Direct measurement of the contact angle of water droplet on quartz in a reservoir rock with atomic force microscopy

Molecular Insight into CO2 Improving Oil Mobility in Shale Inorganic Nanopores Containing Water Films

CO2 injection into shale reservoirs has been recognized as one of the most promising techniques for enhanced oil recovery and carbon capture, utilization, and storage. However, the omnipresent nanopores and the water films formed near the pore walls affect the understanding of mechanisms of CO2 regulating crude oil mobility in shale nanopores. In this work, we employ molecular dynamics simulations to study the occurrence and flow of CO2 and octane (nC8) mixtures in quartz nanopores containing water films, to illustrate the impact mechanisms of CO2 on nC8 mobility. The results indicate that nC8 exists between water films, and CO2 is mainly miscible with nC8 in the pore center, and a small portion of it accumulates at the interface between nC8 and the water film. CO2 significantly decreases the apparent viscosity of nC8 in both the bulk nC8 region and the nC8-water interface region, improving nC8 fluidity. As the percentage of CO2 in the CO2 and nC8 mixtures increases from 0 to 50%, the mean flow velocities of nC8 in the bulk phase region and the nC8-water interface region increase by 92.85 and 60.64%, respectively. Three major microscopic mechanisms of CO2 improving nC8 fluidity in quartz nanopores with water films are summarized: (i) CO2 reduces friction between nC8 and the water film by increasing the angle between nC8 molecules and the plane of the water film; (ii) CO2 widens the distance between nC8 molecules, causing the volume expansion of nC8 and its viscosity reduction; (iii) CO2 significantly increases the most probable and average velocities of nC8 molecules, thus improving their mobility. Our results enhance the comprehension of how CO2 facilitates oil flow in water-bearing shale reservoirs and the exploitation of unconventional oil resources.

Monodispersed Bubble Generation Using Hydrophobic Orifices: The Extended Tate's Law

The use of submerged orifices for bubble generation is ubiquitous in industries with wettability known to influence the bubble departure diameter. In this study, we investigated bubble generation and departure from the orifices (0.3-2 mm) drilled on hydrophobic perfluoroalkoxy (PFA) tubes in water. By varying the gas inflow rate (33 to 200 mL/min), we found that the Sauter mean diameter closely matched those generated by hydrophilic quartz orifices. However, monodispersed bubbles were formed on the PFA tube compared to those on quartz with much wider size distributions. By examining the dynamic bubbling process, we confirmed its agreement with Tate's law, which was originally developed for quasi-steady conditions and emphasizes a balance between capillary and buoyancy forces. However, it should be noted that dynamic conditions lead to an increase in bubble volume compared to the quasi-steady condition despite following the same principle, which is explained by the continuous gas inflow when the bubble departs from the orifice at a necking stage. The above understandings enable generation of monodispersed bubbles under dynamic conditions, benefiting industries requiring precise control on bubble size, such as the bubble assisted wet etching and cleaning processes in semiconductor fabrication.

Method for Measuring the Three-Dimensional Morphology of Near-Wall Bubbles and Droplets Based on LED Digital Holography

Digital holography, recognized for its noncontact nature and high precision in three-dimensional imaging, is effectively employed to measure the morphology of bubbles and droplets. However, in terms of near-wall bubbles and droplets, such as confined bubbles in microfluidic chips, the measurement of the interface morphology of bubbles near the glass surface has not yet been resolved due to the coherent noise resulting from glass surface reflections in microfluidic chips. Accordingly, an off-axis digital holography system was devised by using Linnik interferometry. Measuring the confined bubble interface near the wall within a microfluidic chip and droplet evaporation on solid surfaces was studied. Partially coherent LED sources and reference light modulation techniques were employed in the optical setup to mitigate the coherent noise. Dual exposure and weighted least-squares unwrapping algorithms were introduced to correct phase distortions, enhancing image quality. Imaging two confined CO2 bubbles was done near the wall in silicon oil within a porous microfluidic chip, and contact angles of 4.7 and 4.5° were measured. Additionally, the measurement of the three-dimensional morphology of vertically evaporating deionized water droplets on a glass surface was done, due to which calculation of contact angles at various orientations was possible. This work offers a feasible new method for measuring the 3D interface morphology of bubbles and droplets, particularly in microfluidic visualization, addressing current measurement gaps.

