Development and application of triaxial seepage test system for gas-water two-phase in coal rock

The research of gas-water two-phase flow is significant for gas extraction and CBM in deep coal rock, so a triaxial seepage test system for gas-water two-phase in coal rock is independently developed. The device is equipped has various stress loading modes such as constant pressure, gradient, waveform loading, and manual mode, which can realize the study of the gas phase, water phase, and gas-water two-phase seepage law in coal rock under cyclic loading and unloading. The results of seepage experiments showed that the two-phase seepage test required injection of “gas-driven water” to realize the mixed gas-water seepage, and the appearance of significant seepage in the water phase was about 6100 s earlier than that of single-phase seepage. Compared with single-phase seepage, the damage of the specimens after two-phase seepage tests was more remarkable, the number of cracks and crack area of the specimen were the highest, and the strain hysteresis loops were more obvious. Under the condition of incomplete pressure relief, the permeability of gas in coal rock showed a trend of increasing and then decreasing during two-phase seepage due to the influence of the water phase, and the value was lower than 0.0025 mD. •Triaxial seepage test system for gas-water two-phase in coal rock is developed.•Axial pressure and confining pressure are loaded and unloaded at the same time.•The stress path is designed in a combination of large and small cycles.•Realizing gas-water two-phase mixed seepage in the way of “gas drive water".