Permeability Oil Research Articles

The Effect of Wettability and Flow Rate on Oil Displacement Using Polymer-Coated Silica Nanoparticles: A Microfluidic Study

Polymer-coated silica nanoparticles (PSiNPs) have been experimentally investigated in core- and micro-scale studies for enhanced oil recovery (EOR). Wettability and flow rate have a considerable effect on oil displacement in porous media. This work investigates the efficiency of PSiNPs for oil recovery on micro-scale at three wettability states (water-wet, intermediate-wet, and oil-wet). In addition, a cluster mobilization regime is considered in all experiments. A microfluidic approach was utilized to perform flooding experiments with constant experimental settings such as flowrate, pore-structure, initial oil topology, porosity, and permeability. In this study, the wettability of the microfluidic chips was altered to have three states of wettability. Firstly, a micro-scale study (brine-oil-glass system) of each wettability condition effect on flow behavior was conducted via monitoring dynamic changes in the oleic phase. Secondly, the obtained results were used as a basis to understand the changes induced by the PSiNPs while flooding at the same conditions. The experimental data were extracted by means of image processing and analysis at a high spatial and temporal resolution. Low injection rate experiments (corresponding to ~1.26 m/day in reservoir) in a brine-oil-glass system showed that the waterflood invaded with a more stable front with a slower displacement velocity in the water-wet state compared to the other states, which had water channeling through the big pores. As a result, a faster stop of the dynamic changes for the intermediate- and oil-wet state was observed, leading to lower oil recoveries compared to the water-wet state. In a cluster mobilization regime, dynamic changes were noticeable only for the oil-wet condition. For the aforementioned different conditions, PSiNPs improved oil displacement efficiency. The usage of PSiNPs showed a better clusterization efficiency, leading to a higher mobilization, smaller remaining oil clusters, and lower connectivity of the residual oil. The knowledge from this experimental work adds to the understanding of the behavior of polymer-coated silica nanoparticles as a recovery agent at different wettability states and a cluster mobilization regime.

Durable CNTs Reinforced Porous Electrospun Superhydrophobic Membrane for Efficient Gravity Driven Oil/Water Separation

Developing a durable and efficient oil/water separation membrane for purification of the oily water is crucial for sustainable aquatic ecosystems and public health. Herein, a superhydrophobic and superoleophilic nanofibrous membrane was successfully developed with an improved mechanical strength via a facile method of blend-electrospun. By introducing an ultralow amounts of carbon nanotubes (CNTs, 0.15 wt%, 2.55 mg/g), the obtained composite membrane exhibited a satisfactory hydrophobic (water contact angle, WCA = 152°) and oleophilic nature (oil contact angle, OCA ∼ 0°, oil permeation time =91.63 ms). The as-prepared composite membrane exhibited a strong acid/alkali resistance (pH = 1–14), high thermal stability (160 °C), and good mechanical stability; it had a high oil-water separation flux (max = 9270 L m-2 h-1) and a separation efficiency of > 99% under the driving of gravity, indicating a significant applicability for energy-saving filtration. The integration of high performance, low cost, and a simple solution-based fabrication process makes the as-prepared membranes have a great potential for future applications.

Expanded Polytetrafluoroethylene/Graphite Composites for Easy Water/Oil Separation.

Oil spills in the ocean greatly threaten local environments, marine creatures, and coastal economies. An automatic water/oil separation material system was proposed in this study, and a tubular geometry was chosen to demonstrate the water/oil separation efficiency and effectiveness. The water/oil separation tubes were made of expanded polytetrafluoroethylene (ePTFE) and graphite composites. The permeation pressures of water and oil through the tube walls were tuned by adjusting the ePTFE microstructure, which, in turn, depended on the degree of expansion and the graphite content. Fourier-transform infrared spectroscopy was performed to confirm the compositions of the ePTFE/graphite composites, and a scanning electron microscope was used to examine the microstructure and morphology of the expanded PTFE/graphite composite tubes. When a proper pressure was applied, which was higher than the oil's permeation pressure (3.0 kPa) but lower than the water's permeation pressure (57 kPa), the oil leaked out of the tube walls while the water went through the ePTFE/graphite tubes. As such, the water/oil mixture could be separated and collected in different containers or an outer tube. Due to this automatic separation, the whole process could be done continuously and conveniently, thus exhibiting great potential in the practical applications of oil spill and water separation/remediation.