Langmuir-Blodgett Films of Arachidic and Stearic Acids as Sensitive Coatings for Chloroform HF SAW Sensors

Properties of the Langmuir-Blodgett (LB) films of arachidic and stearic acids, versus the amount of the films' monolayers were studied and applied for chloroform vapor detection with acoustoelectric high-frequency SAW sensors, based on an AT quartz two-port Rayleigh type SAW resonator (414 MHz) and ST-X quartz SAW delay line (157.5 MHz). Using both devices, it was confirmed that the film with 17 monolayers of stearic acid deposited on the surface of the SAW delay line at a surface pressure of 30 mN/m in the solid phase has the best sensitivity towards chloroform vapors, compared with the same films with other numbers of monolayers. For the SAW resonator sensing using slightly longer arachidic acid molecules, the optimum performance was reached with 17 LB film layers due to a sharper decrease in the Q-factor with mass loading. To understand the background of the result, Atomic Force Microscopy (AFM) in intermittent contact mode was used to study the morphology of the films, depending on the number of monolayers. The presence of the advanced morphology of the film surface with a maximal average roughness (9.3 nm) and surface area (29.7 µm²) was found only for 17-monolayer film. The effects of the chloroform vapors on the amplitude and the phase of the acoustic signal for both SAW devices at 20 °C were measured and compared with those for toluene and ethanol vapors; the largest responses were detected for chloroform vapor. For the film with an optimal number of monolayers, the largest amplitude response was measured for the resonator-based device. Conversely, the largest change in the acoustic phase produced by chloroform adsorption was measured for delay-line configuration. Finally, it was established that the gas responses for both devices coated with the LB films are completely restored 60 s after chamber cleaning with dry air.

Review on the Test Methods and Devices for Mechanical Properties of Hydrate-Bearing Sediments

Commercial exploitation of marine natural gas hydrate (NGH) is crucial for energy decarbonization. However, hydrate production would weaken reservoir mechanical properties and trigger geohazards. Experimental instruments are the basis to obtain the mechanical responses of hydrate-bearing sediments (HBS). Considering the reservoir deformation processes from elastic deformation to residual deformation during hydrate exploitation, this study comprehensively reviewed the feasibility and mechanical research progress of the bender element, resonance column, atomic force microscope, triaxial shear, direct shear, ring shear, and static penetration in mechanical testing. Each test method’s precision and sample size were comprehensively compared and analyzed. Finally, the limitations and challenges of the current mechanical testing methods for HBS were discussed, and their future development directions were proposed. The proposed development direction in mechanical testing methods is expected to provide insightful guidance for the development of instruments and improve the understanding of the mechanical behavior of HBS.

Characterization of Ultrasonic-Induced Wettability Alteration under Subsurface Conditions

Understanding and manipulating wettability alterations has tremendous implications in theoretical research and industrial applications. This study proposes a novel idea of applying ultrasonic for wettability alterations and also provides its quantitative characterizations and in-depth analyses. More specifically, with pretreatment of ultrasonic, mechanisms of wettability alteration were characterized from the contact angle measurements, as well as the in-depth analyses from atomic force microscopy (AFM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). After ultrasonic treatments, the wettability of mineral with low permeability is determined to altered from strong hydrophilic to intermediate wettability. The mechanism interpretations are conducted by means of the AFM, XRD, and FTIR. Basically, as the time of ultrasonic treatment increases, the AFM results indicate that the roughness of rock surface and oil/rock interface (contact area) with surroundings of brine is enhanced. Meanwhile, the XRD results show the diffusions of clays from the rock surface to the aqueous phase, and FTIR indicates that the number of functional groups of Si-O-Si, C-O-C, C-O, C═O, and OH decreases while the number of COOH and C═C═O groups increases. This study clearly reveals the surface chemistry of oil-rock wettability alteration in the subsurface conditions, which would provide technical support for subsurface usage of geo-energy productions and carbon sequestrations.

Crystal face dependent wettability of α-quartz: Elucidation by time-of-flight secondary ion mass spectrometry techniques combined with molecular dynamics

HYPOTHESIS

Quartz is one of the most common but important minerals, and its wettability plays a significant role in affecting various natural and industrial processes. Studies have revealed that different crystal faces of quartz are with different wettabilities, but its mechanism is still vague.

