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When surfactant is used as emulsifier, the stability of emulsion is often greatly reduced with the influence of reservoir conditions (temperature, pressure, salinity, etc.), which shortens the validity period of emulsion. Pickering emulsion has a wide range of applications in the oil and gas field due to its advantages of good stability and easy regulation. In this article, the formation, stabilization mechanism, and influencing factors of Pickering emulsions were introduced, and the application status and prospects of Pickering emulsions in oil and gas field were summarized. It was pointed out that Pickering emulsion has many advantages and important research value when applied in deep strata and complicated reservoirs. It is expected that this article can effectively reflect the application value of Pickering emulsion in oil and gas field and promote the application of Pickering emulsion in petroleum industry.

In this paper, the Grand Canonical Monte Carlo (GCMC) method was used to explore the effects of four pore structures (disordered pore, wedge pore, carbon nanotube and slit pore structures) and surface curvature of activated carbon on the adsorption and separation of CO2/N2. On the whole, carbon nanotubes have the greatest selectivity for CO2, followed by disordered pores, wedge pores and slit pores. The effect of pore structure on the interaction energy of gas molecules is similar to that of selectivity, in which the fluid-solid potential energy between adsorbates and adsorbents plays an important role. Due to the different affinity between adsorbate molecules and activated carbon, CO2 with high affinity is more sensitive to the change of pore size. Therefore, under high pressure, the density of CO2 in the slit pore is greater than that in the wedge pore. However, N2 with poor affinity is limited by the surface area, resulting in the density of it in the wedge pore is always higher than that in the slit pore. Although the existence of non-six membered corannulene rings in activated carbon can’t always cause the increase of specific surface area, the surface curvature of activated carbon caused by it can increase strong energetically adsorption sites. Hence, the surface curvature plays a positive role in the adsorption density, interaction energy and CO2 selectivity. The discovery of CO2/N2 adsorption and separation at the molecular level is expected to provide valuable insights.

To effectively investigate the influence of activated carbon on the adsorption of volatile organic compounds (VOCs), physical and chemical factors of activated carbon including pore wall thickness, pore size, and functional groups were studied using grand canonical Monte Carlo (GCMC) simulation. In addition, benzene and acetone were taken as two representative components of VOCs. Simulation results was presented by the changes in characteristics of benzene and acetone. The results show that at the saturated vapor pressure (P0), the adsorption density hardly varies with the mentioned factors of activated carbon. Differently, the saturated adsorption capacity increases considerably with the rise of pore size or the reduction of pore wall thickness, and the rise of pore size also leads to a dramatic increase in adsorption layer and a subsequent fall in ordering. However, when the pressure is less than 0.001P0, the monomolecular interaction energy and the isosteric heat are strengthened greatly with the addition of carboxyl and amino groups, while the threshold pressure shows an opposite change to the monomolecular interaction energy. In the meantime, the decrease of pore size or the increase of pore wall thickness will result in the same results. Findings in this paper can provide valuable insights into the microscopic mechanisms of the adsorption between activated carbon and VOCs.

Water-sensitivity damage is inevitable during hydraulic fracturing for tight reservoir stimulation. A polymer clay stabilizer is the most effective and commonly used agent for reducing this kind of permeability damage. However, due to the small pore throat radii of tight reservoirs, polymers may be captured and detained, resulting in secondary permeability damage caused by polymer plugging. Therefore, it is necessary to clarify the matching relationship between the relative molecular mass of the clay stabilizer and the permeability of tight cores, which has not been reported yet. In response to this problem, the residual resistance factor and the permeability damage rate of PDMDAAC (poly dimethyl diallyl ammonium chloride, a kind of commonly used polymer clay stabilizer) to tight cores from Xinjiang Oilfield were investigated in cores with permeabilities of 0.10 × 10