The research status and summary of adsorption and retention mechanism of polymer

The polymer flooding technology has been established a relatively scientific and complete technical theory system, after decades of development. Theoretical and field applications have shown that the key to profile control and flooding is adsorption and retention of polymer in reservoirs. When the polymer flows through the porous medium of the reservoir, it will be adsorbed and trapped in the pores of the cores, resulting in serious decrease in the permeability of water in the porous medium of the reservoir, while only a slight decrease in the permeability of oil, increasing the mobility of crude oil, effectively increasing the injected water swept volume, and thereby improving the comprehensive economic benefit of water-flooding development reservoir. In order to further understand the adsorption and retention mechanism of polymer, guide the oilfield production, and achieve the purpose of low injection of polymer and the high production of oil, in this paper, we conducted a lot of research on the adsorption and retention mechanism of polymer at home and abroad. The comprehensive analysis shows that electrostatic and mechanical trapping are the main causes of adsorption and retention, followed by polymer concentration, degree of hydrolysis, rock wettability and formation mineralized water composition.

Application of Implicit Pressure-Explicit Saturation Method to Predict Filtrated Mud Saturation Impact on the Hydrocarbon Reservoirs Formation Damage

Hydrocarbon reservoirs’ formation damage is one of the essential issues in petroleum industries that is caused by drilling and production operations and completion procedures. Ineffective implementation of drilling fluid during the drilling operations led to large volumes of filtrated mud penetrating into the reservoir formation. Therefore, pore throats and spaces would be filled, and hydrocarbon mobilization reduced due to the porosity and permeability reduction. In this paper, a developed model was proposed to predict the filtrated mud saturation impact on the formation damage. First, the physics of the fluids were examined, and the governing equations were defined by the combination of general mass transfer equations. The drilling mud penetration in the core on the one direction and the removal of oil from the core, in the other direction, requires the simultaneous dissolution of water and oil flow. As both fluids enter and exit from the same core, it is necessary to derive the equations of drilling mud and oil flow in a one-dimensional process. Finally, due to the complexity of mass balance and fluid flow equations in porous media, the implicit pressure-explicit saturation method was used to solve the equations simultaneously. Four crucial parameters of oil viscosity, water saturation, permeability, and porosity were sensitivity-analyzed in this model to predict the filtrated mud saturation. According to the results of the sensitivity analysis for the crucial parameters, at a lower porosity (porosity = 0.2), permeability (permeability = 2 mD), and water saturation (saturation = 0.1), the filtrated mud saturation had decreased. This resulted in the lower capillary forces, which were induced to penetrate the drilling fluid to the formation. Therefore, formation damage reduced at lower porosity, permeability and water saturation. Furthermore, at higher oil viscosities, due to the increased mobilization of oil through the porous media, filtrated mud saturation penetration through the core length would be increased slightly. Consequently, at the oil viscosity of 3 cP, the decrease rate of filtrated mud saturation is slower than other oil viscosities which indicated increased invasion of filtrated mud into the formation.

