Foam Fluid Research Articles

Synergistic improvement of foam stability with SiO2 nanoparticles (SiO2-NPs) and different surfactants

Foam fluids are widely used in petroleum engineering, but long-standing foam stability problems have limited the effectiveness of their use. The study explores the synergistic effects and influencing factors of SiO2 nanoparticles (SiO2-NPs) with different wettability properties and three different surfactants. The paper investigates the foaming performance of different types of surfactants and analyzes and compares the stability of foam after adding hydrophilic and hydrophobic SiO2-NPs from macroscopic as well as microscopic perspectives, and the effects of temperature and inorganic salts on the stability of mixed solutions. The experimental results show that: 1) hydrophilic nanoparticles can significantly enhance the foam stability of amphoteric surfactants, with a small increase in the foam stability of anionic and cationic surfactants; 2) The concentration of nanoparticles did not have a significant effect on the stability of the cationic surfactants and this conclusion was verified in the experimental results of the surface tension measured below;3) The cationic surfactants showed better temperature resistance at temperatures of 50–90 °C. Both amphoteric surfactant solutions with the addition of hydrophilic SiO2-NPs or hydrophobic SiO2-NPs significantly improved the temperature resistance of the foam at high temperatures. The anionic surfactant solution with hydrophobic SiO2-NPs did not enhance the solution temperature resistance; 4) The surface tension of the surfactant solution gradually increases with increasing concentration of hydrophilic or hydrophobic SiO2-NPs and then levels off; 5) the hydrophilic SiO2-NPs had a significant effect on the salt tolerance of the anionic and amphoteric surfactant solutions. The salt tolerance of cationic surfactant solutions with hydrophobic SiO2-NPs was better than that of surfactants with hydrophilic SiO2-NPs.

High thermal stability of foams stabilized by graphene oxide and zwitterionic surfactant nanocomposites for fracturing applications

Developing foamed fracturing fluids with excellent efficiency and low formation damage has been essential to improve hydraulic fracturing performance in recent years. In the present study, a foamed fluid stabilized by a synthesized nanocomposite of graphene oxide and a zwitterionic surfactant (GO/SURF) was evaluated at temperatures 200–350 °F. In addition, the foam characteristics, such as thermal stability, bubble microstructure, and apparent viscosity, were also investigated. Static and dynamic experiments demonstrated that the SURF foam's stability and thermal adaptability enhanced at 200–350 °F due to introducing the GO/SURF nanocomposite. In addition, the foam-film microstructure of the GO/SURF-based foam maintained its small, regular spherical shape for four hours at 300 °F. Moreover, the apparent viscosity of the GO/SURF foam was higher than that of SURF foam at a shear rate and temperature of 300 s−1 and 350 °F, respectively. The improved performance displayed by GO/SURF can be ascribed to the adsorption of the GO/SURF nanocomposite at the bubble surface, which enhanced the mechanical strength of the foam layer. As a result, the foamed fracturing fluid stabilized by GO/SURF is superior to pure SURF foam and is recommended for utilization in hydraulic fracturing, especially in long fracturing stimulation applications at high temperatures.

In-situ emulsification synergistic self-profile control system on heavy oil reservoir development: Prescription construction and EOR mechanism investigation

Water flooding is a vital method used for developing heavy oil reservoirs. However, the fingering phenomenon is common because of the significant difference in water-oil mobility ratio, resulting in limited sweep efficiency and a low cumulative recovery factor. Viscosity reduction through emulsification and profile control using foam is of great potential to enhance oil recovery (EOR) in water flooding of general heavy oil reservoirs. The present work constructed an effective in-situ emulsification synergistic self-adjusting profile control system based on these two EOR pathways and investigated the performances of the proposed system, such as viscosity reduction via emulsification, foam plugging, and synergistic oil displacement. The results show that sodium octadecyl phenol polyoxyethylene ether sulfonate-4 (JNPM) with sound viscosity reduction, profile control, and oil displacement effects were synthesized through chlorination and sulfonation reactions. JNPM can reduce the oil-water interfacial tension and promote the emulsification of heavy oil in an effective way. It forms an unstable micron-scale oil-in-water emulsion, which is easy to induce oil-water separation of the produced fluid. The reduction in viscosity for JNPM exceeds 90%, whereas the foam produced by JNPM can adequately reduce the relative permeability of the displacement medium, and it is found that the resistance factor is higher than 25. The EOR mechanisms of JNPM include the following aspects. JNPM foam fluid has a stable plugging capability on the channeling channels of the displacement media, such as water and gas, which forcefully increases the residual oil sweep efficiency. JNPM peels off the residual oil on the pore wall through emulsification, thus the oil washing efficiency is improved. The droplets of oil formed by emulsification can block the channeling channels through the Jamin effect to further increase the conformance efficiency. In addition, when the small droplets deform and pass through the pores, they can sweep away the residual oil by dragging and entraining effects. The contributions of viscosity-reducing emulsification and foam plugging to EOR are 26.4% and 12.0% respectively during the viscosity-reducing foam flooding of JNPM.

