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The utilization (absorption and areal sweep) of injected carbon dioxide (CO 2) can be enhanced if a viscous and agglomeration free nanofluid is used as most of the nanoparticles (NPs) prefer to stay in bulk phase rather than adsorbing on CO 2 surface. NP adsorption can be improved if non-participating NPs are surface modified with a suitable surface modifying agent e.g. , triethoxy (vinyl)silane (TVS). Thus, in this study, single-step approach was used to synthesize agglomeration free TiO 2 nanofluid whose surface modification was carried out in varying proportion of TVS (1–5% v/v) followed by the discussion on comparative CO 2 absorption and storage performance by different tools such as DLS, IFT, Rheology, Contact-angle, and Micromodel flow. The basic nanofluid (T o) showed greater CO 2 absorption after surface modification as demonstrated by molality results. However, surface modification also decreased dispersion stability of surface modified nanofluids (T 1 , T 2 , and T 3) and T 2 was regarded as the most stable nanofluid with −64.4 mV (ζ-potential) and 153 nm (NP size). After surface modification, increase in NP size and settlement was higher for surface modified nanofluids than T o , which exhibited dispersion stability of 84 d with −53.4 mV and 15 nm. Contact angle results also showed that surface modified nanofluids possess greater affinity for CO 2 absorption than basic nanofluid (T o). Rheological analysis was also consistent with other tests where viscosity was found dependent on both storage period and temperature, and NP settlement was found to be the most influential parameter on flow properties of nanofluid. Finally, pore scale analysis was performed to understand areal sweep of injected CO 2 in micromodel with and without nanofluid, where nanofluid imparted greater CO 2 storage by diverting it in un-swept pore networks of micromodel which were untapped by CO 2 without nanofluid. • Surface modified single-step TiO 2 nanofluid was used for CO 2 absorption and storage. • The size and dispersion stability of nanofluid was dependent on surface modifying agent. • Rheological property of nanofluids was investigated as a function of time and temperature. • Nanofluids showed least wetting on rock surface after surface modification. • Micromodels were used to envisage CO 2 storage with/without nanofluid at pore scale. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new approach is developed for dynamically evaluating asphaltene deposition in carbonate rocks. • The evaluation of calcite surface wettability is carried out through contact angle and micromodel tests. • The crude oil properties are determined using DHA and FTIR tests together. • Asphaltene molecular-structural properties are assessed using elemental analysis, FESEM, NMR, and FTIR techniques. • The contact angle test and micromodel experiments are done simultaneously. Asphaltene deposition in the porous media of the reservoir during the production life causes serious challenges with significant economic cost. From the point of view of proactive action to prevent the formation of such precipitates, today asphaltene inhibitors are widely used in the oil industry. The successful performance of inhibitors strongly depends on molecular structure of asphaltene. This study investigates the effect of molecular-structural properties of asphaltene in four crude oil samples on calcite surface wettability. The wettability of the calcite surface is evaluated with contact angle test and micromodel. The crude oil properties are determined using DHA (Detailed Hydrocarbon Analysis) and FTIR (Fourier Transform Infrared Spectroscopy) tests, while the molecular-structural properties of asphaltene are assessed using elemental analysis, FESEM (Field Emission Scanning Electron Microscopy), NMR (Nuclear Magnetic Resonance), and FTIR techniques. Based on FTIR analysis of oil samples, the higher polarity of samples B and G compared to samples F and A can be attributed to the presence of C = O carboxylic acid stretches. In addition, DHA analysis indicates that sample B, which contains heavier compounds comprising 27.4220 % of the C 14 + compounds by weight, exhibits distinct characteristics. The FESEM images demonstrate a uniform and smooth spread surface morphology of the asphaltene samples. However, the elemental analysis does not establish a correlation between the heteroelement ratios of N/C, O/C, and S/C and asphaltene adsorption tendency. FTIR and NMR analyses suggest that the wetting properties observed on the surface are mainly attributed to the high aromatic and aliphatic compounds present in the asphaltene of sample B, while the polar compounds are less influential. The results reveal that crude oil sample B exhibits the highest percentage of damage to the porous medium caused by asphaltene deposition, with a rate of 36.18 % and a contact angle of 163.53 degrees. This indicates a wetter surface of the oil compared to other samples. Samples G and A follow with contact angles of 157.34° and 153.60°, respectively. On the other hand, sample F shows the lowest wettability change on the calcite surface with a contact angle of 144.77° and only 0.08 % damage to the porous medium. [ABSTRACT FROM AUTHOR]

Microwave (MW) absorption ability of Fe3O4 nanoparticles was increased by attaching NiO nanomaterials to them through a co-precipitation approach. The surface of the synthesized nanohybrids was hydrophilized using three different natural agents to disperse in water. The synthesized nanohybrids were characterized by several analyses. The colloidal stability, magnetic behavior and the effect of surface modification agent on the MW absorption ability of the synthesized nanohybrids were investigated. The ability of surface-modified nanohybrids to increase the oil recovery factor was studied by injecting them into a 2D glass micromodel as the porous medium. The results showed that CA is the best modification agent with high colloidal stability strong MW absorption and the lowest effect on the reduction of magnetic saturation of uncoated nanohybrids. Citric acid decreased the saturation magnetization from 55.43 emu/gr at the uncoated state to 52.82 emu/gr at the modified state. The oil sample with more polar compounds such as asphaltene could be further heated and its viscosity further reduced in an EM heating process. By adding 0.1 wt% of the Fe3O4-NiO nanohybrids, the viscosity of sample (S1) was reduced by 266 mPa·s more than the MW radiation state alone. The findings indicate that MW radiation can significantly increase the heavy oil recovery factor. Water injection had only 16.6% oil recovery; however, this value increased to 41.5% by radiating 400 watts MW This increase will be further enhanced by adding modified Fe3O4-NiO nanohybrids to water. The Fe3O4-NiO @ CA, Fe3O4-NiO @ APTES, and Fe3O4-NiO @ PEG had 69%, 63.5%, and 58.3% oil recovery, respectively. Finally, it was found that the surface modified nanohybrids could change the wettability of the porous medium from oil-wet to water-wet. After coating the glass with the Fe3O4-NiO @ CA nanofluid, the oil contact angle decreased from 140° to 17°. [ABSTRACT FROM AUTHOR]

This study aims to elucidate the dynamics of fluid topology during drainage and evaporation of wetting and non-wetting fluids via evaluation of their Euler characteristic (EC) and Betti numbers from designed experiments. The results showed that the EC of the non-wetting fluid remained constant at a high wetting fluid saturation and then decreased nonlinearly. However, the EC of the wetting fluid exhibited more complex trends. In the 2-D micromodel, the number of loops decreased monotonously, reached zero, and remained constant for lower saturations, while the number of distinct components fluctuated because of the appearance and disappearance of disconnected clusters. In the 2-D model, the number of distinct components played a significant role; in the 3-D X-ray CT experiment, the number of loops of pendular rings dominated the EC. The findings suggest that the trends observed in the 2-D micromodel may not apply under 3-D conditions. [ABSTRACT FROM AUTHOR]

The capillary pressure‐saturation relation is one of the key constitutive equations used for modeling multiphase (or partially saturated) flow in porous materials. It is known that this empirical relation depends strongly on dynamic conditions, but the impact of a heterogeneity interface on this relationship has been studied less. The present study employed optical imaging to visualize two‐phase drainage under different injection rates and two flow directions, in a heterogeneous micromodel. By analyzing the curvatures of the fluid‐fluid interfaces, the averaged capillary pressures for the coarse and fine sections of the micromodel, and the entire micromodel were estimated. Results show that the capillary pressure‐saturation relation in the vicinity of a heterogeneity interface does not follow the conventional models proposed in the literature. The averaged capillary pressure over the entire micromodel for the fine‐to‐coarse (FtC) direction shows decreasing capillary pressure with decreasing wetting phase saturation. However, in the coarse‐to‐fine direction, a non‐monotonic trend was observed. These initial findings highlight the gaps in the knowledge of upscaling capillary pressure in heterogeneous porous materials. Moreover, discontinuity in saturation was clearly more pronounced for the FtC direction, as a result of lower entry capillary resistance against the flow in the coarse section. Key Points: Averaged capillary pressure‐saturation relation was estimated using image processing of microfluidic experimentsThe capillary pressure‐saturation relation varies significantly with the direction of flow with respect to the heterogeneityNonmonotonic capillary pressure‐saturation relations were observed in presence of a heterogeneity interface [ABSTRACT FROM AUTHOR]