A New Method of Predicting the Distribution of Remaining Oil by the Composite Index of Heterogeneity

As the Xingbei Development Zone gradually goes into the extra high water cut stage, the difficulty of residual oil tapping is becoming harder and harder. Heterogeneity not only controls the injection agent’s sweep coefficient, but also controls the injection displacement efficiency, which is the key factor affecting the formation and distribution of residual oil.Characterization of reservoir macroscopic heterogeneity by parameters such as sedimentary microfacies, oil layer structure, permeability, porosity and net thickness ratio. The heterogeneous comprehensive index obtained by the wave superposition method can not only quantitatively evaluate reservoir heterogeneity, but also explain the distribution characteristics of the residual oil.Using this method to fit the eastern part of a district of Xingbei Oilfield, The obtained heterogeneous composite index (IRH) distribution map is compared with the reservoir numerical simulation residual oil saturation map, and the correlation between the two is good. Statistically fit the production of new wells in the simulated area, wells with heterogeneous composite index between 0.55 and 0.75 have higher cumulative oil production, average daily oil production, and the water content is 2-5 percent lower than the average. According to the comprehensive analysis, the remaining oil enrichment area is in the IRH [0.55, 0.75] region. Guided by this method, we repart Well B1; let free its S II 8 accompanying water blocking layer, so as to strengthen liquid supply to Well B2 and Well B3, which are rich in residual oil through this method. The production plan proves to be effective, Well B2’s daily oil production increases by 1.5t, and Well B3’s daily oil production increases by 1.2t. Till now, the accumulated increasing oil production has up to 1324t, which equals to economic benefits of 3840,000 RMB.Through quantitative characterization of reservoir heterogeneity, we find that the remaining oil enrichment zone is mostly located in the IRH [0.55, 0.75] region, which has important guiding significance for the future development.

Experimental studies on reaction laws during the process of air injection into the oil reservoirs with low permeability

The low permeability oil reservoirs are widely distributed in the world, but difficult to develop with the traditional methods due to the low permeability and poor injection properties. Air injection technique not only has the common characteristics of other gas injection techniques, but also can improve the quality of crude oil in situ because of the oxidative ability of the injected air, with a unique advantage in developing low permeability reservoirs. In order to study the reaction regularity between the hydrocarbon components in crude oil under different conditions with the oxygen in the injected air, this experiment is designed for a low permeability sandstone reservoir. In this experiment, one set of self-designed static low-temperature oxidation equipment (including injection pump and high-temperature high–pressure reactor with sampling outlets) has been used. Through analysis of the results of the chromatography for over 60 oil and gas samples, conclusions can be made that after low temperature oxidation (LTO) reactions between the crude oil and the oxygen in the injected air, the concentration of the heavy components in crude oil decreased, and the concentration of the light components increased. By injecting oxygen-reduced air with 8% of oxygen, the concentration of the heavy components of crude oil in the target reservoir reduced most obviously. The formation water and associated gas can hinder the pyrolysis of heavy components, while the minerals in the formation can accelerate the pyrolysis process. The relationship between the carbon atoms number in each of the most consumed hydrocarbon molecule and different LTO reaction conditions has been proposed. According to the sensitivity analysis, it is believed that the influence of the formation water on the LTO reactions is greater than that of minerals in the formation, and influence of associated gas is less than that of minerals. Finally, combined the related physical and chemical theories, a LTO chemical reaction equation has been put forward for the targeted low permeability oil reservoir. The conclusions of the studies can provide some references for the indoor experiments and field applications of air injection in the future.

Petrographical characteristics and post-depositional alteration affecting porosity and permeability of Oligocene sandstones, block 15-1/05, Cuu Long basin

Petrographical characteristics and post-depositional alteration studies of sandstones are the two important factors to reservoir rocks, which affect oil and gas storage and permeability of reservoir rocks. This study revealed petrographical characteristics, post-depositional alteration, and their influence on the porosity and permeability of Oligocene sandstones, including C, D, and E and F sequences, block 15-1/05, Cuu Long Basin. The results show that most of the sandstones were arkose, lithic arkose, and sporadically interbedded by feldspathic greywacke. The post-depositional alteration was progressively increasing following the burial depth from early diagenesis of sequence C, to intermediate diagenesis of sequence D and advanced diagenesis of sequence E and F. The post-depositional alterations significantly influenced on the porosity of the Oligocene sandstone were the cementation and mechanical compaction. They reduced the porosity and permeability of the sandstone. Additionally, authigenic clay minerals have a negative effect on permeability in which sandstones were rich illite and illite-smectite clay minerals, and the permeability tended to decrease stronger than others. Our results showed that the potential reservoir rocks of Oligocene sandstones, block 15-1/05 were sequence E and F sandstones that are in well grain sorting, well grain roundness shape, and contained a small number of cement, particularly the absence of illite and illite-smectite.

