Gas Klinkenberg effect of low-permeability rocks with different degrees of water saturation

The research on gas Klinkenberg effect of low-permeability rock is an important issue in the field of underground oil and gas storage, but the current one on gas Klinkenberg effect is most conducted under single-phase flow of gas, lacking in the research on the action of fluid on gas Klinkenberg effect under two-phase flow (gas-liquid) condition. Therefore, using the low-permeability rock permeability test system, the change laws of gas Klinkenberg effect and the effective permeability of low-permeability rocks with water saturations ranging from 0% to 70% are studied. The experimental results show that: (1) The quadratic formula k_g=k_∞(1+b/q-a/p²) can accurately interpret the gas Klinkenberg effect of low-permeability rocks, and its accuracy is significantly higher than that of the Klinkenberg equation. (2) The water saturation of low-permeability rocks has significant effects on the Klinkenberg effect. The gas Klinkenberg effect decreases as the water saturation increases, and the gas Klinkenberg effect is completely limited when the water saturation is more than 50%. (3) Owing to the effect of water, the gas Klinkenberg effect of water-filled low-permeability rocks declines with the increase of confining pressure, and it is opposite to the Klinkenberg's theory. (4) The water saturation has significant effects on the effective permeability of low-permeability rocks. The effective permeability decreases along with the increase of water saturation, and the sensitive degree of the effective permeability of low-permeability rocks to water saturation decreases with the increase of confining pressure. (5) The relationship between the effective permeability and the water saturation agrees with the power function relationship, namely, k_∞=k₀(1-S_w)^c.