The composite flooding system composed of a surfactant and nanoparticles has shown great application potential in enhancing oil recovery. However, at present, these research studies are mainly focused on anionic surfactants. Relatively speaking, alkanolamide (CDEA), a nonionic surfactant, has the characteristics of a small adsorption amount on the rock surface, no cloud point, good temperature resistance, and good salt resistance. However, to the best of our best knowledge, there is no research report on the composite flooding system composed of CDEA and nanoparticles. Therefore, the surfactant/nanoparticle (S/NP) flooding system based on CDEA and nano-SiO2 was studied in this paper. The S/NP flooding system (0.1% CDEA + 0.05% SiO2) was constructed based on the performance in reducing the oil-water interfacial tension (IFT) and the stability of the composite system. The IFT between the S/NP flooding system and the crude oil can reach ultra-low values (3 × 10-3 mN/m), and there is no obvious sedimentation within 72 h. The sandpack flood tests show that the oil recovery rate is increased by 16.8% compared with water flooding and finally reaches 58.2%. Based on micromodel flooding tests, the mechanisms of the S/NP flooding system are studied as follows: the synergistic effect of nanoparticles and surfactants can re-enforce its oil-water interface performance and improve the oil displacement efficiency and the Jamin effect of emulsified oil droplets, combined with the thickening property and retention plugging of nanoparticles, improves the sweep efficiency. As the surfactant and nanoparticle used in this study are commercially available industrial products, the research results have important guiding significance for promoting the industrial application of surfactant/nanoparticle composite flooding technology.

The superhydrophilic/underwater superoleophobic (SUS) membrane has attracted significant attention in the separation process of oily wastewater, especially for the oil-in-water emulsions, due to high separation efficiency and remarkable antifouling performance. In this review, the related wetting mechanisms of SUS membranes, design criteria of constructing rough surface, and recent developments in materials with SUS membranes for separating oily wastewater are detailed. According to the creative design of the micro-nano scale hierarchical surface morphology of SUS membranes, various porous membranes with surface roughness, including xD (herein, x represents 0 ~ 3) micronano, are systemically analyzed. In each section, various types of membranes are also presented with design ideas, base materials, and preparation methods. Then, the high-energy rough micro-nano structures are proposed for constructing on the surface of the membrane as a more effective method for preparing SUS membranes. Finally, conclusions and perspectives for future research are provided in depth according to the existing problems in this field.

Hydraulic fracturing technology is the most important stimulate method to develop unconventional oil and gas resources. The incomplete flowback of the fracturing fluid causes great seepage resistan...

To analyse the effects of initial water content (IWC) and temperature on the adsorption behaviour of VOCs on activated carbon (AC), the grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) methods were used. Benzene and acetone are regarded as two representative components of VOCs, and their adsorption properties in AC models with four different IWC at 298.15 K were investigated. Their adsorption properties at four different temperatures (278.15, 288.15, 298.15, and 308.15 K) were also investigated. The simulated pressures were set in the range of 3 × 10−4 to 3 kPa (benzene) and 10 × 10−4 to 10 kPa (acetone). The results show that water molecules can impede the adsorption of benzene and acetone, decreasing the saturated adsorption capacity, the isosteric heat, and monomolecular interaction energy. However, the pre-loaded water molecules can enhance the electrostatic interaction at low pressure, which affects the isosteric heat and monomolecular interaction energy, but the pore volume is still the main influencing factor. Before reaching the saturated adsorption capacity, the higher the temperature, the lower the adsorption capacity, and the monomolecular interaction energy follows the same trend. The results provide mechanistic insights into how the IWC and temperature affect the adsorption properties of AC for VOCs.

