Experimental investigation of phase behavior in porous media
The influence of porous media in the phase behaviour of reservoir fluids may affect well performance and ultimate recovery. Reservoir fluids in tight formations are subjected to a high degree of confinement which influences the phase behaviour, i.e. confined fluids show different phase behaviour than bulk fluids. Under these conditions, van der Waals forces and fluid structural changes play a significant role, together with selective adsorption and large capillary pressure, which shifts the saturation pressure of confined fluids.
Knowledge of the phase behaviour of the reservoir fluids under confinement is limited and mainly theoretical. Confined fluids cannot be studied through conventional PVT but it is possible to determine their boiling points through differential scanning calorimetry, as previously reported by Luo et al.1 and Cho et al.2. However, there is still scarcity of these type of experimental data, which are needed to quantify the magnitude of this phenomenon and to validate theoretical models used in production forecast.
The phase behaviour of three n-alkanes (n-hexane, n-octane and n-decane) was determined up to 30 bar through a differential heat flux calorimeter. The bulk fluid was studied together with the fluid confined in two different silica nanoporous materials. Reservoir chalk from the North Sea was also used as porous material.
Isobaric thermograms of n-octane and n-decane in 5 and 13 nm porous media showed two peaks, the lower one corresponding to bulk fluid and the higher to the confined fluid, which indicates that the saturation temperature of the bulk fluid is lower than that of the confined fluid. The peak separation increased with the decrease in the pore diameter. The shift observed in the vaporization temperature is in agreement with previous results by Luo et al.1
1 44, 11506-11513, 2016
Cho et al., Chem. Eng. Sci. 177, 481-490, 2018