The reservoir permeability dominates the transport of gas and water in coal seam. However, coal seams rich in gas usually contain various pores and fractures blocked by a large amount of minerals, which leads to an ultra-low permeability and gas extraction rate, and thus an increase of drilling workload. We first propose a thermo-hydro-mechanical-chemical coupled model (THMC) for the acid fracturing enhanced coalbed methane recovery (AF-ECBM). Then, this model is applied to simulate the variation of key parameters during AF-ECBM using a 2D geometry. The effect of different extraction schedules are comparatively analyzed to give an insight into these complex coupling responses in coal seam. Result confirms that the AF-ECBM is an effective way to increase the reservoir permeability and improve the gas production using the proposed model. The range of permeability increment zone increases most dramatically in the way of acid fracturing, followed by none-acid fracturing and acidizing over time. The gas production in order is: acid fracturing (AF-ECBM) > fracturing (F-ECBM) > acidification (A-ECBM)> direct extraction (D-CBM).

The problem of slope vibration induced by flood discharge of high dams cannot be ignored. In this paper, this problem is simplified to be the relationship among the fluctuating pressures, the inherent properties of the slope system, and its dynamic responses. The characteristics of fluctuating pressures in the plunge pool during flood discharge are analyzed by the hydraulic model test. And a numerical slope model consisting of the finite element domain and the PML domain is established to study the inherent characteristics and vibration responses by numerical simulation. The results show that the flow fluctuation in plunge pool is a continuous and stable random vibration process. And the fluctuating pressures on the bottom area of the plunge pool are greater than that of the sidewall, but the fluctuation phenomenon at the sidewall is more intense. In addition, the slope displacement vibration intensity caused by fluctuating pressures is small, only at the micron level. The fluctuating pressures on the bottom area of the plunge pool are the dominant factor affecting the kinetic energy density distribution of the slope. This work provides a simple and efficient method for the study of slope vibration induced by high dam flood discharge.