Sorption Hysteresis of Hardened Cement Pastes

Mesopores in porous solids can produce a pronounced sorption hysteresis at moderate and high reduced vapor pressures of the ambient gas that is condensed in the pores. Unlike to other conventional porous materials, cement pastes often behave exceptionally. The water sorption hysteresis frequently persists at very low humidity. This hysteresis is reflected in a corresponding hysteresis loop of the solid skeleton volume. We discuss a theoretical model based on the strong compression force exerted by a condensate on the walls of narrow slit pores embedded in an elastic solid. This compression force is shown to be capable of shifting walls of narrow slit pores. Humidity-dependent closing and reopening of slit pores can produce hysteresis loops even at low humidity.

Experimental study on the adverse effect of gel fracturing fluid on gas sorption behavior for Illinois coal

Hydraulic fracturing is an effective technology for coal reservoir stimulation.After fracturing operation and flowback,a fraction of fracturing fluid will be essentially remained in the formation which ultimately damages the flowability of the formation.In this study,we quantified the gel-based fracturing fluid induced damages on gas sorption for Illinois coal in US.We conducted the high-pressure methane and CO_(2)sorption experiments to investigate the sorption damage due to the gel residue.The infrared spectroscopy tests were used to analyze the evolution of the functional group of the coal during fracturing fluid treatment.The results show that there is no significant chemical reaction between the fracturing fluid and coal,and the damage of sorption is attributed to the physical blockage and interactions.As the concentration of fracturing fluid increases,the density of residues on the coal surface increases and the adhesion film becomes progressively denser.The adhesion film on coal can apparently reduce the number of adsorption sites for gas and lead to a decrease of gas sorption capacity.In addition,the gel residue can decrease the interconnectivity of pore structure of coal which can also limit the sorption capacity by isolating the gas from the potential sorption sites.For the low concentration of fracturing fluid,the Langmuir volume was reduced to less than one-half of that of raw coal.After the fracturing fluid invades,the desorption hysteresis of methane and CO_(2)in coal was found to be amplified.The impact on the methane desorption hysteresis is significantly higher than CO_(2)does.The reason for the increasing of hysteresis may be that the adsorption swelling caused by the residue adhered on the pore edge,or the pore blockage caused by the residue invasion under high gas pressure.The results of this study quantitatively confirm the fracturing fluid induced gas sorption damage on coal and provide a baseline assessment for coal fracturing fluid formulation and technology.