Carbonate coreflood experiments have demonstrated the potential for Advanced Ion Management (AIMSM) to significantly increase oil recovery compared to waterflood using formation water. AIMSM involves adding and/or removing ions from the injection water to improve waterflood performance. AIMSM further improves current state-of-the-art processes through the addition of certain salts and/or the softening of water. Simulations have accurately matched the experiments, providing a tool to assess field-scale recovery and supporting the premise that the increased recovery is due to a change in wettability. This study shows that a relatively inexpensive and straightforward modification of injection water composition can significantly increase oil recovery.

Oil can be recovered from fractured, initially oil-wet carbonate reservoirs by wettability alteration with dilute surfactant and electrolyte solutions. The aim of this work is to study the effect of salinity, surfactant concentration, electrolyte concentration, and temperature on the wettability alteration and identify underlying mechanisms. Contact angles, phase behavior, and interfacial tensions were measured with two oils (a model oil and a field oil) at temperatures up to 90 • C. There exists an optimal surfactant concentration for varying salinity and an optimal salinity for varying surfactant concentration at which the wettability alteration on an oil-aged calcite plate is the maximum for anionic surfactants studied. As the salinity increases, the extent of maximum wettability alteration decreases; also the surfactant concentration needed for the maximum wettability alteration decreases. IFT and contact angle were found to have the same optimal salinity for a given concentration of anionic surfactants studied. As the ethoxylation increases in anionic surfactants, the extent of wettability alteration on calcite plates increases. Wettability of oil-aged calcite plates can be altered by divalent ions at a high temperature (90 • C and above). Sulfate ions alter wettability to a greater extent in the presence of magnesium and calcium ions than in the absence. A high concentration of calcium ions can alter wettability alone. Magnesium ions alone do not change calcite plate wettability. Wettability alteration increases the oil recovery rate from initially oil-wet Texas Cordova Cream limestone cores by imbibition.

Neutron reflectivity was used to characterize the structure of end-grafted deuterated poly-(dimethylsiloxane) (d-PDMS) brushes on SiO x wafers exposed to liquid and supercritical carbon dioxide (CO2). The solvent quality was tuned continuously over a large range from ideal gas conditions to a near-Θ solvent by varying temperature and CO2 density. Two distinct regions were seen in the segment density profile as a function of distance from the surface: (i) an inner concentrated region near the substrate where the segment density is high due to the strong attractive short-and long-ranged interactions between the d-PDMS and the SiO x substrate and the attractive intra-and interchain interactions and (ii) an outer solvated region that is dilute in polymer due to solvation by CO2. In the outer solvated region, the well-defined block profile at the worst solvent conditions changes to a more parabolic profile with improving solvent quality. The thickness and volume fraction profiles for the outer solvated region change much more with solvent quality than has been seen in previous studies with incompressible solvents, due to the high asymmetry in the intermolecular interactions as well as the large compressibility and free volume differences between the polymer segments and the solvent.

The influence of carbon dioxide (CO2) sorption on the phase behavior of two polystyrene-block-poly(n-alkyl methacrylate) copolymers was studied. One, polystyrene-block-poly(n-hexyl methacrylate), P(S-b-nHMA), exhibits an order−disorder transition (ODT), whereas the other, polystyrene-block-poly(n-butyl methacrylate), P(S-b-nBMA), exhibits a lower disorder−order transition (LDOT). CO2 sorption increases miscibility of the segments in P(S-b-nHMA) slightly:  the ODT is depressed by less than 7 °C at a CO2 fluid density of 0.25 g/cm3, which corresponds to 7 vol % dilation of the copolymer with CO2 at the conditions studied. In contrast, CO2 sorption decreased the miscibility of P(S-b-nBMA) markedly:  the LDOT was depressed by more than 70 °C at densities < 0.06 g/cm3, which corresponds to less than 3 vol % sorption of CO2. Unlike P(S-b-nHMA), ordering transitions in CO2-dilated P(S-b-nBMA) exhibit a pronounced thermal hysteresis that increases with increasing volume fraction of sorbed diluent. The hysteresis is a consequence of the sensitivity of the LDOT system to differences in CO2 sorption between the ordered and disordered states, as evidenced by neutron reflectivity measurements. The difference in the effect of CO2 sorption on the phase behavior of the copolymers is attributed to the different nature of the transitions. The entropically driven LDOT is depressed by differential dilation of the copolymer domains, which increases both the compressibility of the system and disparities in compressibility between the blocks. In contrast, the enthalpically driven ODT is depressed by the screening of segmental interactions by CO2 and is less sensitive to compressibility.

The self-diffusivities of high molecular weight polystyrene chains in CO 2-swollen polystyrene matrices were measured in real time using neutron reflectivity. Bilayer films of hydrogenated and deuterated polystyrene (PS) were prepared on silicon substrates and exposed to compressed CO2. The broadening of the interface between the films as a function of time was determined from the reflectivity profiles, yielding the chain diffusivity. Diffusivity was studied as a function of polymer molecular weight, concentration of CO2 in the polymer film, and temperature. Nearly an order of magnitude enhancement in the diffusivity of polystyrene chains (M ) 2 × 10 5 ), from 1.62 × 10 -16 to 9.35 × 10 -16 cm 2 /s, was found with a modest increase in the concentration of CO2 in the polystyrene (from 8.9 to 11.3 wt %) at 62 °C. This concentration dependence was modeled using the Vrentas-Duda free volume theory. [50][51][52] At a constant temperature and CO2 pressure the polystyrene diffusivity scaled as M -2.38 . The scaling of the self-diffusivity of PS in CO2-swollen PS with T -Tg, where Tg is the glass transition temperature depressed by the presence of the solvent, is discussed.