Experiment on stress sensitivity of coal permeability at different scales in Baode and Hancheng areas

Key words:  permeability  effecive stress  scale effect  stress sensibility  fracture volume compressibility

Abstract:

The coal samples from Baode and Hancheng areas in the eastern margin of Ordos Basin were selected, and the stress sensitivity experiments under different stress conditions were carried out. Then, the influences of coal rock scale on the stress sensitivity of coal were discussed. The experimental results show that the stress sensitivity of small-scale coal sample is more significant than that of large-scale coal sample, and the permeability changes much more. After a rise and fall of the effective stress, the permeability of the coal sample is lost to some extent, and the permeability recovery rate of the small-scale coal sample is lower than that of the large-scale coal sample. At the same time of effective stress change rate, the volume deformation of small-scale coal sample is larger than that of large-scale coal sample, and its compression coefficient is much higher than the latter. Furthermore, it is found that the scale effect is more significant in the middle and low rank coal reservoirs than in the middle and high rank coal reservoirs. It is also found that the primary structural coal is developed in Baode. The sensitivity of coal seam stress is weak during the development process, and the effect of coalbed methane production is good. The mylonite is developed in Hancheng. The sensitivity of coal seam permeability is enhanced during the development process, and the effect of coalbed methane production is low. Compared with the scale of coal sample, the influence of coal rank on the stress sensitivity of coal sample is much less.