Clay stabilizer is the topic of a great number of studies, particularly in petroleum engineering. The organic cationic polymer is a kind of clay stabilizer with excellent anti-swelling effect. However, for tight reservoirs, the organic cationic polymer type clay stabilizers tend to increase the permeability damage caused by retention and blockage of stabilizers. Therefore, stabilizers with low molecular weight are necessary for tight reservoirs. The inhibition properties and the mechanisms of ethylenediammonium dichloride (EDD) were studied in this paper. The clay inhibition properties were studied from three aspects: swelling inhibition, clay sedimentation, and particle size distribution. Results showed that the anti-swelling rate reaches 91.98%. Control experiments showed that EDD had better inhibition property than KCl, NH4Cl, and poly dimethyldiallyl ammonium chloride (PDMDAAC). The inhibition mechanisms, studied from the aspect of surface hydrophobicity, surface charge, interlayer water content, and crystal spacing, can be concluded as that EDD reduces clay electronegativity and enhances the hydrophobicity of the clay surface, thereby keeping clay in a stable state. Compatibility tests showed that EDD can be used in guar based fracturing fluid. This study provides an alternative clay stabilizer for hydraulic fracturing.

Welan gum is one of the most promising polymers used in polymer flooding for enhancing oil recovery, due to its excellent temperature resistance and salt-tolerance performance. However, welan gum, as a polymer with higher molecular weight, can be adsorbed and detained in the pore throat of the reservoir, which is characterized by a smaller size. Montmorillonite, a kind of clay mineral with high content in reservoir rocks, has strong adsorption capacity. Therefore, the adsorption behavior of welan gum on montmorillonite, as well as its influencing factors, are studied in this paper. The results show that the adsorption capacity is 2.07 mg/g. The adsorption capacity decreased with the increase in temperature. Both acidic and alkaline conditions reduced the adsorption capacity. The existence of inorganic salt affected the adsorption capacity. In addition, the higher the cation value, the lower the adsorption capacity. The characterization tests showed that the adsorption of welan gum on montmorillonite was characterized by physical adsorption and surface adsorption, indicating that there were no changes in the internal structure of montmorillonite. This study provides feasible methods to reduce the amount of welan gum adsorbed on montmorillonite, which is of great significance for reducing the permeability damage caused by welan gum adsorption and promoting the application of welan gum in polymer flooding for enhancing oil recovery.

Graphene and its derivatives, with their unique two-dimensional structures and excellent physical and chemical properties, have been an international research hotspot both in the research community and industry. However, in application-oriented research in the oil and gas industry they have only drawn attention in the past several years. Their excellent optical, electrical, thermal and mechanical performance make them great candidates for use in oil and gas exploration, drilling, production, and transportation. Combined with the actual requirements for well working fluids, chemical enhanced oil recovery, heavy oil recovery, profile control and water shutoff, tracers, oily wastewater treatment, pipeline corrosion prevention treatment, and tools and apparatus, etc., this paper introduces the behavior in water and toxicity to organisms of graphene and its derivatives in detail, and comprehensively reviews the research progress of graphene materials in the upstream oil and gas industry. Based on this, suggestions were put forward for the future research. This work is useful to the in-depth mechanism research and application scope broadening research in the upstream oil and gas industry.

Carbon-silica composites with nanoporous structures were synthesized for the adsorption of volatile organic compounds (VOCs), taking tetraethyl orthosilicate (TEOS) as the silicon source and activated carbon powder as the carbon source. The preparation conditions were as follows: the pH of the reaction system was 5.5, the hydrophobic modification time was 50 h, and the dosage of activated carbon was 2 wt%. Infrared spectrum analysis showed that the activated carbon was dispersed in the pores of aerogel to form the carbon-silica composites material. The static adsorption experiments, dynamic adsorption-desorption experiments, and regeneration experiments show that the prepared carbon-silica composites have microporous and mesoporous structures, the adsorption capacity for n-hexane is better than that of conventional hydrophobic silica gel, and the desorption performance is better than that of activated carbon. It still has a high retention rate of adsorption capacity after multiple adsorption-desorption cycles. The prepared carbon-silica composites material has good industrial application prospects in oil vapor recovery, providing a new alternative for solving organic waste gas pollution.

