT scale, and the variations of the porosity, the real flow rate in porous rock, the specific discharge, permeability and the micro-pore diameters with increasing seepage pressures were studied. The results show that the seepage parameters, such as porosity, micro-pore diameters and permeability, increase with the increase of seepage pressures. Logarithm relations between the seepage parameters and seepage pressures were proposed. The seepage pressures made the micro-pores of rock enlarged. It is shown by the relation between stress and strain of a rock in macro-scale that there is no macro-crack in the rock samples. Therefore, the deformation of rock induced by seepage pressures is elastic before macro-crack occurs. The relation between the specific discharge and seepage pressure is linear and consistent with the Darcy law in macro-scale.