Surface Tension, Interfacial Tension and Phase Behavior: Interactions of Surfactant/Polymer Solutions with Crude Oil

Advanced oil recovery techniques, beyond primary and secondary recovery, are required in order to produce additional oil in existing reservoir rock. Here, we evaluated a combination of polymer and surfactant aqueous solutions, in order to generate a working fluid capable of achieving high-performance enhanced oil recovery (EOR). In this recovery process, surfactant is added to the water flooding mixture in order to lower the interfacial tension between the oil and the water. If the interfacial tension can be decreased by ~1,000-fold, then the aqueous solution can mobilize and displace the oil. Moreover, a polymer is added to the aqueous solution in order to increase the viscosity of the working fluid. Aqueous solutions with a viscosity higher than the oil viscosity can produce a stable flow of oil. However, the exact combination and concentration needed for these two key components to be effective is dependent on each oil reservoir and requires several experiments and specific tuning in order to yield an effective design. In order to determine the optimal combination, the effects of the average molecular weight of the polymers, the surfactant chemistry, and their combinations in salt solutions (at varying salt concentrations) were investigated. Specifically, the surface tension of aqueous solutions against air and the interfacial tension against oil and the phase behavior of the polymer-surfactant systems were evaluated with a model hydrocarbon, dodecane, and with crude oil. By varying the molecular properties of the surfactant and the polymer, we found a technically promising surfactant-polymer combination for potential EOR application

Interfacial Tension and Phase Behavior of Oil/Aqueous Systems with Applications to Enhanced Oil Recovery

Chemical enhanced oil recovery (cEOR) aims to increase the oil recovery of mature oil fields, using aqueous solutions of surfactants and polymers, to mobilize trapped oil and maintain production. The interfacial tensions (IFTs) between the injected aqueous solution, the oil droplets in reservoirs, and other possible phases formed (e.g., a “middle phase” microemulsion) are important for designing and assessing a chemical formulation. Ultralow IFTs, less than 10-2 mN·m1, are needed to increase the capillary number and help mobilize trapped oil droplets. Despite this fact, phase behavior tests have received more attention than IFTs for designing and evaluating surfactant formulations that result in high oil recovery efficiencies, because incorporating reliable IFTs into such evaluation process is avoided due to difficulties in obtaining reliable values. Hence, the main thrusts of this dissertation are to: (a) develop robust IFT measurement protocols for obtaining reliable IFTs regardless of the complexity of water and oil phase constituents and (b) improve the existing surfactant polymer formulation evaluation and screening processes by successfully incorporating the IFT as one of the critical parameters. First, two robust tensiometry protocols using the known emerging bubble method (EBM) and the spinning bubble method (SBM) were demonstrated, for determining accurately equilibrium surface tensions (ESTs) and equilibrium IFTs (EIFTs). The protocols are used for measuring the dynamic surface tensions (DSTs), determining the steady state values, and establishing the stability of the steady state values by applying small surface area perturbations by monitoring the ST or IFT relaxation behavior. The perturbations were applied by abruptly expanding or compressing surface areas by changing the bubble sizes with an automated dispenser for the EBM, and by altering the rotation frequency of the spinning tube for the SBM. Such robust tension measurement protocols were applied for Triton X-100 aqueous solutions at a fixed concentration above its critical micelle concentration (CMC). The EST value of the model solution was 31.5 ± 0.1 mN·m-1 with the EBM and 30.8 ± 0.2 mN·m-1with the SBM. These protocols provide robust criteria for establishing the EST values. Second, the EIFTs of a commercial single chain anionic surfactant solution in a synthetic brine against a crude oil from an active reservoir were determined with the new protocol described earlier. The commercial surfactant used here has an oligopropoxy group between a hydrophobic chain and a sulfate head group. The synthetic brine has 9,700 ppm of total dissolved salts, which are a mixture of sodium chloride (NaCl), potassium chloride (KCl), manganese (II) chloride tetrahydrate (MnCl2·4H2O), magnesium (II) chloride hexahydrate (MgCl2·6H2O), barium chloride dihydrate (BaCl2·2H2O), sodium sulfate decahydrate (Na2SO4·10H2O), sodium bicarbonate (NaHCO3), and calcium chloride dihydrate (CaCl2·2H2O). The DSTs curves of the surfactant concentrations from 0.1 ppm to 10,000 ppm by weight had a simple adsorption/desorption equilibrium at air/water surface with surfactant diffusion from bulk aqueous phase. Such a mechanism was also observed from the tension relaxation behavior after area perturbations for the oil/water interfaces while DIFT measurements. The CMC of the commercial surfactant was determined to be 12 ppm in water and 1 ppm in the synthetic brine used

Adsorption and Diffusion of Small Alcohols in Zeolitic Imidazolate Frameworks ZIF‑8 and ZIF-90

We examine the adsorption and diffusion of small alcohols in ZIF-8 and ZIF-90 with a combined experimental and modeling approach. Our Grand Canonical Monte Carlo (GCMC) simulations predict that both ZIFs exhibit a slight adsorption selectivity for ethanol over methanol, in good agreement with previous experimental data. The adsorption uptake of the alcohols at low pressures is found to be significantly higher in ZIF-90 than ZIF-8. Our simulations indicate that this is due to hydrogen bonding between the alcohols and the carbonyl group of ZIF-90 but that this effect is not strong enough to cause appreciable flexibility of the ZIF-90 framework during adsorption. We also report alcohol self-diffusivities and Arrhenius parameters measured using pulsed field gradient NMR (PFG-NMR) and molecular dynamics (MD) simulations. The diffusivities measured using PFG-NMR indicate that the diffusion selectivity of methanol over ethanol is significantly higher in ZIF-8 (<i>S</i> = 229) than in ZIF-90 (<i>S</i> = 6) at <i>T</i> = 25 °C. Qualitative agreement is obtained between experimental and simulated diffusivities using the generalized AMBER (GAFF) force field including framework flexibility