Liquid nitrogen (LN2) fracturing is a promising new technology for unconventional reservoir simulation because it can effectively solve problems related to low permeability, low brittleness, and water shortage. The present work conducted a series of permeability and strength property-related experiments to evaluate the effect of LN2 cooling on the permeability and mechanical characteristics of anisotropic shale. The main findings of the study are as follows: (1) The influence of the bedding direction on the permeability of anisotropic shale cannot be eliminated by LN2 cooling. LN2 cooling could effectively increase the initial natural damage and the pore space of anisotropic shale, possibly increasing the volume of reservoir stimulation and provide more channels for the seepage and migration of oil and gas. (2) After LN2 cooling, the strength and brittleness of shale are obviously reduced, leading to the decrease in the ability of shale to resist deformation and failure, thereby helping to decrease the initiation pressure of reservoir stimulation. (3) The brittleness of shale will markedly increase during cryogenic fracturing, thus helping to form more complex fracture networks. Based on the present research, LN2 fracturing has obvious advantages compared with hydraulic fracturing in increasing the volume of reservoir stimulation. The results of this study are instructive for understanding the synergistic mechanism of LN2 fracturing and evaluating the effectiveness of reservoir simulation.

The stability of a shale containing smectite with different exchangeable cations (Na+, Ca2+) was improved using optimum solutions containing polyether amine (PA), poly-alcohol (PO) or KCl. Two types of shale samples with Na+ and Ca2+ as the main exchangeable cations, respectively, were used and the optimized solutions were determined using X-ray diffraction (XRD), an adsorption test, an oedometer swelling test, and an immersion test. The use of KCl prevented intercalation of PA or PO and maintained the stability of the Na-smectite-bearing shale. PA or PO adsorption reduced water adsorption sites on the clay layer, and K+ reduced hydration of exchangeable Na+, resulting in good shale stability in mixed solutions of KCl+PA, and KCl+PO. More stable shale was achieved in KCl+ PA mixed solution, whereas in the KCl+ PO solution the transport of water or solute molecules in the shale was reduced. In the shale containing mainly Ca-smectite, PA, PO and KCl maintained shale stability when applied separately or in common, as PA or PO cannot exchange Ca2+ in the smectite interlayer. As a result, PA or PO should be used together with KCl during drilling in shale formations containing Na-smectite, whereas in shales with Ca-smectite, PA, PO or KCl may be used separately.

Welan gum (WLG) has been reported being used in chemical flooding and hydraulic fracturing for high-temperature and high-salinity reservoir development due to its good temperature resistance and salt tolerance properties. The adsorption and retention of WLG in reservoir rocks will reduce the reservoir permeability and affect the economic development of oil and gas fields. However, there are no reports about the adsorption of WLG on quartz sand. Therefore, in this study, standard curve of absorbance-WLG concentration was established by anthrone colorimetry method. The adsorption behavior accorded with the Langmuir adsorption isotherm. The adsorption capacity was 4.01 mg/g. By means of Fourier transform infrared spectrum analysis, X-ray diffraction technology, thermogravimetric analysis, scanning electron microscope, optical microscope, and contact angle measurement, it is confirmed that the adsorption was physical adsorption and surface adsorption, and did not have obvious influence on crystal spacing and wettability of quartz sand. Based on this, the study of the influence of reservoir conditions showed that: the adsorption capacity decreased with the increase of temperature; pH value had little effect; the adsorption capacity first increased and then decreased with the increase of inorganic salt content, and this trend varied with the types of inorganic salts.

There are many geological hazards in shallow formations associated with oil and gas exploration and development in deep-water settings. Abnormal pore pressure can lead to water flow and gas and gas hydrate accumulations, which may affect drilling safety. Therefore, it is of great importance to accurately predict pore pressure in shallow deep-water formations. Experience over previous decades has shown, however, that there are not appropriate pressure calculation methods for these shallow formations. Pore pressure change is reflected closely in log data, particularly for mudstone formations. In this paper, pore pressure calculations for shallow formations are highlighted, and two concrete methods using log data are presented. The first method is modified from an E. Philips test in which a linear-exponential overburden pressure model is used. The second method is a new pore pressure method based on P-wave velocity that accounts for the effect of shallow gas and shallow water flow. Afterwards, the two methods are validated using case studies from two wells in the Yingqiong basin. Calculated results are compared with those obtained by the Eaton method, which demonstrates that the multi-regression method is more suitable for quick prediction of geological hazards in shallow layers.