Polymer injection is one method of chemical enhanced oil recovery, which increase oil recovery by improving mobility when viscous fingering occurred in waterflooding operation. The result of polymer injection is better sweep efficiency, which is presented by more even distribution of the injected fluid. However, in common laboratory evaluation for polymer injection testing, it was no visual observation that presents directly for the fluiddistribution. This experimental study was carried out to visually observe the polymer injection mechanism to displace oil by micromodel as porous media. The micromodel used in this study is transparent acrylic material which was etched by laser engraving technology to create grains that resemble reservoir rocks. The micromodel was saturated by brine water and light oil respectively as initial reservoir fluids. Then, the water was injected as waterflooding operation to displace oil in a micromodel. Hydrolyzed Polyacrylamide (HPAM) polymer with various concentrations were injected into the micromodel as the last scenario. Through this experiment, the movement and distribution of fluids in chemical enhanced oil recovery especiallypolymer injection was able to be recorded for further analysis. Observation for each scenario was done by Digital Image Analysis (DIA). The micromodel flooding results showed that the higher concentration of polymer would give higher oil recovery. The front stability and good distribution of polymer will result in better sweep efficiency, then higher oil recovery will be achieved. This experiment gives result visually how polymer enhance oil recovery. This experiment is expected to be leading innovation for Enhanced Oil Recovery (EOR) laboratory studies in Indonesia

In modeling of geological carbon storage, dissolution of supercritical CO2 (scCO2) is often assumed to be instantaneous with equilibrium phase partitioning. In contrast, recent core-scale imbibition experiments have shown a prolonged depletion of residual scCO2 by dissolution, implying a non-equilibrium mechanism. In this study, eight pore-scale scCO2 dissolution experiments in a 2D heterogeneous, sandstone-analog micromodel were conducted at supercritical conditions (9MPa and 40°C). The micromodel was first saturated with deionized (DI) water and drained by injecting scCO2 to establish a stable scCO2 saturation. DI water was then injected at constant flow rates after scCO2 drainage was completed. High resolution time-lapse images of scCO2 and water distributions were obtained during imbibition and dissolution, aided by a scCO2-soluble fluorescent dye introduced with scCO2 during drainage. These images were used to estimate scCO2 saturations and scCO2 depletion rates. Experimental results show that (1) a time-independent, varying number of water-flow channels are created during imbibition and later dominant dissolution by the random nature of water flow at the micromodel inlet, and (2) a time-dependent number of water-flow channels are created by coupled imbibition and dissolution following completion of dominant imbibition. The number of water-flow paths, constant or transient in nature, greatly affects the overall depletion rate of scCO2 by dissolution. The average mass fraction of dissolved CO2 (dsCO2) in water effluent varies from 0.38% to 2.72% of CO2 solubility, indicating non-equilibrium scCO2 dissolution in the millimeter-scale pore network. In general, the transient depletion rate decreases as trapped, discontinuous scCO2 bubbles and clusters within water-flow paths dissolve, then remains low with dissolution of large bypassed scCO2 clusters at their interfaces with longitudinal water flow, and finally increases with coupled transverse water flow and enhanced dissolution of large scCO2 clusters. The three stages of scCO2 depletion, common to experiments with time-independent water-flow paths, are revealed by zoom-in image analysis of individual scCO2 bubbles and clusters. The measured relative permeability of water, affected by scCO2 dissolution and bi-modal permeability, shows a non-monotonic dependence on saturation. The results for experiments with different injection rates imply that the non-equilibrium nature of scCO2 dissolution becomes less important when water flow is relatively low and the time scale for dissolution is large, and more pronounced when heterogeneity is strong.

In modeling of geological carbon storage, dissolution of supercritical CO2 (scCO2) is often assumed to be instantaneous with equilibrium phase partitioning. In contrast, recent core-scale imbibition experiments have shown a prolonged depletion of residual scCO2 by dissolution, implying a non-equilibrium mechanism. In this study, eight pore-scale scCO2 dissolution experiments in a 2D heterogeneous, sandstone-analog micromodel were conducted at supercritical conditions (9MPa and 40°C). The micromodel was first saturated with deionized (DI) water and drained by injecting scCO2 to establish a stable scCO2 saturation. DI water was then injected at constant flow rates after scCO2 drainage was completed. High resolution time-lapse images of scCO2 and water distributions were obtained during imbibition and dissolution, aided by a scCO2-soluble fluorescent dye introduced with scCO2 during drainage. These images were used to estimate scCO2 saturations and scCO2 depletion rates. Experimental results show that (1) a time-independent, varying number of water-flow channels are created during imbibition and later dominant dissolution by the random nature of water flow at the micromodel inlet, and (2) a time-dependent number of water-flow channels are created by coupled imbibition and dissolution following completion of dominant imbibition. The number of water-flow paths, constant or transient in nature, greatly affects the overall depletion rate of scCO2 by dissolution. The average mass fraction of dissolved CO2 (dsCO2) in water effluent varies from 0.38% to 2.72% of CO2 solubility, indicating non-equilibrium scCO2 dissolution in the millimeter-scale pore network. In general, the transient depletion rate decreases as trapped, discontinuous scCO2 bubbles and clusters within water-flow paths dissolve, then remains low with dissolution of large bypassed scCO2 clusters at their interfaces with longitudinal water flow, and finally increases with coupled transverse water flow and enhanced dissolution of large scCO2 clusters. The three stages of scCO2 depletion, common to experiments with time-independent water-flow paths, are revealed by zoom-in image analysis of individual scCO2 bubbles and clusters. The measured relative permeability of water, affected by scCO2 dissolution and bi-modal permeability, shows a non-monotonic dependence on saturation. The results for experiments with different injection rates imply that the non-equilibrium nature of scCO2 dissolution becomes less important when water flow is relatively low and the time scale for dissolution is large, and more pronounced when heterogeneity is strong.

Nanotechnology has the capability to modernize both the upstream and downstream oil and gas industry. It has been effectively used in exploration, drilling, production, refinery as well as in enhanced oil recovery (EOR) fields. Understanding the basics of scaling criteria development along with nanoparticle stabilized EOR mechanism will assist petroleum engineers in designing, analyzing, and evaluating nanoparticleassisted EOR techniques. This paper aims to deliver a critical review on nanoparticle-assisted EOR methods along with introducing scaling approaches and their applications in EOR. Scaling criteria can be employed to assess the performance of a specific EOR technique so that it can be accurately applied to the field scale. In this study, scaling criteria or dimensionless approaches are briefly summarized along with their applications in EOR. In addition, it reviews how scaling criteria can be derived using a mathematical model along with their benefits and shortcomings. This work concentrates on assessing the application of nanoparticles in EOR processes and addresses the process controlling parameters. This study briefly evaluates a few appropriate analytical and semi-analytical studies directly related to nanoparticle-assisted EOR techniques. Several nanoparticles assisted experimental works have been reviewed for both core flooding and micromodel systems. [ABSTRACT FROM AUTHOR]

The combined effects of gravitational forces and wettability on displacement and trapping have not previously been investigated experimentally in realistic 2D porous media. Here we report the first use of representative 2D micromodels that accurately reproduce characteristic geometric, morphological, and topological properties of 3D sand packs. We use these representative micromodels to compare the wettability dependence of displacement front morphology and trapping processes using selected fluid pairs at capillary numbers between 10−6 and 10−5. The contact angles studied ranged from 30° (normal imbibition) to 150° (strong drainage). The impact of gravity was dramatic: In the horizontal flow case, only one finger developed, that is longitudinal displacement was always favored, whereas gravity created a more compact displacement front with broad lateral extension, and this lateral movement created loops, leading to by‐pass trapping. As a result, the trapping efficiency rose from 7% to 29%. We observed universal scaling of the cluster size distribution demonstrating that our micromodels are statistically representative. The universal 2D‐scaling exponent of 2.05 was obtained with an acceptable error smaller than 5%. Our experimental results obtained by fluorescence microscopy showed (a) precursor corner flow for weak imbibition at θ = 51°, that is above the critical contact angle of αc = 45° (Zhao et al., 2016, https://doi.org/10.1073/pnas.1603387113), and (b) a new wetting transition from corner flow to full duct flow under neutral wettability conditions, that is at θc ≈ 90°; and (c) above this second critical contact angle, that is under strong drainage conditions, we again observed corner flow (specifically, core‐annular flow). Key Points: Micromodel‐study of the interplay between wettability, surface roughness and trapping efficiency using representative Si‐micromodelsComparison of the horizontal and vertical displacement process to investigate the combined effect of wettability and gravityStudy of precursor corner flow from normal imbibition (30°) to strong drainage (150°) [ABSTRACT FROM AUTHOR]

