Flow Dynamics of Microemulsion-Forming Surfactants and its Implications for Enhanced Oil Recovery: A Microfluidic Study

The microfluidic experiments were conducted in this paper to clarify the flow dynamics of in situ microemulsion and further understand its EOR performances. Two kinds of 2.5D glass micromodel with varied depths of pore and throat are fabricated. One is designed for the imbibition tests, which consists of two fractures and a tight matrix. Another one is a fractured micromodel designed for the flooding tests. The micromodels are originally water wet, and can be altered to oil wet through the surface modification. At the same time, three microemulsion-forming surfactant solutions at the salinity of type I, II or III were prepared, respectively. Then the flow dynamics of these three surfactant solutions during imbibition and flooding process were visualized by the microfluidic experiments. Results show that the type I surfactant solution realizes the highest oil recovery rate in both water-wet and oil-wet imbibition micromodels. Meanwhile, the type III surfactant solution realize the highest oil recovery in both water-wet and oil-wet fractured micromodels.

Interaction of surfactants with barley leaf surfaces: time-dependent recovery of contact angles is due to foliar uptake of surfactants

Main conclusion Time-dependent contact angle measurements of pure water on barley leaf surfaces allow quantifying the kinetics of surfactant diffusion into the leaf. Abstract Barley leaf surfaces were sprayed with three different aqueous concentrations (0.1, 1.0 and 10%) of a monodisperse (tetraethylene glycol monododecyl ether) and a polydisperse alcohol ethoxylate (BrijL4). After 10 min, the surfactant solutions on the leaf surfaces were dry leading to surfactant coverages of 1, 10 and 63 µg cm−2, respectively. The highest surfactant coverage (63 µg cm−2) affected leaf physiology (photosynthesis and water loss) rapidly and irreversibly and leaves were dying within 2–6 h. These effects on leaf physiology did not occur with the lower surfactant coverages (1 and 10 µg cm−2). Directly after spraying of 0.1 and 1.0% surfactant solution and complete drying (10 min), leaf surfaces were fully wettable for pure water and contact angles were 0°. Within 60 min (0.1% surfactant) and 6 h (1.0% surfactant), leaf surfaces were non-wettable again and contact angles of pure water were identical to control leaves. Scanning electron microscopy investigations directly performed after surfactant spraying and drying indicated that leaf surface wax crystallites were partially or fully covered by surfactants. Wax platelets with unaltered microstructure were fully visible again within 2 to 6 h after treatment with 0.1% surfactant solutions. Gas chromatographic analysis showed that surfactant amounts on leaf surfaces continuously disappeared over time. Our results indicate that surfactants, applied at realistic coverages between 1 and 10 µg cm−2 to barley leaf surfaces, leading to total wetting (contact angles of 0°) of leaf surfaces, are rapidly taken up by the leaves. As a consequence, leaf surface non-wettability is fully reappearing. An irreversible damage of the leaf surface fine structure leading to enhanced wetting and increased foliar transpiration seems highly unlikely at low surfactant coverages of 1 µg cm−2.

A microfluidic study of oil displacement in porous media at elevated temperature and pressure

Microfluidics methods offer possibilities for visual observations of oil recovery processes. Good control over test parameters also provides the opportunity to conduct tests that simulate representative reservoir conditions. This paper presents a setup and procedure development for microfluidic oil recovery tests at elevated temperature and pressure. Oil recovery factors and displacement patterns were determined in single- or two-step recovery tests using two crude oils, high salinity salt solutions and low salinity surfactant solutions. Neither the displacement pattern nor the recovery factor was significantly affected by the pressure range tested here. Increasing temperature affected the recovery factor significantly, but with opposite trends for the two tested crude oils. The difference was justified by changes in wettability alteration, due to variations in the amounts and structure of the acidic and basic oil fractions. Low salinity surfactant solutions enhanced the oil recovery for both oils.

Design of Laboratory Studies to Develop the Chemical Formulation for Surfactant-Polymer Flooding

Nowadays, chemical EOR methods are becoming more and more relevant, among which the alkali-surfactant-polymer flooding is of particular interest. The efficiency of this technology largely depends on the correct choice of the components of chemical formulation, which should be based on a set of laboratory experiments carried out in a given sequence. This paper presents a methodological approach to laboratory studies in order to develop an optimal surfactant-polymer formulation, taking into account the geological and physical characteristics of the target field and the properties of reservoir fluids. The experimental part of the research work was carried out in several stages, involving the analysis of the physicochemical characteristics of reservoir oil, the screening studies of surfactant and polymer samples, as well as a series of coreflood tests with a selected chemical formulation on the terrigenous reservoir models. During screening studies, the solubility and compatibility of the chemical components, the phase behavior of surfactant solutions with oil at different salinity values and water-oil ratios, static adsorption of chemicals on the rock and their thermal stability at reservoir temperature were investigated. Optimization of the chemical formulation was based on the results of IFT measurements of the surfactant solutions and rheological studies of the polymer solutions. At the stage of coreflood tests, physical simulation of the surfactant-polymer flooding was carried out on reservoir models using natural core material in order to optimize the composition and slug size of the developed chemical formulation. The obtained results of the displacement experiment were matched by numerical 1D simulation. Based on the results of the studies performed, an effective surfactant-polymer formulation has been designed, which provides the ultra-low IFT (2.8·10−4 mN/m) values and the ability to form stable middle-phase microemulsions when interacting with oil. The findings of thermal stability and static adsorption experiments confirmed a feasibility of selected chemicals for practical application. Within the framework of the study, the key technical parameters of proposed formulation were determined, which are required for up-scaled simulation study of the chemical flooding process at pilot site.