Bactericidal Lubricating Synthetic Materials for Three-Dimensional Additive Assembly with Controlled Mechanical Properties.

3D printable synthetic materials have been developed to realize desired surface and mechanical properties. Lubricating synthetic surfaces have broad technological impacts on many applications including food packaging, microfluidic systems, and biomedical devices. However, combining soft materials with lubricants leads to significant phase separation and swelling phenomena, together with lowered mechanical strength, impeding full utilization of lubricating synthetic surfaces with desired shapes in a highly controllable manner. Here, we report a new platform to create a 3D printable lubricant-polymer composite (3D-LUBRIC) for the seamless fabrication of multidimensional structures with diverse functionalities. The rationally designed lubricant-polymer mixtures including silica aerogel particles not only exhibit suitable rheological properties for direct ink writing without phase separation but also enable the deterministic additive assembly of heterogeneous materials, which have large mismatches of oil permeability, with no distinct shape distortion. While exhibiting excellent lubricating properties for a variety of liquids, 3D-LUBRIC shows tunable mechanical properties with desired functionalities, such as optical transparency, flexibility and stretchability, and anti-icing and antibacterial/bactericidal properties. We employ the proposed platform to fabricate self-cleanable containers and antibacterial/bactericidal medical tubes. Our platform can offer new opportunities for building low-adhesive, multifunctional synthetic materials with customized shapes for diverse applications.

A COMPREHENSIVE MODEL FOR OIL–WATER RELATIVE PERMEABILITIES IN LOW-PERMEABILITY RESERVOIRS BY FRACTAL THEORY

Oil–water relative permeability curve is an important parameter for analyzing the characters of oil and water seepages in low-permeability reservoirs. The fluid flow in low-permeability reservoirs exhibits distinct nonlinear seepage characteristics with starting pressure gradient. However, the existing theoretical model of oil–water relative permeability only considered few nonlinear seepage characteristics such as capillary pressure and fluid properties. Studying the influences of reservoir pore structures, capillary pressure, driving pressure and boundary layer effect on the morphology of relative permeability curves is of great significance for understanding the seepage properties of low-permeability reservoirs. Based on the fractal theory for porous media, an analytically comprehensive model for the relative permeabilities of oil and water in a low-permeability reservoir is established in this work. The analytical model for oil–water relative permeabilities obtained in this paper is found to be a function of water saturation, fractal dimension for pores, fractal dimension for tortuosity of capillaries, driving pressure gradient and capillary pressure between oil and water phases as well as boundary layer thickness. The present results show that the relative permeabilities of oil and water decrease with the increase of the fractal dimension for tortuosity, whereas the relative permeabilities of oil and water increase with the increase of pore fractal dimension. The nonlinear properties of low-permeability reservoirs have the prominent significances on the relative permeability of the oil phase. With the increase of the seepage resistance coefficient, the relative permeability of oil phase decreases. The proposed theoretical model has been verified by experimental data on oil–water relative permeability and compared with other conventional oil–water relative permeability models. The present results verify the reliability of the oil–water relative permeability model established in this paper.

