Large
amounts of fracturing fluid retained in a shale reservoir
could not only restrict gas production through aqueous phase trapping
(APT) but also cause potential contamination of groundwater. In this
work, experiments modeling in situ aqueous imbibition and flowback
were conducted to quantitatively investigate the APT behavior in shales,
including matrix, natural fracture, and artificial fracture. Results
show that the forward imbibition process is slower than the reverse
imbibition process. The aqueous phase tends to be imbibed through
parallel bedding. Permeability reduction rates of matrix, natural
fracture, and artificial fracture cores after imbibition could reach
100, 85, and 70%, respectively. Meanwhile, it is demonstrated that
the aqueous flowback efficiency depends upon flowback timing, pressure
difference, initial permeability, and bedding direction. The flowback
efficiencies of matrix, natural fracture, and artificial fracture
cores could be less than 7%, less than 30%, and less than 15%, respectively.
Additionally, the permeability recovery rates of those could be less
than 19%, less than 39%, and less than 67%, respectively. Finally,
shale APT mechanisms are analyzed from both geological and engineering
aspects. The quantitative investigation of shale APT is conducive
to economically and environmentally developing shale gas reservoirs.