The dome roof tank (DRT) is always a main equipment for oil products storage. However, the mechanism of the heat and mass transfer for the oil vapor-air in the tank gas space remains unclear when the DRT is subjected to the solar radiation. Therefore, by considering storage conditions (e.g., the solar radiation intensity and liquid height) and taking n-hexane as a representative of light oils, and based on the Fluent software and user-defined functions (UDFs) programming, a two-dimensional calculation method and the relevant theoretical model were numerically developed to simulate and reveal the transfer mechanism under the complex storage process. Meanwhile, the feasibility of the model was verified by a self-built experimental platform for the DRT evaporation loss investigation. Under the solar radiation to a 1000 m3 DRT, the simulation results show: (1) The gas space temperature distribution can be accurately calculated, and the average temperature decreases with increasing liquid level; (2) There is a distinct counterclockwise eddy and an evident velocity boundary layer close to the wall and roof of the gas space, and the maximal gas velocity is within 0.08–0.49 m s−1, which is closely related with the storage liquid height and time; (3) The vapor concentration in the gas space increases from top to bottom with an obvious high-concentration layer near the liquid surface, and the average concentration increases with increasing liquid level and storage time; (4) The static breathing losses increase positively with the liquid level. The mean daily loss rates for n-hexane are approximately 7.37 g t−1, 20.9 g t−1, and 6.36 g t−1 for the spring equinox, summer solstice, and winter solstice, respectively. Further, the year-mean daily loss rates are about 11.5 g t−1, and 20.1 g t−1 for n-hexane and gasoline, respectively, and the correspondingly the total loss rates for a year are about 4.2 kg t−1 and 7.35 kg t−1. The research results can provide important theoretical support and design reference for reducing the breathing loss and improving the enterprise management level.

Due to the high rate of proppant flowback after hydraulic fracturing stimulations, surface modified quartz sand proppants with excellent proppant flowback control abilities, self-aggregating proppants, were prepared. These surface modified proppants can aggregate together spontaneously and form a proppant column in water based liquid environment. Analyses show that the strong hydrogen bonds contribute to the absorption of the surface modifier onto the proppants, and the softening effect of the water to the polymer coating prompts the connection between the proppants. Scanning electron microscope pictures show that proppant particles are stacked together tightly. The stable structure contributes to the macroscopic stability of the proppant column. The maximum sand free flow rate of the model packed with modified proppants is 2.8 times larger than that of untreated proppants by average, indicating that the self-aggregating proppants exhibit excellent proppant flowback control abilities. In addition, fines control tests show that the modified proppants can also prevent the migration of the formation fines effectively, reducing the conductivity loss caused by particle migrations. By virtue of the reaggreating property and the encapsulation action of polymer coating to the crushed fragments, the fracture conductivities are increased by 3 times even at large closure stresses. The results provide a new alternative for proppant flowback control while do little damage to the permeability of the proppant pack.

With regard to ordinary heavy oil reservoirs which are not suitable for thermal methods, alkaline-surfactant-polymer (ASP) flooding exhibits great potential for enhancing heavy oil recovery. But for the formation water with high content of Ca 2+ and Mg 2+ ions, conventional ASP flooding always causes precipitation of a large amount of Ca and Mg salts which are damage to reservoirs. In this study, organic alkali-surfactant-polymer (OASP) flooding system is established, which exhibits good compatibility with the brine containing high-valent metal ions. The interfacial tension tests show that the combination of Shengli petroleum sulfonate (SLPS) and ethanolamine exhibits a good synergistic effect, and acquires an ultralow interfacial tension. Based on micromodel flooding tests, the mechanisms of OASP flooding system are studied as follows: the organic alkali in OASP system reacts with the acidic component of heavy oil and promotes the formation of water-in-oil (W/O) emulsion in heavy oil, thus increasing the flow resistance of flooding liquid and improving the sweep efficiency of normal ASP system. The generated surface active materials and surfactant can decrease the interfacial tension to an ultralow level, which could easily initiate the emulsion dispersion of crude oil, form the O/W emulsion, and improve the oil displacement efficiency. The sandpack flood results demonstrate that the oil recovery is increased by about 20%, and the recovery increases with the increase in organic alkali concentration. Therefore, the organic alkali-surfactant-polymer flooding technology can be developed into a new type of economically and technically feasible compound flooding technology suitable for ordinary heavy oil reservoirs with high content of Ca 2+ and Mg 2+ ions. Moreover, OASP flooding technology shows broad application prospects in improving the recovery of ordinary heavy oil reservoirs in Shengli Oilfield.