Laboratory study on the rheology properties of nanoparticle-stabilized supercritical CO2 foam

Adding nanoparticles (NPs) into surfactant solution has been widely employed in improving foam stability in CO2 Enhanced Oil Recovery (EOR) applications. To help understand the foam flow characteristics in porous media, the rheology behavior of the NP-stabilized CO2 foam is experimentally investigated in this paper. The foam fluid is treated as a non-Newtonian fluid obeying the power law constitutive equation, and the effect of CO2 phase state, oil presence as well as solution salinity on the power law index, and the apparent viscosity of the NP-stabilized foam is scrutinized. Different rheology behavior between the NP-stabilized gaseous CO2 foam and the supercritical CO2 (ScCO2) foam is revealed in the both power law index and the apparent viscosity results. The NP-stabilized gaseous CO2 foam shows the rheology transition behavior from shear thickening to shear thinning with increasing shear rates and supplies maximal foam apparent viscosity of 27.7 mPa s, whereas the NP-stabilized ScCO2 foam shows the universal shear thickening behavior in the studied shear rate range with much higher maximum apparent viscosity of 95.8 mPa s. It is found the apparent viscosity of the NP-stabilized ScCO2 foam could reach up to 210.9 mPa s under the oil presence conditions, while 5 wt% NaCl existence in the aqueous solution could result in slightly lower apparent viscosity of 80.3 mPa s.

Magnetic quantum dots-stabilized foam fluid for enhanced oil recovery

Nanoparticle-stabilized foam fluid provided excellent efficiency in tertiary oil recovery, and a more appealing technique is to exploit reusable low-dimensional nanomaterials, which can achieve better oil-displacement efficiency during the period of global decarbonization. Herein, the magnetic quantum dots (MQDs) were synthesized and then modified by a silane-coupling ionic liquid (SIL) to produce unique quantum dots MQDs@SIL. A series of characterizations and foaming measurements reveal that MQDs@SIL with an average surface grafting density of 1.01 functional chains nm−2 at an ultra-low concentration (0.005 wt%) demonstrated distinct foam stability and salt resistance capability, as well as a unique defoaming performance in a constant magnetic field for regulated foam performance at high temperature. The stretched-straight functional chains and adequate hydrophilic-hydrophobic surface of MQDs@SIL substantially favor the nonreversible adsorption of MQDs@SIL on the gas–liquid interface, leading to an increased surface elasticity, and thus an enhanced foam stability. MQDs@SIL-stabilized foam liquid demonstrated exceptional plugging performance and achieved an enhanced oil recovery of 18.2 % in the stage of foam fluid flooding, exceeding most nanoparticle-stabilized foam fluids ever reported. Furthermore, MQDs@SIL with the unique magnetic property provided unique recycling and reusing benefits, emphasizing their potential applications for enhanced oil recovery.

The effective thermal conductivity of virtual macroporous structures

Recent developments in macroporous structures featuring metallic bodies are becoming a focus of research due to their improved load-bearing capacity and high specific surface area, making them potential candidates for thermofluidic applications. Through numerical modelling and simulations at the pore-scale, this paper examines the ability of virtual macroporous structures generated by sphere-packing models to predict the effective thermal conductivity of “bottleneck-type” macroporous structures. Simulations of virtual macroporous structures with monosized pores show the relative impact of key pore structure-related properties on effective thermal conductivity in such structures. The extension of these findings to bimodal and adapted designs results in an increase in fluid transverse capacity of these structures, causing an increase in the original monomodal pore volume by 17 and 30% respectively, while varying their capillary radius from 10 to 80 μm only results in a 10% increase in pore volume fraction. Overall, this study demonstrated that pore structure-related properties played an important role in conductive heat transfer, with material porosity being an influential property and inversely (non-linear) correlated with the effective thermal conductivity of the foam–fluid system. The contributions tendered by material pores and specific surfaces were minimal, and mathematical relationships were proposed between effective thermal conductivity, pore-structure-related properties, and fluid and solid thermal conductivity values. Modelling techniques such as this one could serve to optimize the thermal performance of macroporous structures, as well as to gain the benefits of being ultra-lightweight and having a high Young modulus.