Resolving pore-scale transient flow dynamics is crucial to understanding the physics underlying multiphase flow in porous media and informing large-scale predictive models. Surface properties of the porous matrix play an important role in controlling such physics, yet interfacial mechanisms remain poorly understood, in part due to a lack of direct observations. This study reports on an experimental investigation of the pore-scale flow dynamics of liquid CO2 and water in two-dimensional (2D) circular porous micromodels with different surface characteristics employing high-speed microscopic particle image velocimetry (μPIV). The design of the micromodel minimized side boundary effects due to the limited size of the domain. The high-speed μPIV technique resolved the spatial and temporal dynamics of multiphase flow of CO2 and water under reservoir-relevant conditions, for both drainage and imbibition scenarios. When CO2 displaced water in a hydrophilic micromodel (i.e., drainage), unstable capillary fingering occurred and the pore flow was dominated by successive pore-scale burst events (i.e., Haines jumps). When the same experiment was repeated in a nearly neutral wetting micromodel (i.e., weak imbibition), flow instability and fluctuations were virtually eliminated, leading to a more compact displacement pattern. Energy balance analysis indicates that the conversion efficiency between surface energy and external work is less than 30%, and that kinetic energy is a disproportionately smaller contributor to the energy budget. This is true even during a Haines jump event, which induces velocities typically two orders of magnitude higher than the bulk velocity. These novel measurements further enabled direct observations of the meniscus displacement, revealing a significant alteration of the pore filling mechanisms during drainage and imbibition. While the former typically featured burst events, which often occur only at one of the several throats connecting a pore, the latter is typically dominated by a cooperative filling mechanism involving simultaneous invasion of a pore from multiple throats. This cooperative filling mechanism leads to merging of two interfaces and releases surface energy, causing instantaneous high-speed events that are similar, yet fundamentally different from, burst events. Finally, pore-scale velocity fields were statistically analyzed to provide a quantitative measure of the role of capillary effects in these pore flows.

Absract—: Approaches for the experimental and numerical study of the distinctive features of fluid flow through media with double porosity that are based on micromodels of porous media and microfluidic technologies are proposed. The optic microscopy and tracer flow visualization methods are used to study experimentally fluid flow through model media. The numerical approach is based on the three-dimensional boundary element method accelerated with the use of the fast multipole method on heterogeneous computational architectures. The effect of structure parameters of micromodels on the flow distribution between the domains with different porosities is studied. Variation in the longitudinal and transvers velocity components in small and large pore channels is considered as functions of their geometric parameters and volumetric flow rate. [ABSTRACT FROM AUTHOR]

Micromodel can provide valuable information to improve understanding of pore-scale transport phenomenon and can also be utilized to simulate the transport process at pore scale. This research aims to propose settlement option for quantification of suspended solids in micromodel. The micromodel is used to mimic the formation damage which occurs in reservoir formation that could simultaneously affect enhanced oil recovery. This is done by utilizing visual image interpretation through image analysis on micromodel chip. Following the quantification of suspended solids, the micromodel was injected with brine that eventually forms agglomeration. Images are taken from NIS-Element AR microscope automatically in RGB color profile and then made into grayscale and finally into binary modes. Since the micromodel is simulated in 2D form structure, the quantification method complemented with image analysis is focusing on the quantified area, µm2 region of interest categorized into 3 main groups of area B05, M45 and T50, respectively. This research will explore on segmentation and thresholding processes of the visual data acquired from micromodel experiment. An image-based computational algorithm is programmed in MATLAB Image Processing Toolbox and ImageJ; hence, suspended solids in porous media could be quantified from the visual image executed in micromodel. [ABSTRACT FROM AUTHOR]

• The sludge dewatering process was firstly visualized by CT and micromodel. • The sludge dewaterability improved during anaerobic ammonia oxidation. • The invalid connected pore in sludge deteriorated sludge dewaterability. The solid-liquid separation is an indispensable and primary link in the process of sludge treatment and disposal. The past research was focused primarily on the technique explorations of sludge dewatering and always disregarded the internal pore structure and water migration behavior in sludge. In this work, the real three-dimensional pore structure of sludge was obtained by Nano-CT. Based on this, a pore-scale heterogeneous sludge micromodel was firstly presented, and the water flooding experiment was carried out to visualize the water migration behavior. The results showed that the sludge structure transformed from sheet-like floc to microsphere particles, and then agglomerated into large globular granules during anaerobic ammonia oxidation. And the equivalent pore size increases from 342 μm to 617 μm, improving the sludge dewaterability characterized by capillary suction time (CST). The most significant implication of this work was revealing the critical role of invalid connected pore in sludge dewatering. Such pore was not contributed to fluid flow but the circulating vortex in it even induced energy dissipation, thus deteriorated the sludge dewaterability. This work may be helpful to understand the critical role of pore characteristic in water migration and shed light on the new dewatering techniques from the perspective of regulating sludge structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Capillary desaturation and CDC in fractured porous media were probed in a micromodel. • No trend was observed for the CDCs in fractured matrices under water-wet conditions. • A consistent trend was recognized for the CDCs in oil-wet fractured matrices. • Oil-bridging and high-rate-interruption trapping events increased residual saturation. • DDM resulted in higher residual saturation than that in CDM in oil-wet model. Establishing the capillary desaturation curve (CDC) in subsurface porous media is necessary for planning non-aqueous phase liquid (NAPL) cleanup and recovery projects. CDCs are well established in fractures and intact (unfractured) rocks, but poorly so in fractured porous media where many industrial applications reside. We constructed the CDC in fractured porous media and explored the displacement/trapping mechanisms impacting its behavior using a newly designed fractured micromodel. The micromodel consisted of four different matrix blocks, surrounded by a fracture network, to probe the effect of variable pore elements sizes. Waterflooding experiments into the oil-saturated model at different injection rates were performed to characterize the desaturation process and develop the CDC under water-wet (WW) and oil-wet (OW) conditions. Capillary number formulas under the two wettability states were systematically defined, incorporating the size of the pore elements as well as the oil viscosity. In the WW model, no distinguishable trend was noted for the CDC. Capillary suction displacement, indicated by negative pressure responses, was identified during the experiments conducted at low capillary numbers. Under OW conditions, a modified capillary-number expression was proposed to account for the respective locations of the viscous and capillary forces. The obtained CDCs exhibited uniform trends compared to those in the WW model. Oil bridges, correlated with a peak in the pressure signal, were observed within the fracture between adjacent matrices. The residual oil saturation increased in the matrix blocks located at the terminus of the formed bridges. In addition, the residual oil saturation increased in the matrix block with the largest throat size due to oil bypassing by the water phase invading from multiple locations of the fracture. Volumes of the residual oil clusters were found to depend on the matrix throat size, but not the pore size. Finally, desaturation under the discontinuous displacement mode, tested via an individual multi-rate experiment, resulted in lower brine invasion into the matrices compared to that during the continuous displacement mode. The insights gained from this study can be extended to various applications involving multiphase flow in fractured porous media. [ABSTRACT FROM AUTHOR]

Abstract The applications of nanotechnology in oilfields have attracted the attention of researchers to nanofluid injection as a novel approach for enhanced oil recovery. To better understand the prevailing mechanisms in such new displacement scenarios, micromodel experiments provide powerful tools to visually observe the way that nanoparticles may mobilize the trapped oil. In this work, the effect of silicon oxide nanoparticles on the alteration of wettability of glass micromodels was investigated in both experimental and numerical simulation approaches. The displacement experiments were performed on the original water-wet and imposed oil-wet (after aging in stearic acid/n-heptane solution) glass micromodels. The results of injection of nanofluids into the oil-saturated micromodels were then compared with those of the water injection scenarios. The flooding scenarios in the micromodels were also simulated numerically with the computational fluid dynamics (CFD) method. A good agreement between the experimental and simulation results was observed. An increase of 9% and 13% in the oil recovery was obtained by nanofluid flooding in experimental tests and CFD calculations, respectively.