Uncertainty quantification and sensitivity analysis for relative permeability models of two-phase flow in porous media

Computer simulations are usually employed for the prediction of oil reservoir performance under different extraction scenarios. Computational model parameters are adjusted to petrophysical properties of the reservoir and production data to forecast production profiles. However, some key features of these models, such as relative permeabilities of water and oil, are difficult to measure experimentally. As a consequence they can be considered a source of uncertainties, affecting the reliability of predictions. This work presents a study of uncertainty quantification and sensitivity analysis of different relative permeability models to assess the effects of input uncertainty on quantities of interest computed from a model of two-phase flow of water and oil. To explore different wettability regimes two different datasets were used, and two permeability models were employed. The probability distributions of parameters were estimated via the Markov Chain Monte Carlo method. Uncertainty propagation and sensitivity analyses were performed using the polynomial chaos expansion. The paper highlights output quantities that were most impacted by uncertain input data, and also the parameters which most contribute to the output variances.

Experimental study on the formation damage caused by gas fracturing fluids

Fracturing often results in a fluid invasion into the formation because the fracturing pressure is always greater than the reservoir pressure. The invaded fluid causes formation damage, oil permeability reduction, and potentially reduces production rates. We conduct experiments by invading gas into oil-saturated cores and vary the properties of the oil. We quantify the formation damage through pressure and saturation measurements. In addition, we model the experiment with a compositional fractional flow model, and the results show the formation damage caused by gas is cleared through dissolution transport. The results suggest that the time to clear depends on the fluid properties and the production rate.

An evaluation method of volume fracturing effects for vertical wells in low permeability reservoirs

To evaluate the fracturing effect and dynamic change process after volume fracturing with vertical wells in low permeability oil reservoirs, an oil-water two-phase flow model and a well model are built. On this basis, an evaluation method of fracturing effect based on production data and fracturing fluid backflow data is established, and the method is used to analyze some field cases. The vicinity area of main fracture after fracturing is divided into different stimulated regions. The permeability and area of different regions are used to characterize the stimulation strength and scale of the fracture network. The conductivity of stimulated region is defined as the product of the permeability and area of the stimulated region. Through parameter sensitivity analysis, it is found that half-length of the fracture and the permeability of the core area mainly affect the flow law near the well, that is, the early stage of production; while matrix permeability mainly affects the flow law at the far end of the fracture. Taking a typical old well in Changqing Oilfield as an example, the fracturing effect and its changes after two rounds of volume fracturing in this well are evaluated. It is found that with the increase of production time after the first volume fracturing, the permeability and conductivity of stimulated area gradually decreased, and the fracturing effect gradually decreased until disappeared; after the second volume fracturing, the permeability and conductivity of stimulated area increased significantly again.

Water sensitivity evaluation of sandstone oil reservoirs with ultra-low permeability

The development of sandstone reservoirs with ultra-low permeability has become one of the most important energy resources worldwide. Such reservoirs suffer formation damage easily, such as water sensitivity, from foreign fluid during well drilling and completion for extremely poor physical properties. In order to deeply understand the damage degree of water sensitivity of there reservoirs, water sensitivity analysis of Chang 6 reservoir rock samples was carried out, including water sensitivity of block matrix and fracture rock samples. Results show that there are none or weak water sensitivity damage for block matrix while medium water sensitivity damage for fractured samples. The study is of significance to the reservoir damage control in ultra-low permeability oil reservoirs.

Experimental Investigation of Anisotropic Thermal Deformation of Oil Shale Under High Temperature and Triaxial Stress Based on Mineral and Micro-fracture Characteristics

