On the transport of emulsions in porous media

Study of the oil geopermeation patterns: A case study of ANSYS CFX software application for computer modeling

Mathematical simulation of oil permeation through the porous media is the crucial topical problem in the framework of localization and liquidation of emergency oil spills. The main objective of this study was to establish the oil contamination level and oil contamination depth for different soil types which is of particular relevance from the standpoint of environmental safety. Four types of soils were taken for investigation as follows Cambisol with sand texture (No. 1), Luvisol (gray forest), with loamy sand texture (No. 2), Black Typical Chernozem with sandy loam texture (No. 3), Kastanozem (pine forest terrace under the pines) with sand texture (No. 4). The task of predicting the temporal-spatial indicators of oil permeation in the soil during accidental spills was solved using ANSYS CFX software allowing to simulate the absorption amount of oil into the ground. Visualization of oil concentration and velocity for studied soil samples was carried out. Determination of petroleum hydrocarbons concentration by the gravimetric method indicated a direct correlation between oil content in the soil and the porosity of the investigated soil samples. In order to determine the rate of hydrocarbon permeation through the dry and wet soil layer comparative experiments were carried out for the following systems: oil - dry soil and oil - wet soil. Permeation coefficients for dry samples from No. 1 to No. 4 were set at the rate 0.0073 m ∙ day^-1, 0.0077 m ∙ day^-1, 0.0083 m ∙ day^-1, 0.0067 m ∙ day^-1 respectively, and for wet soils 0.0083 m ∙ day^-1, 0.0093 m ∙ day^-1, 0.0093 m ∙ day^-1, 0.0083 m ∙ day^-1 consequently. The obtained hydrocarbon permeation coefficients for different systems allow calculating the depth of oil penetration for a given time after the spill, taking into account soil moisture. The dependence of oil concentration and permeation rate distribution through the soil fully reflects reliability of the experimental data, thereby confirming the verification of the adequacy of the computer model based on the ANSYS CFX software.

Chemical Migration and Emulsification of Surfactant-Polymer Flooding

With a long sand-packed core with multiple sample points, a laboratory surfactant-polymer flooding experiment was performed to study the emulsification mechanism, chemical migration mechanism, and the chromatographic separation of surfactant-polymer flooding system. After water flooding, the surfactant-polymer flooding with an emulsified system enhances oil recovery by 17.88%. The water cut of produced fluid began to decrease at the injection of 0.4 pore volume (PV) surfactant-polymer slug and got the minimum at 1.2 PV. During the surfactant-polymer flooding process, the loss of polymer is smaller than that of surfactant, the dimensionless breakthrough time of polymer is 1.092 while that of surfactant is 1.308, and the dimensionless equal concentration distance of the chemical is 0.65. During surfactant-polymer flooding, the concentration of surfactant controls the formation of the emulsion. From 50 cm to 600 cm, as the migration distance increases, the concentration of surfactant decreases, and the emulsification strength and duration decrease gradually. With the formation of emulsion, the viscosity of the emulsion is relatively stable, which is beneficial to enhanced oil recovery. With the shear of reservoirs and migration of surfactant-polymer slug, the emulsion is formed to improve the swept volume and sweep efficiency and enhance oil recovery.

Emulsions in porous media: From single droplet behavior to applications for oil recovery

Emulsions are suspensions of droplets ubiquitous in oil recovery from underground reservoirs. Oil is typically trapped in geological porous media where emulsions are either formed in situ or injected to elicit oil mobilization and thus enhance the amount of oil recovered. Here, we briefly review basic concepts on geometrical and wetting features of porous media, including thin film stability and fluids penetration modes, which are more relevant for oil recovery and oil-contaminated aquifers. Then, we focus on the description of emulsion flow in porous media spanning from the behaviour of single droplets to the collective flow of a suspension of droplets, including the effect of bulk and interfacial rheology, hydrodynamic and physico-chemical interactions. Finally, we describe the particular case of emulsions used in underground porous media for enhanced oil recovery, thereby discussing some perspectives of future work. Although focused on oil recovery related topics, most of the insights we provide are useful towards remediation of oil-contaminated aquifers and for a basic understanding of emulsion flow in any kind of porous media, such as biological tissues.

Non-Fickian transport in porous media with bimodal structural heterogeneity

Tracer tailing in breakthrough curves in porous media with two distinct porosities is analyzed in terms of the dynamic responses of experimental fixed bed columns filled either with solid or porous beads. The flow is fast in the column interstitial space between beads (for both solid and porous beads) but slow within the porous beads that act as controlled 'traps' constituting an immobile zone. The transport is quantified using a Continuous Time Random Walk (CTRW) framework, which accounts for domains with controlled structural and flow heterogeneity associated with two distinct spatial and time spectra. We first demonstrate that breakthrough curves for a column containing solid glass beads exhibit non-Fickian transport, quantifiable both in fitting and validation mode by a CTRW based on a power law transition time distribution. We then examine breakthrough curves in the porous bead case, obtaining fits with a two-scale CTRW model that accounts explicitly for the two time spectra. Because the porous beads are uniform, tracer trapping within them is described by a simple first-order approximation trap model, with relatively weak capture and relatively faster release rates. The extent of tailing apparent in the porous bead breakthrough curves, due to the traps, can be quantitatively distinguished from the contribution to tailing due to mobile zone non-Fickian transport. A parameter study of the two-scale CTRW adds further insight into the dynamics of the process, showing the interaction between the advective non-Fickian transport and the mass exchange to immobile regions.

Replacing synthetic with microbial surfactants as collectors in the treatment of aqueous effluent produced by acid mine drainage, using the dissolved air flotation technique

Dissolved air flotation (DAF) is a well-established separation process employing micro bubbles as a carrier phase. The application of this technique in the treatment of acid mine drainage, using three yeast biosurfactants as alternative collectors, is hereby analyzed. Batch studies were carried out in a 50-cm high acrylic column with an external diameter of 2.5 cm. High percentages (above 94%) of heavy metals Fe(III) and Mn(II) were removed by the biosurfactants isolated from Candida lipolytica and Candida sphaerica and the values were found to be similar to those obtained with the use of the synthetic sodium oleate surfactant. The DAF operation with both surfactant and biosurfactants, achieved acceptable turbidity values, in accordance with Brazilian standard limits. The best ones were obtained by the biosurfactant from C. lipolytica, which reached 4.8 NTU. The results obtained with a laboratory synthetic effluent were also satisfactory. The biosurfactants removed almost the same percentages of iron, while the removal percentages of manganese were slightly higher compared with those obtained in the acid mine drainage effluent. They showed that the use of low-cost biosurfactants as collectors in the DAF process is a promising technology for the mining industries.