Abstract Nanofluids and low-salinity water (LSW) flooding are two novel techniques for enhanced oil recovery. Despite some efforts on investigating benefits of each method, the pros and cons of their combined application need to be evaluated. This work sheds light on performance of LSW augmented with nanoparticles through examining wettability alteration and the amount of incremental oil recovery during the displacement process. To this end, nanofluids were prepared by dispersing silica nanoparticles (0.1 wt%, 0.25 wt%, 0.5 wt% and 0.75 wt%) in 2, 10, 20 and 100 times diluted samples of Persian Gulf seawater. Contact angle measurements revealed a crucial role of temperature, where no wettability alteration occurred up to 80 °C. Also, an optimum wettability state (with contact angle 22°) was detected with a 20 times diluted sample of seawater augmented with 0.25 wt% silica nanoparticles. Also, extreme dilution (herein 100 times) will be of no significance. Throughout micromodel flooding, it was found that in an oil-wet condition, a combination of silica nanoparticles dispersed in 20 times diluted brine had the highest displacement efficiency compared to silica nanofluids prepared with deionized water. Finally, by comparing oil recoveries in both water- and oil-wet micromodels, it was concluded that nanoparticles could enhance applicability of LSW via strengthening wettability alteration toward a favorable state and improving the sweep efficiency.

Abstract Oil extraction often accompanied with relatively large amounts of water production causes several environmental and mechanical problems, particularly in oil-fractured reservoirs. One way to alleviate this problem is to use gels as a blockage agent. In this study, several micromodels with different geometries of fractures including a simple fracture, step fracture, fracture with variable mouth and fracture with a tiny crack were prepared. The amount of oil recovery was measured from these micromodels in the presence or absence of gel. In situ and preformed particle gels (PPGs) were injected into the micromodels to compare their ability in blocking fractures and increasing oil recovery. The BaCl2·2H2O salt solution was used to swell PPGs. The amount of salt concentration was optimized so that PPGs had maximum ability to block fractures. Several PPG concentrations, 1000, 2000, and 3000 ppm, were examined to optimize the amount of PPGs, which have to be injected into the micromodels. Injection flow rate was optimized so that salt water could efficiently sweep the matrix structure. Results showed that both PPG and in situ gels have a considerable effect on decreasing water production and increasing oil extraction. However, PPGs were superior in comparison to in situ gels to increase oil recovery. It was found that increasing salt concentration decreases the swelling percentage of PPGs. The optimum amount of injection flow rate was found to be 0.1 mL/hr for all the prepared micromodels. The optimum concentration of PPGs was different for each micromodel.

Generating the desired solute concentration signal in micro-environments is vital to many applications ranging from micromixing to analyzing cellular response to a dynamic microenvironment. We propose a new modular design to generate targeted temporally varying concentration signals in microfluidic systems while minimizing perturbations to the flow field. The modularized design, here referred to as module-fluidics, similar in principle to interlocking toy bricks, is constructed from a combination of two building blocks and allows one to achieve versatility and flexibility in dynamically controlling input concentration. The building blocks are an oscillator and an integrator, and their combination enables the creation of controlled and complex concentration signals, with different user-defined time-scales. We show two basic connection patterns, in-series and in-parallel, to test the generation, integration, sampling and superposition of temporally-varying signals. All such signals can be fully characterized by analytic functions, in analogy with electric circuits, and allow one to perform design and optimization before fabrication. Such modularization offers a versatile and promising platform that allows one to create highly customizable time-dependent concentration inputs which can be targeted to the specific application of interest.

Micromodels are important for studying various pore-scale phenomena in hydrogeology. However, the fabrication of a custom micromodel involves complicated steps with cost-prohibitive equipment. The direct fabrication of micromodels with a 3D printer can accelerate the fabrication steps and reduce the cost. A stereolithography (SLA) 3D printer is one of the best options because it has sufficient printing performance for micromodel fabrication and is relatively inexpensive. However, it is not without drawbacks. In this report, we explored the capability of an SLA 3D printer for micromodel fabrication. Various parameters affecting the printing results, such as the effects of geometries, dimensions, printing axis configurations, printing thickness resolutions, and pattern thicknesses were investigated using microtomography for the first time. Eventually, the most optimal printing configuration was then also discussed. In the end, a complete micromodel was printed, assembled, and used for fluid displacement experiments. As a demonstration, viscous and capillary fingerings were successfully performed using this micromodel design.

Clear understanding of pore-scale mechanisms that control transport and retention of colloids in porous media at different physicochemical conditions is critical to improve design and efficient cleanup methodologies of filter beds. The objective of this work was to investigate the impact of hydrophobicity, solution ionic strength, and pH on colloid retention mechanisms in single-phase and two-phase flow in porous media systems. A series of experiments were conducted using a geometrically representative micromodel. Hydrophilic and hydrophobic colloids were dispersed in water at different solution ionic strength and pH conditions. Findings indicate that hydrophilic colloids exhibit high filtration efficiency as the colloids interact attractively with other colloids and solid-water-interface irrespective of the solution chemistry. However, for hydrophobic colloids, changes in solution chemistry significantly increase colloid retention where the colloid interaction become attractive with the increase in ionic strength and decrease in pH values. Colloids attached to the collector surfaces mobilized by the strong capillary forces induced by the moving gas-water interface and transported along with the interface. However, hydrophilic colloids redeposited on gas-water-solid interfaces or thin water films because of their greater capillary potential. Therefore, greater filtration efficiency is achieved with the hydrophilic colloids compared to the hydrophobic colloids for which the efficiency can be improved by changing the solution chemistry. Moreover, the removal efficiency by the moving gas-water interface was observed to be more for hydrophobic colloids compared to hydrophilic colloids for which the efficiency can be improved by lowering the ionic strength or increasing the pH value. This study indicates that the coupled effects of solution chemistry and colloid hydrophobicity should be taken into account while investigating efficient filtration and cleaning practices for the filter beds. Unlabelled Image • Applying a geometrically representative micromodel to study colloid retention mechanisms. • The filtration of hydrophobic colloids has been improved by altering solution chemistry. • Use of moving gas-water interface to clean filter beds with hydrophobic colloids. • Impact of solution chemistry differ for hydrophilic and hydrophobic colloids. • Incorporating coupled effects of ionic strength and pH on colloid transport mechanisms. [ABSTRACT FROM AUTHOR]

The process of fluid displacement in a microscale of porous media in oil reservoirs rock is affected by several factors. Understanding the effects of factors in multiphase flow mechanisms in porous media through numerical investigations allows us to estimate the flow behavior. In this study, the effect of important parameters like viscosity ratio and velocity on displacement in porous media was investigated using the volume of fluid method as a numerical model. So, a set of governing equations were calculated under a wide range of injection velocities and viscosity ratios to characterize displacing pattern. A similar experiment was done on a micromodel to validate the numerical method, and a rational agreement was reached between the experimental and numerical results. Saturation, velocity, pressure, breakthrough times, displacement efficiencies and displacement patterns were studied. Results show that the effect of viscosity ratio is more important than the effect of velocity. If the viscosity ratio increases five times, injection rate has to decrease 10 times to recover the same amount of oil. However, in a homogeneous porous media, fingering takes place due to the interaction of some forces where in a heavy oil reservoir the viscous forces play the main role. Also, pore scale events were investigated to better understanding the role of film rupture, coalescence, pinch off and splitting in meniscus displacement through the throat of the pore. [ABSTRACT FROM AUTHOR]

This research illustrates the effect of miscibility condition between nanofluid and oil on the process efficiency and to achieve this aim four types of fluid including distilled water, ethanol, n-hexane, and gas condensate were used to disperse silica nanoparticles. The prepared nanofluids were injected into a glass micromodel and the oil recovery factor and effective mechanisms were investigated. Results showed that in presence of nanoparticles, the oil recovery factor for miscible base fluids injection increases about 30%. But in immiscible base fluids, nanoparticles enhance the oil recovery factor up to 20% more than the base fluids. So nanoparticles are more efficient in miscible base fluids compared to immiscible ones.