Variation of the lift force components of a settling particle caused by structural evolution of flowing foam

Wet foam fluid with a settling particle, as a special gas-liquid-solid three-phase flow, is increasingly found in related engineering fields. However, the detailed microscopic evolution of foam structure, which influences migration of the settling particle, has not been fully understood. In this study, the forces, exerted on the particle by foam film and bubble pressure in the flow direction, are defined as the lift force components Fnx and Fpx, respectively. The flow of the wet foam with a circular settling particle is studied by numerical method, and the distribution characteristics of the bubble-bubble and bubble-particle separations in the flowing foam are shown. More importantly, the influences of the microscopic structural evolution of foam film, such as the bubble-particle contact, the bubble-bubble and the bubble-particle separations, on the lift force components are in detail discussed. It is found that both the bubble-bubble and the bubble-particle separations can cause decreasing lift force and relaxing film stress, and the instantaneous bubble-particle contact can significantly change the lift force components. At the film scale, this study reveals the correlation between the particle movement and the microscopic structural evolution of foam fluid.

Computational study on the three phase displacement characteristics of foam fluids in porous media

Foam technology has shown great potentials not only on enhancing oil recovery (EOR) but also on the Carbon Capture Storage Utilization (CCUS) applications. In this paper, the foam three phase displacement characteristics in the porous media is investigated based on the mechanistic Stochastic Bubble Population Balance (SBPB) model. With taking the foam generation rate Kg and maximum bubble density nmax as the key influential parameters, the dynamic distributions of the water, oil and gas phase saturations as well as the bubble densities along the foam flow direction are successfully obtained. Firstly, the overall computation frame is validated based on good agreements between the numerical and the reported experimental results on the foam displacement efficiency on water and oil phases. Then, the parameter studies are thoroughly performed concerning the two key factors of Kg and nmax in the SBPB model. Numerical results show the parameter of Kg dominates the foam flow behavoir in the inlet region of the porous media therefore doesn't show significant effect on the final oil and gas phase recovery rates. On the other hand, it is found larger nmax could lead to higher oil and water recovery ratio, which indicates to increase the nmax values of the foam fluid could act as the favorable means in oil recovery enhancement practices.

Spatial distribution, receptor modelling and risk assessment of organophosphate esters in surface water from the largest freshwater lake in China

The occurrence and risk of organophosphate esters (OPEs) has become a global concern in recent years. This study investigated the occurrence, spatial distribution, and potential sources of thirteen OPEs and their associated ecological and human health risks in water samples from the largest freshwater lake, Poyang Lake, together with its five major inflow rivers and the water channel to Yangtze River. The total OPEs concentrations ranged from 38.44 ng/L to 428.94 ng/L, and the largest tributary Ganjiang River was much more polluted than other rivers. Chlorinated OPEs, such as tris (1–chloro‑2–propyl) phosphate and tri (2-chloroethyl) phosphate occupied the dominant composition of OPEs in the research area. Principal component analysis with multiple linear regression, positive matrix factorization, and correlation analysis were used to apportion the potential sources of OPEs in surface water. The combined contribution of polyvinyl chloride, polyester resins, and polyurethane foam (68.64%), antifoam agent and hydraulic fluids (21.50%), and the release of decorative materials and electric equipment from indoor (9.86%) were identified as the OPEs sources in the study region. The risk quotients (RQs) showed the ecological risk was negligible, but 2-ethylhexyl diphenyl phosphate exposures posed medium ecological risk to aquatic organisms. The carcinogenic and non-carcinogenic risks of the target OPEs were below the theoretical risk threshold values, however, toddlers were much more sensitive to the OPEs exposure in surface water than teenagers and adults. Oral ingestion was the principal exposure pathway, and the health risk via oral ingestion was 1–2 orders of magnitude higher than dermal contact exposure route.