The anisotropic deformation of oil shale at different temperatures should be given particular attention considering that thermal deformation affects borehole stability, oil and gas permeation channel formation and surface subsidence during the pyrolysis of oil shale. The deformation of oil shale parallel and perpendicular to the bedding directions under different triaxial stresses was studied from room temperature to 600 °C. Evolutions in mineral compositions and thermal fracturing were studied by X-ray diffractometry and computer tomography, respectively. The main results are as follows. (1) Under 2.5 and 5 MPa axial stresses, the thermal deformation perpendicular to the bedding direction shows compressive deformation with increasing temperature, and the strain rate increases sharply at 200 °C, 350 °C and 400 °C. When the axial stress is 10 MPa, the deformation rate increases sharply when the temperature increases to 100 °C, and then, the compression deformation increases almost linearly. (2) Under 2.5 and 5 MPa axial stresses, the thermal deformation parallel to the bedding tends to be expansion–compression–expansion–recompression with increasing temperature. When the axial stress increases to 10 MPa, the overall deformation of the material will be compression deformation, and no expansion deformation will occur with the increase in temperature. (3) The deformation characteristics under the coupled action of temperature and stress are less related to mineral changes but more related to fracture evolution characteristics. (4) Thermal stress has a great influence on the thermal deformation of oil shale perpendicular to the bedding directions but little effect on the thermal deformation parallel to the bedding directions.

Production of a bacterial cellulose/poly(3-hydroxybutyrate) blend activated with clove essential oil for food packaging

The aim of the present study was to produce a blend of bacterial cellulose (BC) and poly(3-hydroxybutyrate) (PHB) from the combination of pure BC membranes and 30% PHB in acetic acid. Clove essential oil (CLO) was then added as an antimicrobial agent. BC membranes were produced from Gluconacetobacter hansenii in a modified Hestrin–Schramm medium containing corn steep liquor. The scanning electron microscopic analyses revealed a visible white lining on the BC surface due to the deposition of PHB. Other analyses such as oil permeability, flexibility, and water solubility, which showed no trace of oil permeation through the films, resistance to folding (more than 100 times), and hydrophobicity, respectively, demonstrated the improvement of the material due to the blend of the polymers. When compared with the pure PHB polymer membrane, the addition of the essential oil led to a substantial reduction of 65% in microbial growth and better mechanical and thermal properties, since the traction resistance value increased by 3.9 times while the maximum degradation rate was 10°C higher. The new material, composed of BC/PHB with the addition of CLO, has attractive properties for use as a biocompatible, biodegradable, active food packaging wrap.

Surfactant-dependent critical interfacial tension in silicon carbide membranes for produced water treatment

During fossil oil extraction, a complex water stream known as produced water (PW), is co-extracted. Membrane treatment makes PW re-use possible, but fouling and oil permeation remain major challenges. In this work, membrane fouling and oil retention of Synthetic PW stabilized with a cationic, anionic, zwitterionic or nonionic surfactant, were studied at various surfactant and salt concentrations. We discuss our results in the framework of the Young-Laplace (YL) equation, which predicts for a given membrane, pressure and oil-membrane contact angle, a critical interfacial tension (IFT) below which oil permeation should occur. We observe such a transition from high to low oil retention with decreasing IFT for the anionic (SDS), cationic (CTAB) and non-ionic (TX) surfactant, but at significantly higher critical IFTs than predicted by YL. On the other side, for the zwitterionic DDAPS we do not observe a drop in oil retention, even at the lowest IFT. The discrepancy between our findings and the critical IFT predicted by YL can be explained by the difference between the measured contact angle and the effective contact angle at the wall of the membrane pores. This leads to a surfactant-dependent critical IFT. Additionally, our results point out that zwitterionic surfactants even at the lowest IFT did not present a critical IFT and exhibited low fouling and low oil permeation.

Experimental Study on the Effect of ASP Flooding on Improving Oil Recovery in Low Permeability Reservoirs Based on a Partial Quality Tool