Nano- and microparticles are expected to have several functionalities, and the ability to control size and shape is an advantage of using nano-/microparticles. This study investigated a possibility that the sizes of nano-/microparticle can be used to extract new information on structures in a fractured medium. Flow experiments were conducted to observe the particle transport in a micromodel on which a single fracture and rock matrix (grain and pore space) was fabricated on a silicon wafer. Water and nano-/microparticles were injected into the micromodel, and the droplets were collected at the outlet. Tunable Resistive Pulse Sensing (TRPS) was used to measure the frequency distributions of particle diameters from each droplet at each time. The result shows that the larger particles were observed only at early time, while the smaller particles were detected at early time and also at late time. This indicates that the larger particles flow in a fracture quickly, while smaller particles migrate through both fracture and matrix over a wider range of time. Particles with different sizes transport through fractured media differently depending on the fracture structures. The tracer response of nano- and microparticles may be useful to evaluate the fracture structures and the flow properties for different flow pathways. [ABSTRACT FROM AUTHOR]

Modeling coupled systems of free flow adjacent to a porous medium by means of fully resolved Navier–Stokes equations is limited by the immense computational cost and is thus only feasible for relatively small domains. Coupled, hybrid-dimensional models can be much more efficient by simplifying the porous domain, e.g., in terms of a pore-network model. In this work, we present a coupled pore-network/free-flow model taking into account pore-scale slip at the local interfaces between free flow and the pores. We consider two-dimensional and three-dimensional setups and show that our proposed slip condition can significantly increase the coupled model's accuracy: compared to fully resolved equidimensional numerical reference solutions, the normalized errors for velocity are reduced by a factor of more than five, depending on the flow configuration. A pore-scale slip parameter β pore required by the slip condition was determined numerically in a preprocessing step. We found a linear scaling behavior of β pore with the size of the interface pore body for three-dimensional and two-dimensional domains. The slip condition can thus be applied without incurring any run-time cost. In the last section of this work, we used the coupled model to recalculate a microfluidic experiment where we additionally exploited the flat structure of the micromodel which permits the use of a quasi-3D free-flow model. The extended coupled model is accurate and efficient. [ABSTRACT FROM AUTHOR]

In this study, the performance of biosurfactants produced by Enterobacter cloacae (PTCC:1798) and Acintobacter calcoaceticus (PTCC:1318) is investigated and the optimum values of operational parameters such as salinity%, MEOR type, and microorganism type to enhance the recovery from oil reservoirs are introduced. A comparison between ex-situ and in-situ injection in micromodel is also provided and the efficiency of produced biosurfactants in EOR is investigated for the first time in the literature. Experiments were designed using general factorial method in Design Expert software. In order to do that, design of experiment (DOE) followed by experimental flooding tests into a micromodel and response surface methodology (RSM) were employed. According to experimental design, four levels of salt concentration (0, 3%, 6%, and 12%), two levels of injection type (in-situ and ex-situ), and two levels of bacteria species were examined. The experiment results indicate a maximum oil recovery factor of 58% and 54% for in-situ injection obtained by Acintobacter at 3% salinity and Enterobacter at 6% salinity, respectively. The optimum oil recovery factors of 67% and 59% are achieved by ex-situ injection of water-biosurfactant from Acintobacter in CMC condition and 3% salinity and Enterobacter in CMC condition and 6% salinity, respectively. [ABSTRACT FROM AUTHOR]

The presence of nanoparticles (NPs), as new and efficient materials in enhanced oil recovery (EOR), has been considerably investigated in recent decades. In addition, smart surface modification of NPs is one of the capabilities recently defined in nanotechnology and nanoscience. Therefore, the main aim of this research is the application of new silica nanoparticles containing Al2O3 activators in EOR. Organosiloxane and amines have been used for surface modification and homogenized dispersibility of NPs in water-based as amine/organosiloxane@Al2O3/SiO2 (AOAS) nanocomposites synthesized using co-precipitation–hydrothermal method. These nanocomposites were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray methods (XRD), and dynamic light scattering (DLS). The stability of these nanocomposites was then investigated in different concentrations (100, 500, 1000, 2000 and 5000 ppm). Furthermore, contact angle, surface and interfacial tension have been measured. The results show that the surface modification process can significantly improve wettability and energetic surface activity. The use of AOAS nano-products in the specified concentrations for flooding into a micromodel shows that these nanocomposites can improve the oil efficiency. Besides, the oil recovery factors at 2000 ppm concentration for nanocomposites A, B (sequently were synthesized by impregnation and wet-chemical methods) and commercial nanosilica were found to be 66, 59.5 and 51.2%, respectively. It was observed that the new AOAS nanocomposites are able to improve the oil recovery factor of glass micromodel through the EOR process, compared with commercial silica nanoparticles. [ABSTRACT FROM AUTHOR]

Carbon nanofiller–modified polymers have been the subject of intense study for years due to their potential use in diverse and far-reaching applications. The effect of nanofiller network parameters on macroscale direct current electrical transport has been thoroughly elucidated by extensive nano-to-microscale modeling. As a result, we now have great insight into how the conductive and piezoresistive properties of nanocomposites can be tailored through judicious control of the underlying nanofiller network. It is also well-known that carbon nanofiller–modified polymers possess frequency-dependent alternating current electrical properties. Even though work has been done to understand the alternating current properties of nanocomposites via experimental characterization and through the development of macroscale equivalent circuit models, much less has been done to understand how macroscale alternating current conductivity depends on microscale effects such as nanofiller alignment and aspect ratio. This is an important knowledge gap because, like direct current conductivity, the underlying nanofiller network ultimately gives rise to macroscale alternating current transport in these materials. To this end, we herein present an alternating current microscale percolation model for carbon filler–based polymer nanocomposites. After calibration against experimental complex impedance data from randomly ordered carbon nanofiber–modified epoxy, this model is used to explore the effect of carbon nanofiber alignment and aspect ratio on alternating current conductivity. These simulations show that alternating current conductivity generally increases with increasing alignment and with aspect ratio; however, the competing effects of alternating current and direct current percolation give rise to substantial variation in alternating current conductivity at low frequencies and with poor percolation. The methodology presented in this article provides a modeling tool by which nanocomposites with highly optimized alternating current properties can be developed through careful control and tailoring of nanofiller network properties for the realization of exotic, next-generation material functionality. [ABSTRACT FROM AUTHOR]

This study focuses on the performance of nanosilica particles in the injected brine with different salt concentrations. For investigating the effect of SiO2-water-salt nanofluid in improving oil recovery, a set of experiment was conducted in both static and dynamic conditions. Interfacial Tension (IFT) measurement, contact angle measurements on glass surfaces, adhesion tests on sandstone grains and micromodel flooding tests were conducted. IFT results showed that although presence of nanoparticles can decrease the interfacial tension between injected brine and oil, but this change is not significant. The effect of nanofluid and salt concentration on the surface/fluid interaction was investigated by contact angle tests and new adhesion tests using grains of rocks. Both tests confirm that presence of nanofluid and salt can shift the wettability of rock surfaces towards more water wet condition. A glass micromodel was constructed for conducting flooding test to compare the capability of the nanofluid solution with/without salt, for improving oil recovery in dynamic conditions. The obtained results of all experiments demonstrated that silica nanoparticles are able to improve the wettability of both glass and sandstone surfaces towards more water-wet conditions. Wettability alteration by electrical double layer (EDL) and multicomponent ion exchange (MIE) are the dominant mechanisms in glass and sandstone surfaces during LSW injection and disjoining pressure is the major mechanism during nanofluid flooding. The presence of salts in the nanolfuids also showed to have a pronounced positive effect on the level of wettability alteration due to more adsorption of nanoparticles on the rock surface. [ABSTRACT FROM AUTHOR]