EXPERIMENTS AND SIMULATIONS

For specifying the mechanism of crystal face dependent wettability, the contact angles of three different liquids on the crystal faces of α-quartz are measured; the time-of-flight secondary ion mass spectrometry (ToF-SIMS) is employed to establish the crystal surface models; molecular dynamics (MD) simulations with the surface models are performed to understand the wetting behavior at molecular scale.

FINDINGS

Based on the contact angle measurements, the wettabilities of different crystal faces of α-quartz are found different, which can be directly attributed to the concentration of hydroxyl group on crystal faces based on ToF-SIMS results. MD simulations yield consistent results with the contact angle order recognized from experiments, revealing that the surface hydroxyl group controls the wettability of α-quartz crystal faces. It is also recognized that the pristine surface atomic arrangement, especially the surface concentration of unsaturated bond (an intrinsic property of α-quartz), is the intrinsic cause of the difference in the concentration of hydroxyl group of the crystal surface.

Atomic force microscopy for the characterisation of pinning effects of seawater micro-droplets in n-decane on a calcite surface

HYPOTHESIS

Roughness is an important parameter in applications where wetting needs to be characterized. Micro-computed tomography is commonly used to characterize wetting in porous media but the main limitation of this approach is the incapacity to identify nanoscale roughness. Atomic force microscopy, AFM, however, has been used to characterize the topography of surfaces down to the molecular scale. Here we investigate the potential of using AFM to characterize wetting behavior at the nanoscale.

EXPERIMENTS

Droplets of water on cleaved calcite under decane were imaged using quantitative imaging QI atomic force microscopy where a force-distance curve is obtained at every pixel.

FINDINGS

When the AFM tip passed through the water droplet surface, an attraction was observed due to capillary effects, such that the thickness of the water film was estimated and hence the profile of the droplet obtained. This enables parameters such as the contact angle and contact angle distribution to be obtained at a nanometer scale. The contact angles around the 3-phase contact line are found to be quasi-symmetrically distributed between 10-30°. A correlation between the height profile of the surface and contact angle distribution demonstrates a quasi-proportional relationship between roughness on the calcite surface and contact angle.

Thermo-osmosis in hydrophilic nanochannels: mechanism and size effect

Understanding thermo-osmosis in nanoscale channels and pores is essential for both theoretical advances of thermally induced mass flow and a wide range of emerging industrial applications. We present a new mechanistic understanding and quantification of thermo-osmosis at nanometric/sub-nanometric length scales and link the outcomes with the non-equilibrium thermodynamics of the phenomenon. The work is focused on thermo-osmosis of water in quartz slit nanochannels, which is analysed by molecular dynamics (MD) simulations of mechano-caloric and thermo-osmotic systems. We investigate the applicability of Onsager reciprocal relation, irreversible thermodynamics, and continuum fluid mechanics at the nanoscale. Further, we analyse the effects of channel size on the thermo-osmosis coefficient, and show, for the first time, that these arise from specific liquid structures dictated by the channel size. The mechanical conditions of the interfacial water under different temperatures are quantified using a continuum approach (pressure tensor distribution) and a discrete approach (body force per molecule) to elucidate the underlying mechanism of thermo-osmosis. The results show that the fluid molecules located in the boundary layers adjacent to the solid surfaces experience a driving force which generates the thermo-osmotic flow. While the findings provide a fundamental understanding of thermo-osmosis, the methods developed provide a route for analysis of the entire class of coupled heat and mass transport phenomena in nanoscale structures.

Methodology for Concurrent Multi-Parametric Physical Modeling of a Target Natural Unfractured Homogeneous Sandstone

