Experimental observations of matrix swelling area propagation on permeability evolution using natural and reconstituted samples

Authors

Qingquan Liu, China University of Mining and Technology, University of WollongongFollow
Yuanping Cheng, University of Wollongong, China University of Mining and TechnologyFollow
Ting X. Ren, University of WollongongFollow
Hongwen Jing, China University of Mining and Technology
Qingyi Tu, China University of Mining Technology
Jun Dong, China University of Mining and Technology

RIS ID

114337

Publication Details

Liu, Q., Cheng, Y., Ren, T., Jing, H., Tu, Q. & Dong, J. (2016). Experimental observations of matrix swelling area propagation on permeability evolution using natural and reconstituted samples. Journal of Natural Gas Science and Engineering, 34 680-688.

Abstract

Many researchers have concluded that the permeability should be measured after the adsorption equilibrium state is reached and in many permeability models, it is normally assumed that p_^m (pressure in the coal matrix) is equalized with p_f (pressure in the fractures). However, when the dynamic balance between p_m and p_f is broken which exists in most coalbed methane engineering, the differences between the two pressures induced by gas diffusion and matrix shape factor will generate nonuniform matrix swelling which have not been well learned to date, thus influence the permeability evolution. It is of great importance to investigate this issue on account of it will play a more important role in CO₂-enhanced coalbed methane and CO₂ sequestration engineering as the coal adsorption capacity for CO₂ is considerably higher than that for CH₄. To achieve this target, a series of novel coal permeability tests and simultaneous strain measurements were conducted using both natural coal and reconstituted coal. In these experiments, the radial strain evolution characteristics and the permeability evolution characteristics as a function of the adsorption equilibrium time and confining pressure were obtained. Based on the experimental results, the effects of the differences between p_m and p_f on radial strain evolution and coal permeability evolution were discussed, and a new matrix swelling area propagation theory was achieved. In addition, the differences between natural coal and reconstituted coal in terms of their matrix swelling and stress sensitivity properties were obtained.