In order to solve the problem of proppant flowback in postfrac fracturing fluid flowback treatments and hydrocarbon productions, new heterocyclic polymer modified proppants were introduced. The most important characteristic of the modified proppants is self-aggregation in the water environment. Due to this special character, an evaluation method based on ultrasonic oscillation effect is developed to measure the aggregating strength of the proppants congeries, with which the optimal formula and the recommended dosage are determined. By virtue of the reaggregating property of the modified proppants, which is different from the one-time bonding effect of resin coated proppants, the fracture conductivity and the proppant flowback control ability are improved greatly. Experimental results show that with the dosage of 1.0% of the PFVP, the strength of the reaggregating column decreases by 54.6% after ten times of collapse and reaggregation, which is even big enough for proppant flowback control. The larger the dosage of PFVP is, the higher the strength of the reaggregating proppant column regains. Compared with untreated proppants and resin coated proppants, the maximum sand free flow rate of the modified proppants increases by 80.6% and 39.8%. The higher the closure stress is, the more obvious the proppants flowback control ability is. In addition, the formation fines adsorption property of the PFVP modified proppants endows the self-cleaning property of the flow channels in the fracture. The results provide a new alternative for proppant flowback control, especially in unconsolidated sandstone formation with high closure stress.

Due to the high water content ratios after hydraulic fracturing stimulation treatments in the bottom-water-drive reservoirs, a surface modified quartz sand proppant with the performance of water inhibition and oil enhancement was developed. This surface modified proppant (YS03 proppant) indicates the following advantages, such as, no-heating in the preparation process, simple operation, and short reaction time, making it suitable for “On-the-fly” treatment, which will greatly reduce the impact of storage and transportation. The evaluation experiments show that the contact angle is up to 151° with little change even at 80 °C, which indicates YS03 proppant has strong hydrophobicity. The crush rates of the quartz sand at 52 MPa (69 MPa) are reduced from 3.69% (10.30%) to 1.81% (5.11%), making it applicable to hydraulic fracturing. The core flowing experiments demonstrate that the NFRR is 5.51, and the fracture conductivity experiments show that YS03 proppant pack can effectively inhibit the flow of the aqueous phase and promote the flow of the oil phase. In addition, the fines adsorption experiments manifest that the YS03 proppant pack has an excellent self-cleaning property, which can maintain flow channels for the hydrocarbon production for a long time after the hydraulic fracturing treatment.

