Dynamics of foam flow in a rock fracture: Effects of aperture variation on apparent shear viscosity and bubble morphology

There has recently been renewed interest in understanding the physics of foam flow in permeable media. As for Newtonian flows in fractures, the heterogeneity of local apertures in natural fractures is expected to strongly impact the spatial distribution of foam flow. Although several experimental studies have been previously performed to study foam flow in fractured media, none of them has specifically addressed that impact for parallel flow in a realistic fracture geometry and its consequences for the foam’s in situ shear viscosity and bubble morphologies. To do so, a comprehensive series of single-phase experiments have been performed by injecting pre-generated foams with six different qualities at a constant flow rate through a replica of a Vosges sandstone fracture of well-characterized aperture map. These measurements were compared to measurements obtained in a Hele-Shaw (i.e., smooth) fracture of identical hydraulic aperture. The results show that fracture wall roughness strongly increases the foam’s apparent viscosity and shear rate. Moreover, foam bubbles traveling in regions of larger aperture exhibit larger velocity, size, a higher coarsening rate, and are subjected to a higher shear rate. This study also presents the first in situ measurement of foam bubbles velocities in fracture geometry, and provides hints towards measuring the in situ rheology of foam in a rough fracture from the velocity maps, for various imposed mean flow rates. These findings echo the necessity of considering fracture wall when predicting the pressure drop through the fracture and the effective viscosity, as well as in situ rheology, of the foam

Localized Delivery of Liquid Fertilizer in Coarse-Textured Soils Using Foam as Carrier

Agrochemicals and fertilizers are central to modern agriculture and are credited with the large increase of crop yield as a part of the Green Revolution of the 1960's. Timely and targeted fertilizer application to crop root zones enhances effectiveness and reduces unintended release to the environment. This is particularly important for highly mobile liquid fertilizers (e.g., nitrate) that can be mobilized with infiltrating water to bypass root-bearing soil volumes. We report a novel liquid fertilizer delivery method using foam as carrier. The high degree of control and mechanical stability of liquid fertilizer foam (defined dispersed gas bubbles in a continuous liquid phase) injection into coarse soils (most susceptible to preferential flows) is proposed a novel delivery method to targeted root zone volumes at concentrations and geometry that promote uptake and reduces losses. This note and preliminary communication meant to serve a proof of concept report comparing foam and conventional liquid fertilizer applications. The results indicate that foam-delivery reduced fertilizer leaching thus improving its retention in soil for similar flow conditions of liquid delivery. Theoretical estimates suggest that the effects of fertilizer retention could be enhanced in more localized (3-D) injection of foam fertilizers and other agrochemicals thus enhancing agronomic efficiency and reducing environmental risk of contamination.ISSN:0169-3913ISSN:1573-163

An Estimation of Wave Attenuation Factor in Ultrasonic Assisted Gravity Drainage Process

It has been proved that ultrasonic energy can considerably increase the amount of oil recovery in an immiscible displacement process. Although many studies have been performed on investigating the roles of ultrasonic waves, based on the best of our knowledge, little attention has been paid to evaluate wave attenuation parameter, which is an important parameter in the determination of the energy delivered to the porous medium. In this study, free fall gravity drainage process is investigated in a glass bead porous medium. Kerosene and Dorud crude oil are used as the wetting phases and air is used as the non-wetting phase. A piston-like displacement model with considering constant capillary pressure and applying Corey type approximation for relative permeabilities of both wetting and nonwetting phases is applied. A pressure term is considered to describe the presence of ultrasonic waves and the attenuation factor of ultrasonic waves is calculated by evaluating the value of external pressure applied to enhance the flow using the history matching of the data in the presence and absence of ultrasonic waves. The results introduce the attenuation factor as an important parameter in the process of ultrasonic assisted gravity drainage. The results show that only a low percentage of the ultrasonic energy (5.8% for Dorud crude oil and 3.3% for kerosene) is delivered to the flow of the fluid; however, a high increase in oil recovery enhancement (15% for Dorud crude oil and 12% for Kerosene) is observed in the experiments. This proves that the ultrasonic waves, even when the contribution is not substantial, can be a significantly efficient method for flow enhancement

Foam flow investigation in 3D printed porous media: Fingering and gravitational effects