The remediation of nonaqueous phase liquids (NAPLs) enhanced by surfactant and nanoparticles (NP) has been investigated in numerous studies. However, the role of NP-assisted surfactants in the dissolution process is still not well discussed. Besides, there is a lack of empirical dissolution models considering the effects of initial residual saturation Strap, NAPL distribution, and surfactant concentration in NAPL-aqueous phase systems. In this work, micromodel experiments are conducted to quantify mass transfer coefficients for different injected aqueous phases including deionized water, SDS surfactant solutions, and NP-assisted solutions with different levels of concentrations and flow rates. Observations reveal that silica nanoparticles (SNP) can significantly enhance interphase mass transfer, while SDS surfactant reduces the mass transfer coefficient. In addition, Strap and intrinsic interfacial area ai, as an indicator of dense nonaqueous phase liquids (DNAPL) distribution, influence the interphase mass transfer. The ai is also independent of DNAPL saturation SNAPL except for SNAPL < 7% when ganglia breakup occurs. Based on these observations, new empirical dissolution models are proposed in the presence and the absence of SDS surfactant and SNP in which ai, Strap, and surfactant concentrations are introduced as new parameters. The evaluated mass transfer rate coefficients using the proposed models show a significant improvement compared to available empirical models. The finding of this study might be attractive for application in field-scale simulations of surfactant-enhanced aquifer remediation (SEAR) and NP-assisted methods. [ABSTRACT FROM AUTHOR]

Recently, nanoparticles have been used along with surfactants for enhancing oil recovery. Although the recent studies show that oil recovery is enhanced using nanoparticle/surfactant solutions, some effective parameters and mechanisms involved in the oil recovery have not yet been investigated. Therefore, the temperature effect on the stability of nanoparticle/surfactant solutions and ultimate oil recovery has been studied in this work, and the optimal concentrations of both SiO2 nanoparticle and surfactant (sodium dodecyl sulfate) have been determined by the Central Composite Design method. In addition, the simultaneous effects of parameters and their interactions have been investigated. Study of the stability of the injected solutions indicates that the nanoparticle concentration is the most important factor affecting the solution stability. The surfactant makes the solution more stable if used in appropriate concentrations below the CMC. According to the micromodel flooding results, the most effective factor for enhancing oil recovery is temperature compared to the nanoparticle and surfactant concentrations. Therefore, in floodings with higher porous medium temperature, the oil viscosity reduction is considerable, and more oil is recovered. In addition, the surfactant concentration plays a more effective role in reservoirs with higher temperatures. In other words, at a surfactant concentration of 250 ppm, the ultimate oil recovery is improved about 20% with a temperature increase of 20 °C. However, when the surfactant concentration is equal to 750 ppm, the temperature increase enhances the ultimate oil recovery by only about 7%. Finally, the nanoparticle and surfactant optimum concentrations determined by Design-Expert software were equal to 46 and 159 ppm, respectively. It is worthy to note that obtained results are validated by the confirmation test. [ABSTRACT FROM AUTHOR]

The interaction between fluid‐fluid and solid‐fluid interfacial forces and surface roughness controls the wettability. The ionic strength is the most important factor that controls electrostatic forces. Thus, a modification of the ionic strength can potentially lead to a change of the wettability, as shown in recent experimental works related to low‐salinity waterflooding, which is an enhanced oil recovery technology. Despite the significant research published on this topic, for the first time, we present how a change of the ionic strength alters the wettability in a pore network micromodel made of silanized polydimethylsiloxane (PDMS). We visualized the invasion of brine in an elongated hydrophobic PDMS micromodel, initially saturated with Fluorinert. Under different injection rates and ionic strengths and using image processing, we quantified the contact angle distribution in the flow network, the recovery curve with time, the brine breakthrough time, and the temporal change of resident saturation. The results imply that there is an optimal range of salinity at which saturation change accelerates and the breakthrough saturation maximizes, which highlights the concept of optimal salinity in wettability alteration. Also, we observed a shift of the contact angle distribution toward a more water‐wet state. Given the nonmonotonic trend of the breakthrough saturation with brine salinity, as well as recovery time versus the ionic strength, we conclude that the induced surface roughness is not the primary drive behind the accelerated saturation change. Therefore, the recovery time difference can be primarily attributed to the local alterations of the wetting properties of the porous medium due to the change of the ionic strength. Key Points: In the PDMS micromodel, reducing the ionic strength made the micromodel more water‐wetThere is an optimal range of salinity in which the dynamics of two‐phase flow through the porous medium accelerate, leading to faster recoveryThe total recovery in a PDMS micromodel can be attributed both to the wettability alteration, and the film flow through induced rough surfaces [ABSTRACT FROM AUTHOR]

[Display omitted] • Proposing CBLA as a remediation reagent for contaminated heterogeneous aquifers. • Pore-scale remediation simulation of organic pollutants with two-phase flow. • CBLA could improve the sweeping and extraction efficiency for PCE. • CBLA could improve the mobility and emulsification of PCE droplets. • The remediation efficiency of PCE was almost 100% at sandbox and micromodel scale. The heterogeneity of the aquifer seriously affects the remediation efficiency of dense non-aqueous phase liquid (DNAPL) due to the low contact efficiency for remediation reagents and DNAPL at macro scale and the restricted moving of DNAPL droplets by capillary forces in pore at micro scale. In this work, colloidal biliquid aphron (CBLA) as a remediation reagent was proposed, it has the rheological properties of shear thinning and the ultra-low interfacial tension between DNAPL. This work investigated the mechanisms and efficiencies of remediation DNAPL-contaminated heterogeneous aquifers using CBLA by sandbox and micromodel scale. The results indicated that CBLA could improve the mass transfer efficiency by both increasing the sweeping and extraction efficiency. The remediation efficiency of tetrachloroethylene (PCE) in aquifers with different permeability was above 99 % in sandbox, with the highest effluent concentration of 1.89 × 105 mg/L. Furthermore, at micromodel scale, CBLA could raise the remediation efficiency by improving the mobility and emulsification of PCE droplets. There was no PCE residue in the fine pore throats, and the remediation efficiency was 99.49 % in micromodel experiment and simulation. This work provided a promising remediation reagent for removing DNAPL from heterogeneous aquifers and laid a theoretical foundation for its practical application. [ABSTRACT FROM AUTHOR]

Microbial enhanced oil recovery (MEOR) is an economical method used to improve the oil recovery from reservoirs. In the MEOR techniques, by applying different microorganisms, a variety of products such as bioacid, biogas, biosurfactant, and biopolymer are generated, among which biosurfactant, one of the important metabolites, is produced by bacteria. It is worthy to note that bacteria are suitable candidates to enhance oil recovery due to their small size, rapid growth, capability of tolerating reservoir conditions, and production of different metabolites. Therefore, in this research, two bacteria, namely Enterobacter cloacae subsp with PTCC: 1798 isolated from oil-contaminated soil in south of Iran and Acinetobacter Calcoaceticus with PTCC: 1318, are used to produce biosurfactants. In order to evaluate the performance of generated biosurfactants, ex-situ flooding tests were performed in a glass micromodel to visualize the oil displacement and fluid front flow. In addition, water flooding is performed as a common EOR method for the better investigation of the produced biosurfactants. The results represented that injecting Enterobacter with a salinity concentration of 6% and Acinetobacter with a salinity concentration of 3% respectively increases the oil recovery factor by 27 and 35% compared to water flooding. In other words, the highest reduction in interfacial tension is achieved by the biosurfactant produced from Enterobacter and Acinetobacter at 6% and 3% salinity respectively, and the sequent changes in the interfacial tension are from 45 to 7 and 45 to 4 mN/m.