In petroleum, geological and environmental science, flow through porous media is conventionally studied complementarily with numerical modeling/simulation and experimental corefloods. Despite advances in numerical modeling/simulation, experimental corefloods with actual samples are still desired for higher-specificity testing or more complex mechanistic studies. In these applications, the lack of advances in physical modeling is very apparent with the available options mostly unchanged for decades (e.g., sandpacks of unconsolidated packing materials, industry-accepted substitutes with fixed/mismatching petrophysical properties such as Berea sandstone). Renewable synthetic porous media with adjustable parameters are the most promising but have not advanced adequately. To address this, a methodology of advanced physical modeling of the fundamental parameters of dominant mineralogy, particle size distribution, packing, and cementation of a target natural porous media is introduced. Based upon the tight physical modeling of these four fundamental parameters, the other derived parameters of interests including wettability, porosity, pore throat size distribution, permeability, and capillary pressure can be concurrently modeled very close as well by further fine-tuning one of the fundamental parameters while holding the rest constant. Through this process, concurrent multi-parametric physical modeling of the primary petrophysical parameters including particle size distribution, wettability, porosity, pore throat size distribution, permeability, capillary pressure behavior in a target sandstone becomes possible.

Experimental Investigation of the Role of DC Voltage in the Wettability Alteration in Tight Sandstones

The usage of direct current (DC) voltage has enormous potential for oil fields due to the effect of wettability alteration. However, the unclear mechanism of the wettability alteration has limited the application of this technology to oil fields. In this study, chemical and physical methods including contact angle tests, Fourier-transform infrared spectroscopy (FTIR) measurements, and atomic force microscope (AFM) experiments were combined to investigate the wettability alteration mechanism for tight sandstones subjected to DC voltage treatment. From the view of a chemical factor, FTIR results show that DC voltage decreases the number of Si-O-Si, C-O-C, C-O, and COOH groups, while it also increases the number of C═O and OH groups. The changes in molecular groups further improve the water-wetting property of tight sandstones. On the other hand, in a physical way, AFM results indicate that DC voltage improves the roughness of the rock surface. At the same time, the wetting state transfers from the Cassie-Baxter to the Wenzel. This increases the contact area of the solid-liquid interface. The augment of roughness and the transfer of the wetting state improve the water-wetting property of tight sandstones. By comparing the influences of both chemical and physical factors on wettability, it is concluded that although roughness indeed affects the wettability, chemical factors play a dominant role in determining the wettability. Achievements in this study can help researchers and engineers better understand the mechanism of wettability alteration and further accelerate the development of tight sandstones with DC voltage-related technology.

Insights into Nanoscale Wettability Effects of Low Salinity and Nanofluid Enhanced Oil Recovery Techniques

In this study, enhanced oil recovery (EOR) techniques—namely low salinity and nanofluid EOR—are probed at the nanometer-scale using an atomic force microscope (AFM). Mica substrates were used as model clay-rich rocks while AFM tips were coated to present alkyl (-CH3), aromatic (-C6H5) and carboxylic acid (-COOH) functional groups, to simulate oil media. We prepared brine formulations to test brine dilution and cation bridging effects while selected concentrations (0 to 1 wt%) of hydrophilic SiO2 nanoparticles dispersed in 1 wt% NaCl were used as nanofluids. Samples were immersed in fluid cells and chemical force mapping was used to measure the adhesion force between polar/non-polar moieties to substrates. Adhesion work was evaluated based on force-displacement curves and compared with theories. Results from AFM studies indicate that low salinity waters and nanoparticle dispersions promote nanoscale wettability alteration by significantly reducing three-phase adhesion force and the reversible thermodynamic work of adhesion, also known as adhesion energy. The maximum reduction in adhesion energy obtained in experiments was in excellent agreement with existing theories. Electrostatic repulsion and reduced non-electrostatic adhesion are prominent surface forces common to both low salinity and nanofluid EOR. Structural forces are complex in nature and may not always decrease total adhesion force and energy at high nanoparticle concentration. Wettability effects also depend on surface chemical groups and the presence of divalent Mg2+ and Ca2+ cations. This study provides fresh insights and fundamental information about low salinity and nanofluid EOR while demonstrating the application of force-distance spectroscopy in investigating EOR techniques.

The Attraction of Water for Itself at Hydrophobic Quartz Interfaces

Structural forces within aqueous water at a solid interface can significantly change surface reactivity and the affinity of solutes toward it. We show using molecular dynamics simulations how hydrophilic and hydrophobic quartz surfaces perturb the orientational structure of aqueous water, ultimately strengthening dipolar forces between molecules in proximity to the interface. When derived as a function of distance from each surface, it was found that both surfaces indirectly enhance the long-range dipolar attraction of water for itself toward the interfacial region. This was found to be longer-ranged for water molecules solvating the hydrophobic surface than those solvating the hydrophilic surface, with a range of up to 2.5 nm from the hydrophobic surface. Our results give direct quantification of surface-induced changes in solvent-solvent attraction, ultimately providing a counterintuitive addition to the balance of hydrophobic forces at aqueous-solid interfaces.