Dynamic proppant-carrying performance of VES-CO2 foam fracturing fluid in the pipeline and the fracture

A viscoelastic surfactant (VES) fluid blends with CO 2 to form the foam fracturing fluid. To obtain the dynamic proppant-carrying behaviors of the VES-CO 2 foam fluid, an experimental system with a horizontal transparent tube and a visual fracture is built. In the horizontal pipeline, it is displayed that the critical settling flow velocity of the ceramsite proppant in the flowing VES-CO 2 foam fluid increases with the temperature. Further, the critical settling flow velocity initially decreases and then increases with both the increases of the foam quality and the proppant ratio, and its transition points are at the foam quality of 0.75–0.80 and at the proppant ratio of 0.25, respectively. In addition, considering the influencing parameters in the experiments, we obtain a correlation equation of the critical settling flow velocity. In the experiments of the fracture observation section, the height of the equilibrium sand bank and the angle of repose are mainly investigated. Both of these two parameters decrease as the foam quality, as well as the injection flow velocity, is increased. Especially, it is found that the angle of repose is below 20° at larger injection flow velocity. • The dynamic proppant-carrying behaviors of the degradable VES-CO 2 foam fracturing fluid are studied. • A correlation equation of the critical settling flow velocity of the proppant-carrying foam fluid is obtained. • The angle of repose in the fracture is generally below 20° at larger flow velocity. • This work provides a reference for the related prediction in the fracturing project.

Experimental investigation of the flow and extinguishment characteristics of gel-stabilized foam used to control coal fire

For understanding the extinguishing effectiveness of gel-stabilized foam fluids, the rheological law, flow characteristics, and extinguishment process were analyzed systematically in this study. The results revealed that gel-stabilized foam was non-Newton fluids, and the foam demonstrated shear-thinning behavior due to the orientation changes in molecular chains and structure destruction of three-dimensional gel at high shear rate. By fitting shear rate-shear stress curves, it was found that power-law equation of pseudoplastic fluid could descript the rheological behavior of foam well, and coefficients of determination for fitting results in all expansion ratios were lager than 0.9950. In addition, a simplified experiment platform of the goaf filled with coals was employed to investigate the flow characteristics of the foam fluids to extinguish coal fire. Analysis showed that gel-stabilized foam presented the hemispherical diffusion shape in porous media, and foam fluids would quickly cover to extinguish the open coal fire with excellent thermal stability. Moreover, the foam fluids also captured the hidden fire source efficiently in porous media by the quick seepage, finally cooling the high-temperature coal fire from 760 °C to 30 °C after injecting foam. The research would provide theoretical guidance for extinguishing coal fire using gel-stabilized foam.

Mechanical evolution of bubble structure and interactive migration behaviors of two particles in flowing wet foam

Multiparticle migration in a wet foam fluid is increasingly found in relevant engineering applications. The microscopic reciprocal influence between the flowing foam and the settling multiparticle has not been fully understood. In this study, we mainly analyze the rheological and mechanical behaviors of this multiphase transport system based on the microscopic structural morphology. The settling behaviors of two particles, as well as the mechanical variation of bubbles influenced by the particles, are mainly explored. We find that the entrance of a bubble into the distance between the two particles positioned vertically causes significantly different bubble pressure components of the drag force for the two particles. In the process of bubble entering the distance, the bubble pressure, as well as the maximum principal stress of the bubble, rises; as the bubble leaves the distance, its pressure and the maximum principal stress decrease. For the two particles positioned horizontally, we mainly analyze the bubble pressure component of the lift force, as well as the pressure evolution of bubbles when the bubble–bubble separation and contact occur in the distance between the particles. This study assists in understanding the microscopic structural and mechanical evolution of wet foam in this multiphase transport system.

Influence mechanisms of several parameters on the interaction between flowing wet foam and settling particle

In practical application, many factors can influence aqueous foam structure. Due to the structural variability of bubble film in a flowing foam system containing a settling particle, the microscopic influence mechanisms of some parameters of both the foam and the particle on the interphase forces are still unclear. In this work, without considering ingredients of the foam fluid, a series of quasi-static multiphase models is built, and the interaction force between the flowing wet foam and the settling particle is firstly investigated at the bubble scale. Then we mainly focus on the parameters, including the foam quality (i.e., gas fraction of a foam), the contact angle between gas-liquid-gas and gas-liquid interfaces and the particle size, and analyze influences of these parameters on the statistical averages of the interphase forces. It shows that both the drag and the lift forces rise with the increase of each of these parameters. More importantly, the foam film and the bubble pressure components of these forces are in detail discussed based on the special structural evolution behaviors of the foam with these different parameters. This study, at the bubble scale, reveals the potential influence mechanisms of these parameters on the interaction between the settling particle and the flowing wet foam.

