温度和有效应力对砂岩渗透率的影响机理研究

MECHANISM OF EFFECTS OF TEMPERATURE AND EFFECTIVE STRESS ON PERMEABILITY OF SANDSTONE

为探讨温度和有效应力,尤其是温度对渗透率的影响机理,在不同温度水平和不同有效应力水平下,分别进行了砂岩的孔隙度试验和渗透率试验。试验结果表明:在温度水平一定的情况下,砂岩岩样的孔隙度和渗透率均随有效应力的增加而减小,但孔隙度的减小幅度大大小于渗透率的减小幅度;而在有效应力水平一定的情况下,当温度升高时,砂岩岩样的渗透率减小幅度很大,但孔隙度的变化却很小。通过对试验结果的分析,初步提出了温度和有效应力对砂岩渗透率的影响机理。就本试验所用砂岩而言,有效应力对渗透率的影响主要在于有效应力对孔隙,尤其是对喉道的压缩作用;而温度对渗透率的影响则主要在于随温度升高而加剧的粘土矿物的分散作用(可能也是更为重要的原因)以及砂岩骨架的热膨胀对喉道的压缩作用。

In order to study the mechanism of the effect of temperature and effective stress on permeability, the porosity and permeability tests for sandstone were conducted at various temperature and effective stress levels. The test results show that both the porosity and permeability of sandstone samples decrease with the increasing effective stress at a fixed temperature level, but the decreasing extent of porosity is much smaller than that of permeability. At a fixed effective stress level, when temperature increases from 20°C to 60°C, the decreasing extent of the permeability of sandstone samples is about 55.81%-73.85%, but the variation range of porosity is less than 3%. According to the analysis of test results, the mechanism of the effect of temperature and effective stress on the permeability of sandstone is proposed. As far as the sandstone concerned, the effect of effective stress on permeability lies in pressure effect of effective stress on pore, especially on throat, and that of temperature lies in aggravating disaggregation of clay mineral with rising temperature and pressure effect of skeleton expansion on throat. The disaggregation of clay mineral is probably the most important factor.