Flow in porous media investigations have shown foam injection have a higher sweep efficiency compare to gas injection. However, fingering of highly mobile gas into the foam bank and separation of fluids (gas and surfactant) resulted by gravity segregation can influence the performance of foam injection project. To the best of our knowledge, this phenomenon has not been investigated experimentally in the literature. In this study, foam injection experiments have been performed in a model oriented in a horizontal and perpendicular orientation with respect to gravity using also different flow rates. High resolution imaging tools were utilized to record displacement process of oil by gas/surfactant/foam. The recorded images enabled us to monitor gas fingering and foam flow dynamics at pore scale. The obtained results highlighted the adverse effect of fingering of highly mobile gas into the foam bank and fluids separation by gravity segregation in the performance of foam project

Combined Effects of Nanoparticles and Surfactants upon Foam Stability

International audienceWe investigate effects of surfactants with different charges (anionic, cationic, and non-ionic) on foam stability in the presence of charge-stabilized silica (SiO2) nanoparticles. Toward this aim, a comprehensive series of experiments on a Hele-Shaw cell and a foam column is conducted at bubble and bulk-scale respectively, that is, investigating phenomenologies of foam coarsening separately by gas diffusion and bubble coalescence, and by gravitational drainage. Our results show nanoparticles, despite their ability to position themselves at liquid-gas interfaces and thus limit the resulting surface tension coefficient, do not necessarily have a positive effect on foam stability; the nature and magnitude of this effect depends strongly on the nature of the surfactant, its concentration and the concentration of nanoparticles. In less stable systems, significant coarsening occurs. Both results from bubble-scale and the bulk-scale experiments suggest that compatibility experiments are pre-requisite to foam stability analysis to test the compatibility between surfactants and nanoparticles

Low Frequency Electrical Stimulation Attenuated The Epileptiform Activity-Induced Changes in Action Potential Features in Hippocampal CA1 Pyramidal Neurons

Objective Electrical low frequency stimulation (LFS) is a new therapeutic method that moderates hyperexcitability during epileptic states. Seizure occurrence is accompanied by some changes in action potential (AP) features. In this study, we investigated the inhibitory action of LFS on epileptiform activity (EA) induced-changes in AP features in hippocampal CA1 pyramidal neurons. Materials and Methods In this experimental study, we induced EA in hippocampal slices by increasing the extracellular potassium (K+) concentration to 12 mM. LFS (1 Hz) was applied to the Schaffer collaterals at different pulse numbers (600 and 900) at the beginning of the EA. Changes in AP features recorded by whole-cell patch clamp recording were compared using phase plot analysis. Results Induction of EA depolarized membrane potential, decreased peak amplitude, as well as the maximum rise and decay slopes of APs. Administration of 1 Hz LFS at the beginning of EA prevented the above mentioned changes in AP features. This suppressive effect of LFS depended on the LFS pulse number, such that application of 900 pulses of LFS had a stronger recovery effect on AP features that changed during EA compared to 600 pulses of LFS. The constructed phase plots of APs revealed that LFS at 900 pulses significantly decreased the changes in resting membrane potential (RMP), peak amplitude, and maximum rise and decay slopes that appeared during EA. Conclusion Increasing the numbers of LFS pulses can magnify its inhibitory effects on EA-induced changes in AP features

Foam generation and stability : role of the surfactant structure and asphaltene aggregates

Understanding how the surfactant molecular structure affects foam stability is important in various applications, such as soil remediation, the food industry, enhanced oil recovery, and hydraulic fracturing. In this study, we conduct a systematic series of experiments in a Hele-Shaw cell to assess and explain the effect of surfactants on foamability and foam stability in the absence and presence of oil and asphaltene aggregates. Four surfactants with different molecular weights were studied, including three anionic surfactants, sodium 1,5-bis[(1H,1H,2H,2H-perfluorohexyl)oxy]-1,5-dioxopentane-2-sulfonate (FG4), C18H37SO4Na (LSES), and sodium dodecyl sulfate (SDS), and one cationic surfactant (CTAB, (C16H33NMe3)Br). We observed that the higher electrostatic repulsion between the foam film surfaces for the anionic surfactants (FG4 > LSES > SDS) strongly influences the process of foam generation and stability when compared with the cationic surfactant (CTAB). For example, the foam coarsening rate for CTAB was 700% higher than that for FG4 when we performed experiments in an empty Hele-Shaw cell. Furthermore, the foam experiments performed in the presence of oil revealed maximum long-term stability and minimum bubble coarsening for the partially fluorinated FG4 surfactant. The experiments in the presence of asphaltene-oil mixtures revealed that the latter has a detrimental effect on foam stability, except for FG4. The foam experiments clearly show the significance of the subtle interactions between the surfactant headgroup charge, chain length, and branching. The obtained results could be useful in designing appropriate surfactants for foam stabilization in various applications