Non-uniform heat transfer behavior of wet foam fluid in a narrow fracture channel

The heat transfer characteristic of wet foam fluid in some channels has not been fully understood due to its special evolution characteristic. In this study, we explore distribution laws for the temperature and the heat transfer coefficient of the VES-CO2 foam fluid on the heating surface of a narrow fracture channel. The results show that the heat transfer coefficient of foam fluid on the heating surface is affected by multiple factors, such as the foam quality, foam structure, inclined channel and so on. We find that the temperature on the middle part of the heating surface is higher. Especially, due to the drainage of the flowing wet foam, there are different heat transfer characteristics in the middle and at the side of the heating surface. The heat transfer coefficient displays fluctuation behavior at the side of the heating surface. In the inclined channel, the heat transfer coefficient increases with the inclination angle for the positive inclination, and for the lateral inclination, the average cross-sectional heat transfer coefficient decreases with increasing inclination angle. In the low-permeability oil and gas development, this research has important significance for understanding the heat transfer phenomenon of wet foam fluid in formation fracture. It is also expected that this study could provide a reference for related application of wet foam fluid in some special channels.

Rheological and morphological characteristics of foam fluid using hydroxypropyl guar and surfactant

In order to systematically study the rheological and morphological characteristics of foam fracturing fluid, hydroxylpropyl guar (HPG) was selected as the foam stabilizer, sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) were selected as the foaming agents, and foam fracturing fluid used for coalbed methane (CBM) stimulation was prepared. The viscosity, quality and half-life of foam fracturing fluid under different additive concentration levels were tested, and the bubble morphology and its relationship with half-life were observed and quantitatively analyzed with microscopy. In addition, the influence of pulverized coal on foam stability was also studied. The results show that the influence of pulverized coal on the basic parameters of the foam fracturing fluid correlated with the particle size and concentration of the pulverized coal. The small particle size of pulverized coal increased the liquid phase viscosity and half-life of the foam, but reduced the foam quality. With increasing pulverized coal concentration, the effects were enhanced. The average bubble diameter decreased with increasing HPG concentration, and the changing trend of the bubble diameter conformed to the gamma distribution. The foam half-life had a positive and negative correlation with the bubble morphology parameters α and β, respectively. The results can deepen the understanding of the influence of foaming agents, foam stabilizers, and coal particles on the properties of foam fracturing fluids, and provide a reference for the optimization of foam fracturing fluid formulations.

Chemomechanical effects of oxidizer‐CO2 systems upon hydraulically fractured unconventional source rock

AbstractCarbon dioxide (CO2) as supercritical (scCO2) or foamed (CO2‐Foam) fluid has been tested many times as a fracturing fluid, though it has not yet proven viable. Many challenges have been identified with scCO2 as a fracturing fluid, including poor additive solubility, low viscosity, and limited accessibility. However, CO2 is known to adsorb to organic matter (OM) and displace methane (i.e., enhanced coal bed methane [ECBM] operations), or to mobilize oil as in tertiary enhanced oil recovery. In this study we augment the efficacy of the kerogen control fluid (KCF) for stimulating unconventional rock formations by alternating aqueous oxidizing fracturing fluid with CO2 injection or by combining oxidizers directly with CO2 as a new additive. To this end, KCF‐CO2 tests were designed to treat OM and extend the depth of permeability enhancement. We report the first attempt to combine oxidizer with CO2 in the presence of source shale rocks at elevated temperature and pressure. Scanning electron microscopy imaging of the treated shale sample surfaces demonstrate potential porosity and permeability enhancement, though some mineral and organic deposits are also observed, which may prove to be detrimental. Meanwhile, alternating water‐based KCF with CO2 provides a potential improvement to the KCF as predicted by early lab results on OM. The KCF‐CO2 concept has no equivalent to date in unconventional hydraulic fracturing operations. This technology will contribute to reducing the footprint of anthropogenic CO2 and enhancing its permanent sequestration in unconventional stimulated reservoirs, compliant with our global clean energy initiative of carbon capture, utilization, and storage.