From Contact Line Structures to Wetting Dynamics

An important reason for the century-long debate concerning wetting dynamics is the lack of decisive information about the contact line. The contact line cannot be treated as a geometric line but is rather a region with complex structures. The contact line regions have been intensively explored in recent years by utilizing advanced nanoscopic experimental and modeling methods. This feature article summarizes the primary observation results and related modeling progress. A framework is then proposed for understanding the wetting dynamics. Basic questions are raised for future research on the partial wetting of nonvolatile as well as volatile liquids.

Effect of Aggregation and Adsorption Behavior on the Flow Resistance of Surfactant Fluid on Smooth and Rough Surfaces: A Many-Body Dissipative Particle Dynamics Study

To study the effect of surfactant on the resistance of wall-bound flow, the adsorption and aggregation behaviors of surfactant fluid on both smooth and groove-patterned rough surface are investigated through many-body dissipative particle dynamics (MDPD) simulation. The MDPD models of surfactants were carefully parametrized and have been validated to be able to simulate the aggregation and adsorption behavior of surfactants. The simulation results show that the surfactant in laminar flow can only increase the flow resistance on the smooth surface. On the rough surface, surfactant with strong adsorption performance on the channel wall shows a drag reduction effect at moderate concentration. The surfactant with weak adsorption properties can enhance the flow resistance, which is even more significant than that of those surfactants with no adsorption capacity. Although heating (high temperature) can generally reduce the viscosity and flow resistance of surfactant fluid, it would cause a poor drag reduction efficiency. It may arise from the destruction of the adsorption layer and the interruption of the fluid/boundary interface. Surfactant adsorption can tune the roughness of the fluid boundary on either the smooth or rough surface in a different manner, which turns out to be highly correlated to the change in flow resistance. Compared with the adsorption layer, surfactant in the bulk fluid makes a greater contribution to enhancing the flow resistance as the concentration rises. This study is expected to be helpful in guiding the application of surfactants on the micro- and nanoscale such as lab-on-a-chip nanodevices and EOR in a low-permeability porous medium.

Solid-Liquid-Liquid Wettability of Surfactant-Oil-Water Systems and Its Prediction around the Phase Inversion Point

Surfactant-oil-water (SOW) systems are important for numerous applications, including hard surface cleaning, detergency, and enhanced oil-recovery applications. There is limited literature on the wettability of solid-liquid-liquid (SLL) systems around the surfactant phase inversion point (PIP), and the few references that exist point to wettability inversion accompanying the microemulsion (μE) phase inversion. Despite the significance of this phenomenon and the extreme changes in contact angles, there are no models to predict SLL wettability as a function of proximity to the PIP. Recent works on SLL wettability in surfactant-free systems suggest that SLL contact angles can be predicted with an extension of Neumann's equation of state (e-EQS) if the interfacial tension (IFT or γ_o-w) is known and if there is a good estimate for the interfacial energy between the wetting phase and the surface (γ_{S-wetting liquid}). In this work, IFT predictions for SOW systems around the PIP were obtained via the combined hydrophilic-lipophilic difference (HLD) and net-average-curvature (NAC) framework. To test the hypothesis that the combined HLD-NAC + e-EQS can predict wettability inversion around the PIP, with a given γ_S-μE, the contact angles (measured through the light oil phase, θ_O) for the μE of sodium dihexyl sulfosuccinate-toluene-saline water system were measured on high surface free energy (SFE) materials (glass, stainless steel, and mica) and on polytetrafluoroethylene (low SFE) around the PIP. Considering that at the PIP, most systems have a contact angle of 90°, an estimated γ_S-μE = 1/4γ_o-w@PIP was found to be suitable for the systems considered in this work and for systems presented in the literature. The largest deviations between the predictions and the experimental values were found in the positive HLD range (surfactant in the light oil phase). Although there is room for improvement, this framework can estimate the wetting behavior of SOW systems starting solely from formulation parameters.