Swelling and embedment induced by sub- and super-critical-CO2 on the permeability of propped fractures in shale

Abstract

Swelling and embedment exert significant influence on the evolution of permeability in propped fractures, potentially consuming half the original gain in permeability. We measure the evolution of permeability in propped fractures of shale to both adsorbing CO2 and non-adsorbing He – accommodating the impacts of aperture change due to proppant pack compaction, particle deformation, and reversible and irreversible embedment. A typical linear relation is obtained in He cases as well as U-shaped curve for gaseous CO2 and W-shaped curve for supercritical CO2, which are proven to be dominated by the effective aperture and particle interval. An exception is discovered for liquid CO2, where the high injection pressure contributes as much as the swelling does and results in a linear curve with the lowest permeability. Concretely, approximately 50 ~ 70 % of the permeability recovers from the recovery of swelling after the desorption of CO2. The swelling, by itself, contributes 5 to 35 % of the total aperture reduction according to the adsorped mass. It also aggravates the embedment by 1.3 to 1.7 times before and after an injection of CO2. A new calibration equation of swelling and induced embedment has been generated by bringing in the Langmuir isothermal equation and verified with former experiments with different rock and sorbing gas types. Stability and accuracy of the predictions demonstrate the universality of the new method that will benefit both enhanced gas recovery and CO2 segregation