Fine-grained particles (fines) commonly coexist with coarse-grained sediments that host gas hydrate. These fines can be mobilized by liquid and gas flow during gas hydrate production. Once mobilized, fines can clog pore throats and reduce reservoir permeability. Even where particle sizes are smaller than pore-throat sizes, clogs can form due to clusters of fines. For certain types of fines, particularly swelling clays, cluster sizes depend on pore-fluid chemistry, which changes as pore-fluid freshens during gas hydrate dissociation. Fines can also be concentrated by a moving gas/liquid interface, increasing the chances of pore-throat clogging regardless of fines type. To test the relative significance of these clogging mechanisms, 2D micromodel experiments have been conducted with different pore-throat widths (20, 40, 60 and 100 μm), single-phase pore-fluids (deionized water and 2M-sodium-chloride solution), and moving gas/liquid interfaces on specimens from Sites NGHP-02-09 and NGHP-02-16 (NGHP-02: National Gas Hydrate Program Expedition 02) as well as a selection of pure fines (silica silt, mica, calcium carbonate, diatoms, kaolin, and bentonite). Clogging depended on the ratio of particle-to-pore throat size, and also on pore-fluid chemistry because the pore-fluid chemistry changes effectively increased or decreased the fine's cluster size relative to the pore-throat width. These interactions can be predicted based on the fine's electrical sensitivity (defined by Jang and Santamarina, 2016). The fine-grained sediment component (grain size < 75 μm) from the primary gas hydrate reservoir layers at Sites NGHP-02-09 and −16 show clogging via blocking or size exclusion (sieving) due to the large particles. Clogs also formed due to bridging or blocking by clusters of the smaller particles. Clogging generally occurred for pore-water sediment concentrations so low (0.2% by mass or less), that it was difficult to resolve the enhanced clogging in the presence of the gas/liquid meniscus. • Fines can be resuspended, migrate and clog pore throats as fluid and gas flows during gas hydrate dissociation. • Fines type determines if pore-fluid freshening from gas hydrate dissociation increases or decreases clustering and clogging. • Fines can be concentrated and localized by a moving gas/liquid interface, increasing the chances of pore-throat clogging. [ABSTRACT FROM AUTHOR]

Gas bubbles can be generated naturally or introduced artificially in porous media. Gas bubble migration through porous media governs the rate of gas emission to the atmosphere as well as the hydraulic and mechanical properties of sediments. The migration of air bubbles through water-wet porous media of uniform geometry was studied using a glass micromodel. Experiments were conducted to measure the velocity of bubbles of various lengths rising in a glass micromodel saturated with different test liquids and varying elevation angles. The results showed a linear dependency of the average bubble velocity on the bubble length and the sine of inclination angle of the micromodel. Comparisons were made using experimental data for air bubbles rising in kerosene, Soltrol 170 and dyed white oil. The effective permeability of the micromodel for the gas bubble, Kg, was calculated for different systems at different inclination angles, assuming that the effective length for viscous dissipation is equal to the initial static bubble length. It was found that the calculated permeability of the medium for gas bubbles had an increasing trend with increasing the bubble length. To visualize the periodic nature of the flow of rising bubbles in a porous medium, the motion of the air bubbles in white oil was video recorded by a digital camera, reviewed and analyzed using PowerDVDTM11 software. The bubble shape, exact positions of the bubble front and bubble tail during motion and, hence, the dynamic bubble length were determined through image analysis. Numerical simulation was performed by modifying an existing simulation code for the rise velocity of a gas bubble and the induced pressure field while it migrates through the pore network. The results showed that the rise velocity of a gas bubble is affected by the grid size of the pore network in the direction perpendicular to the bubble migration. The findings of this study can have important implications for studies on the migration of injected gas bubbles in geoenvironmental applications, as well as fundamental studies on bubble transport and behavior in porous media. [ABSTRACT FROM AUTHOR]

Oil extraction often accompanied with relatively large amounts of water production causes several environmental and mechanical problems, particularly in oil-fractured reservoirs. One way to alleviate this problem is to use gels as a blockage agent. In this study, several micromodels with different geometries of fractures including a simple fracture, step fracture, fracture with variable mouth and fracture with a tiny crack were prepared. The amount of oil recovery was measured from these micromodels in the presence or absence of gel. In situ and preformed particle gels (PPGs) were injected into the micromodels to compare their ability in blocking fractures and increasing oil recovery. The BaCl2·2H2O salt solution was used to swell PPGs. The amount of salt concentration was optimized so that PPGs had maximum ability to block fractures. Several PPG concentrations, 1000, 2000, and 3000 ppm, were examined to optimize the amount of PPGs, which have to be injected into the micromodels. Injection flow rate was optimized so that salt water could efficiently sweep the matrix structure. Results showed that both PPG and in situ gels have a considerable effect on decreasing water production and increasing oil extraction. However, PPGs were superior in comparison to in situ gels to increase oil recovery. It was found that increasing salt concentration decreases the swelling percentage of PPGs. The optimum amount of injection flow rate was found to be 0.1 mL/hr for all the prepared micromodels. The optimum concentration of PPGs was different for each micromodel. [ABSTRACT FROM AUTHOR]

The applications of nanotechnology in oilfields have attracted the attention of researchers to nanofluid injection as a novel approach for enhanced oil recovery. To better understand the prevailing mechanisms in such new displacement scenarios, micromodel experiments provide powerful tools to visually observe the way that nanoparticles may mobilize the trapped oil. In this work, the effect of silicon oxide nanoparticles on the alteration of wettability of glass micromodels was investigated in both experimental and numerical simulation approaches. The displacement experiments were performed on the original water-wet and imposed oil-wet (after aging in stearic acid/n-heptane solution) glass micromodels. The results of injection of nanofluids into the oil-saturated micromodels were then compared with those of the water injection scenarios. The flooding scenarios in the micromodels were also simulated numerically with the computational fluid dynamics (CFD) method. A good agreement between the experimental and simulation results was observed. An increase of 9% and 13% in the oil recovery was obtained by nanofluid flooding in experimental tests and CFD calculations, respectively. [ABSTRACT FROM AUTHOR]

One of the most effective methods of mitigating carbon dioxide emission is geological sequestration, in which an enormous amount of CO 2 captured from the main sources of CO 2 is injected into deep underground layers for long-term storage. The most capacious of these storage sites are saline aquifers. The capacity and safety of these storage sites are governed by capillary force. Among the parameters influencing capillary pressure, the wettability of rock, which is quantified by the contact angle, has the highest uncertainty. Measuring the contact angle in real conditions inside the pores of a rock is ideal, but technical issues force researchers to measure the contact angle of a bubble of CO 2 or a water/brine droplet on a flat surface, which cannot model the real fluid configuration inside the pores. In our experimental study, we used a transparent glass 2D micromodel with randomly patterned channels in order to inject CO 2 and brine with different salinities, then measured the contact angle of the water-CO 2 interface on glass channel wall surfaces. Our pore-scale dynamic contact angle results showed that by increasing the pressure from 1 to 8 MPa (equivalent to increasing the depth from 100 to 800 m, respectfully), the receding and advancing contact angles increased for all brines with different salinities (0.1, 1, and 3 molarity of NaCl). For example, the receding contact angle increased from ∼60° to ∼90° with the increased pressure for brine with 1M salinity. A higher contact angle, which indicates lower capillary pressure, increases the risk of the leakage through ground layers and the migration of CO 2 back to the surface. Moreover, increased salinity results in an increased contact angle for a specific pressure, which must be considered for the safety of any storage site. Also, contact angle hysteresis, which is an important parameter for immobilizing CO 2 bubbles inside of the rock pores, increases with pressure and decreases with salinity. • The receding and advancing contact angles increased for all brines with different salinities (0.1, 1, and 3 molarity of NaCl) by increasing the pressure from 1 to 8 MPa. • Increased salinity results in an increased contact angle for a specific pressure, which must be considered for the safety of any storage site. • Contact angle hysteresis, which is an important parameter for immobilizing CO 2 bubbles inside of the rock pores, increases with pressure and decreases with salinity. [ABSTRACT FROM AUTHOR]

Nanofluids and low-salinity water (LSW) flooding are two novel techniques for enhanced oil recovery. Despite some efforts on investigating benefits of each method, the pros and cons of their combined application need to be evaluated. This work sheds light on performance of LSW augmented with nanoparticles through examining wettability alteration and the amount of incremental oil recovery during the displacement process. To this end, nanofluids were prepared by dispersing silica nanoparticles (0.1 wt%, 0.25 wt%, 0.5 wt% and 0.75 wt%) in 2, 10, 20 and 100 times diluted samples of Persian Gulf seawater. Contact angle measurements revealed a crucial role of temperature, where no wettability alteration occurred up to 80 °C. Also, an optimum wettability state (with contact angle 22°) was detected with a 20 times diluted sample of seawater augmented with 0.25 wt% silica nanoparticles. Also, extreme dilution (herein 100 times) will be of no significance. Throughout micromodel flooding, it was found that in an oil-wet condition, a combination of silica nanoparticles dispersed in 20 times diluted brine had the highest displacement efficiency compared to silica nanofluids prepared with deionized water. Finally, by comparing oil recoveries in both water- and oil-wet micromodels, it was concluded that nanoparticles could enhance applicability of LSW via strengthening wettability alteration toward a favorable state and improving the sweep efficiency. [ABSTRACT FROM AUTHOR]

