Gas release from
organic-rich shale rock plays a significant role
in the migration and production of hydrocarbons in the shale reservoir.
Despite recent progress in gas adsorption/desorption experiments and
molecular simulation, information on the actual gas release process
remains stagnated. Here, we demonstrate the real-time canister monitoring
technique as a powerful tool to investigate the kinetics of shale
gas release from freshly drilled core samples. Combined with the adsorption
capacity measurement, it is found that the gas released from the core
in the canister is the gas that was in the adsorbed state in the reservoir,
and the free gas and a fraction of adsorbed gas were already lost
during coring. Then, the reaction-based pseudo-first-order and pseudo-second-order
models and the diffusion-based double-exponential (DE) model are used
to interpret the kinetics of shale gas release. Instead of the coefficient
of determination (R
2), the corrected Akaike
information criterion technique (AICc) was used to determine
the best fitting model. It is found that the DE model best described
the kinetics of shale gas release from the core, and the success of
the DE model suggests that the shale gas release from the core is
a process of first-order, two-stage, and micropore diffusion-controlled.
Further, to investigate the dependence of gas release kinetics, the
half-life time (t
1/2) was calculated and
correlated with the adsorption capacity, gas concentrations, and total
organic matter (TOC) content. It is shown that increasing the gas
adsorption capacity, gas concentrations, and TOC content could accelerate
the rate of shale gas release. In addition, the potential implications
and an upscaling attempt of the release kinetics in evaluating the
shale gas content and production are also discussed. We found that
the slow stage of gas release controls the estimated ultimate recovery
(EUR) of shale gas wells, while the estimation based on the fast stage
would significantly lower the EUR. Overall, by using the real-time
wellsite canister monitoring technique, this study provides a unique
perspective for understanding the kinetics of gas release from tight
shale rock, as well as the long-term shale gas production behavior.