(132g) Interfacial Tensions of System Comprising Nitrogen, Aqueous Potassium Iodide, Decane and Iododecane at Elevated Pressures and Temperatures

The interfacial tensions between reservoir fluids play an important role in both enhanced oil recovery (EOR) and carbon geological storage (CGS) [1, 2]. In core flooding experiments, analogue fluids such as N₂, decane and simple brines are often used to represent gas, oil and aqueous phases. To enhance the contrast between fluids in X-ray CT imaging, oil and aqueous phases are commonly doped with iododecane and iodide-containing salts, respectively [3]. The effect of these iodide-doped fluids on the interfacial tension is studied in this work.

The pendant drop method was used to measure the interfacial tension of the system comprising N₂, 7wt% KI (aq), decane and iododecane mixture at various temperatures and pressures. A thermostatic high-pressure view cell was firstly filled with the lighter fluid. The denser fluid was then injected though a capillary into the cell to form a drop suspended at the tip of the capillary. The profile of the drop was captured by a CCD camera and analyzed by the Axisymmetric Drop Shape Analysis (ADSA) method [4]. The densities of the coexisting fluids were either measured using a two phase densimeter at each state point or calculated from suitable models. The interfacial tension between the two fluids was then calculated by iterative fitting of the Young-Laplace equation [5].

It should be noted that the experimental result for interfacial tension depends upon the calibration of the CCD (in terms of pixels per unit length). The captured image may be enlarged or shrunk if the refractive index of the bulk phase inside the view cell is different from that during the calibration. Therefore, we have developed an optical model to quantify the effect of refractive index changes on the measured interfacial tension. This model was used to apply corrections for the effect of refractive index changes.

In this work, we report the interfacial tensions between N₂, 7wt% KI (aq), and decane-iododecane mixtures with iododecane mass fraction of 0, 50%, 70%, 90% and 100%, at temperatures from 298 K to 353 K and at pressures from 1 MPa to 30 MPa. The expanded relative uncertainty at 95% confidence is about 1%. Interfacial tensions between N₂ and the aqueous/oil phases are both observed to decrease with increase of either pressure or temperature. The interfacial tension between aqueous phase and decane-iododecane mixtures decreases with the increasing temperature and vary little with pressure. In the N₂-KI (aq) system, the interfacial tension increases as salinity increases and, for 7wt% KI (aq), is about 2.5 mN/m greater than that in the salt-free system over the entire temperature and pressure ranges. In the N₂ + decane-iododecane mixture system, the interfacial tension increases with increase of the iododecane mass fraction, while in the KI (aq) + decane-iododecane mixture system, the interfacial tension decreases with the mass fraction of iododecane. Empirical equations were developed to correlate all of the measured data in terms of temperature, pressure, KI molality and iododecane mass fraction.

This study investigates the effect of introducing iodide-doped material on the interfacial tension of N₂, KI (aq) and decane-iododecane mixtures. The interfacial tension data obtained can support and assist the interpretation of multiphase flow and wetting behaviour in porous media and provide fundamental information for more reliable numerical reservoir simulation.

References

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2. Michael, K., et al., Geological storage of CO2 in saline aquifers—A review of the experience from existing storage operations. International Journal of Greenhouse Gas Control, 2010. 4(4): p. 659-667.
3. Vinegar, H.J. and S.L. Wellington, Tomographic imaging of three‐phase flow experiments. Review of Scientific Instruments, 1987. 58(1): p. 96-107.
4. Cheng, P., et al., Automation of axisymmetric drop shape analysis for measurements of interfacial tensions and contact angles. Colloids and Surfaces, 1990. 43(2): p. 151-167.
5. Young, T., III. An essay on the cohesion of fluids. Philosophical Transactions of the Royal Society of London, 1805. 95: p. 65-87.