Hydraulic fracturing technology is the most effective stimulation method to develop hydrocarbons in tight reservoirs, but the invading of fracturing fluid into the reservoir matrix often causes permeability damage, resulting in reducing the effectiveness of the stimulation treatments. Therefore, in this paper, for tight cores with permeability of 0.10 × 10−3μm2, 0.05 × 10−3μm2 and 0.01 × 10−3μm2, the damage laws were studied through flow experiments. The results are as follows: taking cores with the permeability of 0.05 × 10−3μm2 as an example, the damage rate of water-sensitivity damage, water-locking damage, and solid-phase damage were 12%, 10% and 9%, respectively, indicating that water-phase damage was the major damage; as the initial core permeability decreases, the water-sensitivity damage rate and water-locking damage rate increase, while the solid-phase damage rate decreases slightly, but the total damage rate increases. In addition, the control methods of liquid-phase damage caused by the invading fracturing fluid were studied, and the results are as follows: increasing the flowback volume is effective to control water-locking damage, but has no obvious effect to water-sensitivity damage; for polymer clay stabilizer, the relative molecular weight (when changing from 1 × 104 to 11 × 104) affect the effect of water-sensitivity damage (the permeability damage rate increased by 141% for cores with the permeability of 0.05 × 10−3μm2), indicating that the molecular weight of clay stabilizer should be fully considered; for surfactant-based cleanup additive, when the oil/water interfacial tension (IFT) was reduced from 1.26 mN/m to 0.26 mN/m, the core damage rates were reduced by 44%, 36% and 34%, respectively, indicating that the reduction of IFT was beneficial to water-locking damage control. This paper is useful for further studying the damage law of fracturing fluid to tight reservoir and the control method of water-phase damage, and provide some references for the efficient development of tight hydrocarbon resources.

Internal floating-roof tanks (IFRTs) are widely used to store light oil and chemical products. However, if the annular-rim gap around the floating deck becomes wider due to abrasion and aging of the sealing arrangement, the static breathing loss from the rim gap will be correspondingly aggravated. To investigate the oil-vapor migration and emissions from an IFRT, the effects of varying both the floating-deck height and wind speed on the oil-vapor diffusion were analyzed by performing numerical simulations and wind-tunnel experiments. The results demonstrate that the gas space volume and the wind speed of an IFRT greatly influence the vapor-loss rate of the IFRT. The larger the gas space volume, the weaker the airflow exchange between the inside and outside of the tank, thereby facilitating oil-vapor accumulation in the gas space of the tank. Furthermore, the loss rate of the IFRT is positively correlated with wind speed. Meanwhile, negative pressures and the vortexes formed on the leeward side of the tank. In addition, the higher concentration areas were mainly on the three vents on the downwind side of the IFRT. The results can provide important theoretical support for the design, management, and improvement of IFRTs.

Metal organic frameworks (MOFs) and reduced graphene oxide (RGO) are used to modify photoanodes of dyes sensitized solar cells (DSSCs) to improve their photovoltaic performances. The MOFs are found that bring about a significant enhancement of the BET area of photoanodes, which endows a high dye adsorption capacity. Moreover, the added MOFs introduces an improved incident photon to electron efficiency because of the remarkably enhanced scattering power for the incident light. On the other hand, in the presence of RGO provides a fast transport channel for photo-induced electrons, which depresses the dark current of the resulting devices. After optimizing the mass fraction of MOFs and RGO, the synergy has been achieved. Moreover, by using a graphene-based counter electrode, the photovoltaic performances of the resulting full-carbon DSSCs are detected. The short-circuit current, open-circuit voltage, fill factor (FF) and energy conversion efficiency (η) reach 18.6 mAcm−2, 682 mV, 0.608 and 7.67%, indicating the potential application prospection of the as-prepared photoanodes.

A calculation method was established for numerically simulating the evaporation of oil products and vapor diffusion from the annular rim gap of the floating deck in an internal floating-roof tank (IFRT) under the unsteady operating state. The proposed method is based on the “thin film” theory, Stefan diffusion, and the realizable k-e turbulence model. The accuracy of the calculation method was verified by wind tunnel experiments. Considering various operating conditions, the oil evaporation and vapor diffusion were investigated, and the mass transfer mechanism in the gas space was revealed. The results show that the vapor concentration isosurface in the gas space exhibits a “wave-shaped” distribution, and the vapor concentration can easily accumulate in the windward side of the gas space under the influence of a wind speed. In addition, the evaporation rate is closely related to the type of oil product, and the evaporation rate increases with increasing wind speed or floating deck height. The evaporation rate was initially in a fluctuating state and stabilized soon. Furthermore, when the width of the annular leaking rim gap was 0.2 m in a gasoline IFRT with a volume of 1000 m3, the vapor concentration in the most of the gas space was higher than the lower explosive limit; the region with a high vapor concentration will further expand with increasing wind speed. The calculation method and the numerical simulation results in this study can provide important theoretical support for reducing oil evaporation loss, controlling air pollution, and ensuring safe operation of IFRTs.

