An experimental technique is developed to measure the interfacial tensions of the crude oil + reservoir brine + CO2 systems at pressures from (0.1 to 31.4) MPa and two temperatures (27 and 58) °C using the axisymmetric drop shape analysis (ADSA) technique for the pendant drop case. The measured dynamic interfacial tension is gradually reduced to an equilibrium value. For both the reservoir brine + CO2 system and the crude oil + CO2 system, the equilibrium interfacial tension decreases as the pressure increases, whereas it increases as the temperature increases. For the reservoir brine + CO2 system, the interfacial tension data are not available at P ≥ 12.238 MPa and 58 °C because the pendant brine drop cannot be formed in the CO2 phase. However, for the crude oil + CO2 system, the equilibrium interfacial tension remains almost constant at P ≥ 8.879 MPa and 27 °C or at P ≥ 13.362 MPa and 58 °C. Under the same conditions, nevertheless, the equilibrium interfacial tension of the crude oil + reservoir brine +...

Interfacial Tensions of the Crude Oil + Reservoir Brine + CO2 Systems at Pressures up to 31 MPa and Temperatures of 27 °C and 58 °C

An experimental method has been developed to determine the wettability, i.e., the contact angle, of a reservoir brine−reservoir rock system with dissolution of CO2 at high pressures and elevated temperatures by using the axisymmetric drop shape analysis (ADSA) technique for the sessile drop case. Prior to the experiment, a rock slide is horizontally placed in a specially designed rock slide holder in a see-through windowed high-pressure cell, which is subsequently filled with CO2 at a prespecified pressure and a constant temperature. Then, a reservoir brine sample is introduced by using a syringe delivery system to form a sessile brine drop on the rock slide inside the pressure cell. The sequential digital images of the dynamic sessile brine drop are acquired and analyzed by applying computer-aided image acquisition and processing techniques to measure the dynamic contact angles at different times. It is found that the dynamic contact angle between the reservoir brine and the reservoir rock remains almost...

Wettability Determination of the Reservoir Brine−Reservoir Rock System with Dissolution of CO2 at High Pressures and Elevated Temperatures

A critical look at reactions in class I and II gas-expanded liquids using CO2 and other gases

Concern over global warming has increased interest in quantification of the dissolution of CO2 in (sub-)- surface water. The mechanisms of the mass transfer of CO2 in aquifers and of transfer to surface water have many common features. The advantage of experiments using bulk water is that the underlying assumptions to the quantify mass-transfer rate can be validated. Dissolution of CO2 into water (or oil) increases the density of the liquid phase. This density change destabilizes the interface and enhances the transfer rate across the interface by natural convection. This paper describes a series of experiments performed in a cylindrical PVT- cell at a pressure range of pi ) 10-50 bar, where a fixed volume of CO2 gas was brought into contact with a column of distilled water. The transfer rate is inferred by following the gas pressure history. The results show that the mass-transfer rate across the interface is much faster than that predicted by Fickian diffusion and increases with increasing initial gas pressure. The theoretical interpretation of the observed effects is based on diffusion and natural convection phenomena. The CO2 concentration at the interface is estimated from the gas pressure using Henry's solubility law, in which the coefficient varies with both pressure and temperature. Good agreement between the experiments and the theoretical results has been obtained. tion of CO2 in the atmosphere, geological storage of CO2 is considered. 2-4 When CO2 is injected into an aquifer, the competition between viscous, capillary, and buoyancy forces determines the flow pattern. Eventually, due to buoyancy forces CO2 will migrate upward and be trapped under the cap rock due to capillary forces. In this case an interface between a CO2- rich phase and brine exists. Subsequently, CO2 starts to dissolve into water by molecular diffusion when it is in contact with the brine. The dissolution of CO2 increases the density of brine. 5 This density increase together with temperature fluctuations in the aquifer (which may be only partially compensated by pressure gradients 6 ) destabilize the CO2-brine interface and accelerate the transfer rate of CO2 into the brine by natural convection. 5-10 The occurrence of natural convection signifi- cantly increases the total storage rate in the aquifer since convection currents bring the fresh brine to the top. Hence, the quantification of CO2 dissolution in water and understanding the transport mechanisms are crucial in predicting the potential and long-term behavior of CO2 in aquifers. Unfortunately there are only a few experimental data in the literature, involving mass transfer between water and CO2 under elevated pressures. Weir et al. 11 were the first to point out the importance of natural convection for sequestration of CO2. Yang and Gu 8 performed experiments in bulk where a column of CO2 at high pressure was in contact with water. The procedure was similar to the established approach in which the changes in gas pressure relate the gas to the transfer rate. 12-15 A modified diffusion equation with an effective diffusivity was used to describe the mass-transfer process of CO2 into the brine. Good agreement between the experiments and the model was observed by choosing effective diffusion coefficients 2 orders of mag- nitude larger than the molecular diffusivity of CO2 into water. However, the authors pointed out that the accurate modeling of the experiments should consider natural convection effects. Farajzadeh et al. 9,10 reported experimental results for the same system, in a slightly different geometry, showing initially enhanced mass transfer followed by a classical diffusion behavior in long times. A physical model based on Fick's second law and Henry's law was used to interpret the experimental data. It was found that the mass-transfer process cannot be modeled with a modified Fick's second law with a single effective diffusion coefficient for the CO2-water system at high pressures. Nevertheless, the initial stages and later stages of the experiments can be modeled individually with the described model. Arendt et al. 16 applied a Schlieren method and a three- mode magnetic suspension balance connected to an optical cell to analyze the mass transfer of the CO2-water system up to 360 bar. Good agreement between their model (linear superposi- tion of free conVection and Marangoni convection) and the experiment was obtained. The addition of surfactant suppressed the Marangoni convection in their experiments, while in the experiments of ref 9, addition of surfactant did not have a significant effect on the transfer rate of CO2. A similar mass- transfer enhancement was observed for the mass transfer between a gaseous CO2-rich phase with two hydrocarbons (n- decane and n-hexadecane) 9,10 due to the fact that CO2 increases the hydrocarbon density. 17 The effect becomes less significant with increasing oil viscosity. This has implications for oil recovery. Indeed in geological storage of CO2 the early time behavior is governed by diffusion before the onset of the natural

Enhanced Mass Transfer of CO2 into Water: Experiment and Modeling

The success of CO2 storage in deep saline aquifers and depleted oil and gas reservoirs is largely controlled by interfacial phenomena among fluid phases and rock pore spaces. Particularly, the wettability of the rock matrix has a strong effect on capillary pressure, relative permeability, and the distribution of phases within the pore space and thus on the entire displacement mechanism and storage capacity. Precise understanding of wettability behavior is therefore fundamental when injecting CO2 into geological formations to sequestrate CO2 and/or to enhance gas/oil production. In this study, the contact angles of Bentheimer sandstone/water/CO2 or flue gas have been evaluated experimentally using the captive-bubble technique in the pressure range from 0.2 to 15 MPa. The experiments were conducted using different compositions of aqueous phase with respect to CO2, i.e., unsaturated and fully saturated. It has been shown that a reliable contact-angle determination needs to be conducted using a pre-equilibrat...

B Arendt

Papers

Interaction of interfacial convection and mass transfer effects in the system CO2–water