Abstract Swelling and displacement of clay minerals during drilling and production of oil and gas reservoirs are among the main mechanisms of formation damage. Most reservoirs contain clay minerals, either originally deposited during sedimentation phase, or precipitated from fluids flowing through matrix. Owing to the large specific surface area of clay particles, their swelling, detachment, and migrationmay lead to permeability impairment in porous media. Therefore, an accurate interpretation of the behaviour of clay particles in the porous media may enable us to prevent and possibly reverse the respective damage mechanisms. In this work, the pore-scale swelling behaviour of clays are studied using glass micro models as porous medium and Sodium bentonite as swelling clay. By image processing technique, effective porosity of model during low salinity water (LSW) flooding are estimated. The effect of different parameters such as porous medium aspect ratio and clay concentration on permeability impairment is studied. According to this study, besides higher clay concentrations, the permeability is also affected adversely by larger aspect ratio of pore bodies. Based on our experiments, a model is developed to estimate permeability impairment by clay swelling as a function of pore geometry and clay concentration. Highlights • A micromodel setup is used for investigating the swelling behavior of Sodium bentonite during low salinity water flooding. • The effect of porous media aspect ratio and clay concentration on permeability impairment is studied. • A model is presented to estimate permeability change by clay swelling as a function of pore geometry and clay concentration. [ABSTRACT FROM AUTHOR]

Highlights • Low IFT was the main oil recovery mechanism for gravity driven imbibition. • With negligible gravity, solubilized oil diffused out of micromodel in a month. • Wettability alteration was not clearly identified as a mechanism for oil recovery. • Transverse viscous pressure gradients recovered oil in displacement experiments. Abstract Recovery in carbonate reservoirs is challenging because they are often oil wet and highly fractured. Surfactant flooding has been proposed as a possible enhanced oil recovery method to address these problems. To better understand the mechanisms of oil recovery from oil-wet, fractured rocks using surfactants, we created oil-wet glass micromodels, traversed by a deep fracture (130 µm) and conducted surfactant spontaneous imbibition experiments and floods at typical reservoir flow rates (approximately 2 ft/day). We compared the effects of capillary, viscous, and gravity forces as well as wettability alteration. We show, by conducting spontaneous imbibition experiments with negligible gravity effects (inverse Bond number ∼105) and by analyzing the results using simple force balance calculations, that in our micromodels low IFT plays the key role in balancing the viscous, gravity, and surface forces and hence the dynamics of imbibition. To quantify the role of viscous forces, we present displacement experiments at low IFT (10−3 mN/m) where transverse viscous pressure gradients mobilize oil from the matrix into the fracture. These results help rationalize and quantify the contributions of gravity, wettability alteration, and viscous crossflow to the rate of matrix-fracture transfer at low-IFT conditions. [ABSTRACT FROM AUTHOR]

Abstract Nanofluid injection has emerged as an attractive enhanced oil recovery (EOR) process in the past decade. These fluids improve oil recovery by reducing interfacial tension (IFT), modifying wettability, and reducing mobility ratio. In this communication, magnetite citric acid-coated nanoparticles (NPs) were synthesized by an affordable, facile and one step method and then characterized using Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Dynamic light scattering (DLS). Afterward, the microscopic and macroscopic efficiencies of oil recovery in heterogeneous and homogeneous 2D micromodels were investigated in the presence of magnetic field. Citric acid-coated magnetite NPs started to respond to the magnetic field around the intensity of 800 Gauss and also showed the maximum ultimate recovery factor at the intensity of 2750 Gauss. In addition, citric acid coated magnetite NPs provided more enhanced oil recovery factor compared to hematite NPs, because of reducing interfacial tension (IFT) between the oil and injection fluid, altering surface wettability from oil-wet to water-wet, promoting the NPs distribution in porous media, and generating column-like structure in the presence of magnetic field. In fact, magnetite NPs act as piston toward the magnetic field by creating a column which sweeps the oil and increases production. Furthermore, citric acid-coated magnetite NPs flooding increased ultimate recovery factor more than polymer and hematite NPs flooding. Graphical abstract Image 1 Highlights • Magnetite citric acid-coated nanoparticles (NPs) were synthesized by an affordable, facile and one step method. • The microscopic and macroscopic efficiency of oil recovery were investigated in the presence of magnetic field. • Magnetite NPs act as piston toward the magnetic field by creating a column which sweeps the oil. • Citric acid-coated magnetite NPs flooding increased ultimate recovery factor more than polymer and hematite NPs flooding. [ABSTRACT FROM AUTHOR]

Abstract The present study simulated thermal enhanced oil recovery (steam and nanoparticles) for the first time using computational fluid dynamics. To better visualize fluid flow in the reservoir, a 2D micromodel generated by commercial grid generation tools was used as the porous medium. Four parameters that have a great impaction on the process were studied to determine the best combination of factors to attain maximum oil recovery. Type of nanoparticle, volume fraction of nanoparticles, diameter of nanoparticles and temperature of injected fluid were examined using the Taguchi method. All governing equations were solved in Fluent software based on finite volume. The numerical results were in a good agreement with the experimental results and the data shows that Al 2 O 3 nanoparticles have the greatest potential for enhanced oil recovery in comparison with CuO and Fe 3 O 4 nanoparticles. Decreasing the diameter of the nanoparticles and increasing their volume fraction in the base fluid and the temperature of the injected fluid improved oil recovery and a large amount of oil was produced from the porous medium. Injecting the nanofluid at an optimal level decreased the viscosity of the extra heavy oil from 35 to 25 Pa s. Highlights • CFD simulation of a thermal enhanced oil recovery process in a 2D micromodel for first time. • Investigation of effective parameters on the oil recovery factor using Taguchi. • Finding that Al 2 O 3 nanoparticles have a great potential in enhanced oil recovery processes in comparison with CuO and Fe 3 O 4 nanoparticles. • Studying viscosity reduction of crude oil during the optimal test and finding that by injecting the nanofluid at an optimal level, viscosity of extra heavy oil decreases from 35 Pa s to 25 Pa s. [ABSTRACT FROM AUTHOR]

Abstract Chemical-assisted waterflooding enhances the ultimate recovery of a conventional waterflooding process through several mechanisms such as reducing interfacial tension between water and oil, formation of in-situ emulsions, treatment of adverse mobility ratio, and wettability modification. Application of chemical-assisted waterflooding for recovery of heavy oil is still an active research topic. A new chemical technology (i.e. IPC Technology as referred to in this paper) has been developed. A proprietary mixture of surfactants is used in several techniques associated with surface extraction as well as in-situ recovery of heavy oil and bitumen. This formulation of solvents and surfactants is reusable, low foaming, non-flammable, not acutely toxic, and non-carcinogenic. The efficacy of using IPC as an additive for waterflooding was presented earlier through a systematic coreflooding study, which showed increased ultimate recovery of different types of oils when compared with commercial surfactant and alkali flooding. In order to investigate the mechanisms behind the enhanced macro-scale oil recovery, a series of pore-scale tests were designed and conducted in this study. Glass micromodel type of porous media was used in the presence of brines with different ion compositions. The pore-scale chemical-assisted waterflooding tests were carried out in four consecutive stages: brine flooding, chemical flooding, soaking period, and extended brine flooding. High quality pore-scale images were captured for qualitative and quantitative analysis of the IPC-assisted waterflooding at the pore-level. IPC intensified water wettability of grain particles in the presence of NaCl; however in the presence of MgCl 2 , use of IPC makes solid surfaces oil-wet. The phenomenon of water-in-oil and oil-in-water emulsification was observed when IPC was used along with different brine compositions. This phenomenon is weakened for lighter oils. When the acid number of the oil was low, extension of soaking period intensified wettability alteration and emulsification mechanisms. Other pore-scale phenomena were also observed during visualization tests such as coalescence of microdroplets during the extended waterflooding stage, snap-off mechanism creating daughter droplets during the extended waterflooding stage, occasional flow of bulk oil films toward the production end, and wettability reversal during various flooding stages. Attempts were also made to conduct statistical analysis of emulsion droplet sizes under different test conditions. Several parameters, including chemical concentration as well as ion concentration in brines, were found to significantly affect the emulsion droplet size distribution. [ABSTRACT FROM AUTHOR]