Investigation of the temperature effect on rock permeability sensitivity

The temperature effect on rock physical properties, including permeability, is still topical, since the available findings are quite contradictory. In the current study of temperature effect on rock permeability, the experiments have been conducted on eight rock samples of different permeability (4) and lithology (4). The results obtained strongly indicate that the temperature effect depends on the initial permeability of core samples: for low-permeability (LP) or higher-permeability (HP) rocks, the temperature-permeability dependence exhibits a negative nonlinear correlation. When the temperature increases from 20 degrees C to 100 degrees C, the permeability of LP rocks decreases by 24-70%. However, in ultra-LP rocks, a positive nonlinear correlation has been revealed between temperature and permeability: when the temperature was increased from 100 to 800 degrees C, the permeability of ultra-LP rocks exhibited a gradual increase within the initial range from 200 degrees C to 400 degrees C, and a sharp rise, while in the medium range from 400 to 600 degrees C the lithology threshold value was reached, the thermal-induced tensile stress in the rock exceeded its yield stress, which resulted in a sharp increase of permeability in the final temperature range from 600 to 800 degrees C. Based on the experimental data obtained in this study, a theoretical model is proposed, which implies a positive correlation between rock permeability, pressure, and temperature.