Water production is getting worse along with the continuous water injection in the reservoir with fracture, but common hydrogels cannot be successfully applied for water shutoff due to its poor resident ability in fracture. In this work, an interpenetrating network hydrogel has been developed innovatively by polyvinyl alcohol (PVA) fiber and common polyacrylamide (PAM) hydrogel. Plugging ability, long-term thermal stability and the interaction between PVA fiber and hydrogel were detailedly studied. Results show that PVA fiber is beneficial to the stability of the PAM hydrogel, and the syneresis rate can be decreased from 30% to 3% on the 120th day. PVA fiber accelerates the hydrogel gelation, and the high concentration of fiber leads to good hydrogel strength. PVA fiber increases the amount of the bound water in hydrogel, leading the hydrophilcity increase of hydrogel. An interpenetrating network is formed on the micrometer level, resulting from the three-group crosslinking among polymer, cross-linker and fiber. Compared with common PAM hydrogel, the interpenetrating network hydrogel has better water shutoff effect and EOR performance. Core flow experiment and micromodel test show that the interpenetrating network hydrogel forms an effective bridge in fracture, and it is hard to be moved due to the water washing. The introduction of fiber to hydrogel is an innovative research, which not only improves the water shutoff effect of hydrogel in fracture, but also provides reference to increase the performance of drilling fluid, fracturing solution and EOR polymer utilized in petroleum engineering.

Channel fracturing is a promising technique for unconventional reservoir stimulations. Fibers bonded proppants and resin coated proppants are the two common technologies used for heterogeneous proppant placement. This paper discusses a new kind of surface modified proppant with the unique performance of self-initiated aggregating property in distilled water and guar gum fracturing fluid, which is suitable for keeping proppant cluster together during transportation in the wellbore and fracture. The changes of the zeta potential of the proppant grains and the intertwining effect of the polymer coating account for the self-initiated aggregating property. An evaluation method for measuring the self-initiated aggregating strength of the proppant column was introduced, with which the aggregating speed and the aggregating perdurability were evaluated. Due to the re-aggregating property, the fracture conductivity was significantly improved, and the higher the closure stress, the more obvious the advantages. The findings of this study provide a new alternative for channel fracturing. [Received: November 4, 2016; Accepted: April 3, 2017]

Emulsion flooding has great potential for enhancing the recovery of heavy oil, especially for reservoirs in which the oil recovery by water flooding is low and thermal methods are not suitable. This study presents a study of nanoparticle-surfactant stabilized emulsion to enhance heavy oil recovery in waterflooded heavy oil reservoirs. The phase behavior tests and rheology studies were first performed to investigate the influence of nanoparticle on the stability and bulk rheological properties of the emulsion system. Then, the core flooding and microscopic visualization tests were conducted for investigating the displacement mechanisms for enhanced heavy oil recovery by nanoparticle-surfactant stabilized emulsion. The phase behavior tests and rheology studies show that the addition of nanoparticles can not only improve the stability of the emulsion, but also greatly increase the bulk viscosity of emulsion. The core flooding conducted with the emulsion co-stabilized by nanoparticle and surfactant show a marked improvement in oil recovery over the surfactant-stabilized emulsions. The tertiary oil recovery can reach over 40% of the initial oil in place (IOIP) for crude oil with the viscosity of 350 mPa•s at 50 °C. The micromodel tests indicate that the nanoparticles can thicken the emulsion to the desirable mobility, which can damp the viscous fingering phenomena to dramatically improve sweep efficiency. In addition, the heavy oil can be emulsified into the water phase to form oil-in-water emulsions with the aid of the surfactant. These results demonstrate that the nanoparticle-surfactant stabilized emulsion has a great potential for enhanced oil recovery in waterflooded heavy oil reservoirs.