Impact responses of an open‐cell natural rubber foam impregnated with shear thickening fluid

AbstractThis research aims to investigate the impact responses of an impact absorbing material prepared from natural rubber (NR). Shear thickening fluid (STF) was developed in order to improve compatibility, and impact response capability of a NR foam. The material was prepared by impregnating NR foam with STF (30 wt% nanosilica with 10 nm). The obtained material is soft under normal circumstances, but immediately stiff when undergoing sudden impact before softening again. The effects of foam densities (0.098, 0.15, 0.24 g/cm3), STF contents (10, 20, 30 vol%), and fluid filling techniques were investigated. Experimental results show that the absorbed force tends to increase by increasing the foam density and the fluid content. Impact absorption capability of the proposed STF (STFA)/NR foam is higher than that of the conventional STF (STF0)/NR foam. In other words, STFA can improve the impact responses of the material providing comparable results with the commercial kneepad, which has the dilatant behavior.

Simply built microfluidics for fast screening of CO2 foam surfactants and foam model parameters estimation

Surfactant-stabilized CO2 foam is a promising technique to increase an oil reservoir’s sweep efficiency and therefore produce more oil. The development of successful CO2 foam formulations requires extensive screening and development of commercially available and new chemicals. In this work, we provide a detailed procedure to build a cost-efficient microfluidic device for rapid prescreening of CO2 foam surfactants. Several surfactant-stabilized CO2 foams were successfully tested using the device which demonstrated complete foam quality testing to pre-screen a surfactant in less than an hour. Foam measurements successfully differentiated between different surfactant solutions and showed an increase of viscosity in comparison to CO2 and brine flood alone. The microfluidic device enabled systematic studies of the effect of chip geometry, surfactant type and concentration, injection flow rate, gas fractional flow, and oil fractional flow on CO2 foam strength. The steady-state foam results from the device were used to estimate the texture implicit foam model parameters. The method provided is not only robust for fast surfactant screening, but also for understanding the foam fluids transport phenomenon and foam modeling using microfluidics.

Laboratory Testing of Fracture Conductivity Damage by Foam-Based Fracturing Fluids in Low Permeability Tight Gas Formations

In the case of fracturing of the reservoirs using fracturing fluids, the size of damage to the proppant conductivity caused by treatment fluids is significant, which greatly influence the effective execution of hydraulic fracturing operations. The fracturing fluid should be characterized by the minimum damage to the conductivity of a fracture filled with proppant. A laboratory research procedure has been developed to study the damage effect caused by foamed and non-foamed fracturing fluids in the fractures filled with proppant material. The paper discusses the results for high quality foamed guar-based linear gels, which is an innovative aspect of the work compared to the non-foamed frac described in most of the studies and simulations. The tests were performed for the fracturing fluid based on a linear polymer (HPG—hydroxypropyl guar, in liquid and powder form). The rheology of nitrogen foamed-based fracturing fluids (FF) with a quality of 70% was investigated. The quartz sand and ceramic light proppant LCP proppant was placed between two Ohio sandstone rock slabs and subjected to a given compressive stress of 4000–6000 psi, at a temperature of 60 °C for 5 h. A significant reduction in damage to the quartz proppant was observed for the foamed fluid compared to that damaged by the 7.5 L/m3 natural polymer-based non-foamed linear fluid. The damage was 72.3% for the non-foamed fluid and 31.5% for the 70% foamed fluid, which are superior to the guar gum non-foamed fracturing fluid system. For tests based on a polymer concentration of 4.88 g/L, the damage to the fracture conductivity by the non-foamed fluid was 64.8%, and 26.3% for the foamed fluid. These results lead to the conclusion that foamed fluids could damage the fracture filled with proppant much less during hydraulic fracturing treatment. At the same time, when using foamed fluids, the viscosity coefficient increases a few times compared to the use of non-foamed fluids, which is necessary for proppant carrying capacities and properly conducted stimulation treatment. The research results can be beneficial for optimizing the type and performance of fracturing fluid for hydraulic fracturing in tight gas formations.

Study on the stability and rheological properties of nitrogen foam under high-pressure condition

After a period of exploitation of carbonate fractured-vuggy reservoir, the water content of oil well keeps increasing, and some wells appear violent water flooding in a short period of time, which leads to the rapid decrease of production. The injection of particle plugging agent is one of the main measures to improve the oil recovery. Foam fluid has the characteristics of low density, high viscosity and low moisture filtration, which can effectively carry plugging particles to the target plugging layers. A stable foam system with high temperature and salinity is optimized and the rheological properties of the foam are studied in this research. The results show that the foam can maintain high viscosity and carry particles effectively even at a higher shear rate.