A convenient and practical triaxial coupled seepage testing apparatus for deep buried coal.

As the world's shallow coal resources are being depleted, resource development continues to progress faster. To explore the coupled hydromechanical behavior of coal reserves that are buried deep underground under high stress, complex seepage, high temperature, adsorption, and desorption, we have developed a triaxial seepage testing apparatus under multifactor coupling effect. The system consists of a high-pressure and high-precision servo control loading system, a triaxial core holder (TEMCO), a seepage dynamic control system, a low-field Nuclear Magnetic Resonance (NMR) test system, a constant temperature control system, and a data acquisition and monitoring system. This system is capable of applying high pressure and long-term loading for specimens under adsorption or desorption. In addition, both steady-state method and pressure transient methods can be applied, thus covering the entire range for coal reserves buried deep from ultralow permeability to high permeability and significantly shortening the testing time. The characteristics of pores and fractures in the specimens and their impacts on permeability can be quantitatively evaluated by the low-field NMR experimental technique. We conducted experiments to understand the evolution of permeability of different gases under different stress conditions and to study the impact of adsorption on pore size distribution. Our experimental results show that the performance of this system is stable and reliable, which allow it to reflect the coupled hydromechanical response of coal buried deep underground. We envision this apparatus has a wide range of application value and can provide a scientific experimental basis for improving the recovery of coalbed methane and geological sequestration of CO2 in the future.