In order to solve the problem of the poor oil displacement effect of high molecular weight alkali/surfactant/polymer (ASP) solution in low permeability reservoirs, Daqing Oilfield uses a partial quality tool to improve the oil displacement effect in low permeability reservoirs. In the formation, the partial quality tool degrades the polymer through active shearing action, reducing the molecular weight of the polymer, to improve the matching degree to the low permeability oil layer and the oil recovery. In order to study the ability of the partial quality tool to improve the oil displacement effect, the matching degree of high molecular weight ASP solution to low permeability cores is studied, and the ability of quality control tools to change the molecular weight is studied. Then, experimental research on the pressure and oil displacement effect of high molecular weight ASP solution before and after the actions of the partial quality tool is carried out. The results show that ASP solutions with molecular weights of 1900 × 104 and 2500 × 104 have a poor oil displacement effect in low permeability reservoirs. After the action of the partial quality tool, the injection pressure is reduced by 5.22 MPa, and the oil recovery is increased by 7.79%. The injection pressure of the ASP solution after shearing by the partial quality tool is lower than that of the ASP solution with the same molecular weight and concentration without shearing, but the oil recovery is lower. On the whole, the use of the partial quality tool can obviously improve the oil displacement effect in low permeability reservoirs.

Influence of size and surface acidity of silica nanoparticles on inhibition of the formation damage by bentonite-free water-based drilling fluids. Part II: dynamic filtration

Although the application of nanoparticles in drilling fluid has been reported under static test by our research group, understanding inhibition formation of damage by filtration volume reduction in porous media under dynamic conditions is still a crucial issue. In this research, synthesised silica nanoparticles modified with acid treatment (Si11A) evaluated in previous results in the bentonite-free water-based drilling fluid (BFWBM) in static tests were analysed in the coreflooding test under dynamic and reservoir conditions. Si11A nanoparticles were evaluated by permeability return tests under reservoir conditions overburden, pore, and overbalance pressures, and temperatures of 3000 psi, 1700 psi, 1200 psi, and 87 °C, respectively. Coreflooding test with a concentration of 0.1 wt% Si11A nanoparticles based on our previous work showed a reduction in the filtration volume by 77%, decreasing the formation damage by 51% compared to the drilling fluid without nanoparticles. Also, the oil recovery obtained with the best design fluid using the Si11A nanoparticles was 10% higher than the baseline. Additionally, the effluents of crude oil obtained from permeability return test were evaluated at reservoir temperature using a rotational rheometer at shear rates varying between 1 and 100 s−1, obtaining a reduction of the viscosity up to 28% during nine pore volume injected using the BFWBM with S11A nanoparticles. The role of the nanoparticles in the drilling fluid is the rapid deposition in the mudcake to enhance the properties, the subsequent filtration volume reduction, and the enhancement of the petrophysics properties may be described by dynamic filtration curves, effective oil permeability and relative permeability curves.

Enabling phase transition of infused lubricant in porous structure for exceptional oil/water separation

The fundamental mechanism behind oil/water separation materials is their surface wettability that allows either oil or water to pass through. The conventional materials for oil/water separation generally have extreme wettability, namely superhydrophilic for water separation and superhydrophobic for oil separation. Using easily accessible materials that are medium hydrophobic or even relatively hydrophilic for preparing highly efficient oil/water separators have rarely been reported. In this work, a new strategy by triggering phase transition of infused lubricant from liquid to solid state in porous structure is realized in fabricating slippery lubricant infused porous structure for oil/water separations. By infusing polyester fabric with coconut oil, after phase transition, excellent water repellency and oil permeability by an absorbing-permeating mechanism are achieved, despite the low water contact angle on the new material. Although the new phase transformable slippery lubricant infused porous structure, features much milder hydrophobicity than conventional oil/water separators, it can remove diverse types of oil from water with high efficiencies. The phase transformable slippery lubricant infused porous structure is able to maintain their water repellency after immersing in high concentration salt (10 wt% NaCl), acid (25 % HCl), alkaline (25 % NH3·H2O) solutions for 120 h, showing remarkably functional durability in harsh environment. The lubricant phase transition mechanism proposed in this study is universally applicable to porous substrates with various chemical compositions and pore structures, such as porous sponges or even daily life breads, for creating efficient oil/water separators, which can serve as a novel accessible design principle of phase transformable slippery lubricant infused porous structure for eco-friendly oil/water separators.