Permeability Oil Research Articles

Biodegradable rice bran insoluble dietary fiber-chitosan blend films: Characterization and potential applications

A composite film of insoluble dietary fiber (IDF) from rice bran (RB) blended with chitosan (IDF-CS film) was prepared and characterized. The thermal stability, thickness, tensile strength, colour, water vapour permeability (WVP) and oil permeability (PO) of the film were analysed. SEM micrographs revealed the porous morphology of the film. XRD spectra suggested an amorphous crystalline nature of the film. FTIR spectra showed a 1600 cm−1 peak in chitosan and dietary fiber, indicating C=O stretching, and TGA showed good thermal stability under various temperatures. The thickness increased to 0.104 mm in the film containing IDF -Chitosan2:2. The tensile strength (TS) was enhanced to 18.420 MPa in the film containing IDF -Chitosan2:2. The elongation at break (EB) was higher (12.65%) in films containing low concentrations of IDF-Chitosan0.5:0.5. WVP was enhanced to 5.856 ×10-12 g·cm/cm2·Pa·s in the film containing IDF 2:2. The prepared film showed excellent soil-degrading properties, with a degradation rate of 96% after 15 days. The IDF-CS film demonstrated a substantial inhibitory potential against Gram-positive bacteria. The scavenging capacities of the degradable film were 96.5% for DPPH and 98.8% for ABTS. Moreover, the viability of cervical HeLa cell line was 10% at 200 μg/ml compared with that of the positive control (4%). Significant cytomorphological changes leading to necrosis in treated cells were observed using light and fluorescence microscopy. The film (IDF-CS) developed is environmentally friendly and could be used as a novel therapeutic material for treating bacterial pathogens, scavenging free radicals, and inhibiting cancer cell proliferation.

Microemulsion for stimulating wells with high gas and water cut

This article is the first to suggest that microemulsions can also be used to reduce gas and water saturation in the reservoir in the process of well stimulation. This article presents the results of an experimental study on the possibility of using a multifunctional microemulsion for well stimulation at a bottomhole pressure below the saturation pressure and high water cut. It has been found that the treatment of the bottomhole zone with the developed microemulsion leads to a significant reduction in the size of gas bubbles due to a decrease in interfacial tension, which facilitates their removal from the bottomhole zone and increases hydraulic diffusivity of the porous medium for oil approximately five times. In addition, adsorption of the composition on the pore walls, changes the wettability of the walls from oil-wet to the water-wet providing a sliding surface for the oil. The increase in phase permeability for oil, which is proportional to the hydraulic diffusivity and the wettability alteration enhance the oil flow rate by 13.5% and consequently oil recovery by 21%. In order to visualize the effect of microemulsion the simulation of oil flow through porous media was performed using COMSOL Multiphysics.

Formulation and development of topical nano-emulgel TDDS for delivering Vitex Negundo as a painkiller: Enhancing effectiveness with natural essential oil permeation promoters in an innovative drug delivery system for rheumatoid arthritis treatment—A NDDS

Formulation and development of topical nano-emulgel TDDS for delivering Vitex Negundo as a painkiller: Enhancing effectiveness with natural essential oil permeation promoters in an innovative drug delivery system for rheumatoid arthritis treatment—A NDDS

Freestanding measurement of the polar/nonpolar adsorption interface for complete hydrophobicity switching in polyethylene nanofibrous membranes by trace poly(acrylic acid)

This study explores the underlying mechanisms of polar/nonpolar adsorption dynamics utilizing ultrathin polyethylene (PE) membranes, presenting an innovative method to directly characterize interfacial phenomena. By modifying the surface of these membranes with trace amounts of poly (acrylic acid) (PAA), we probe the entropy-driven hydrophobic and depletion interactions that dominate the adsorption process. This encapsulation significantly alters the hydrophilicity of PE—from a contact angle of 132.2° to 37.0°—while maintaining the micro-structural integrity at remarkably low PAA loadings. For the first time, this approach allows for the isolation and direct characterization of the interface through methods such as weighing, thermal cycling, and tensile testing. Key findings demonstrate that the adsorbed PAA layer is exceptionally loosely packed, exhibiting a porosity exceeding 90 %. Moreover, the presence of PAA differentially impacts the crystallization behavior of FCC and ECC within PE, hindering FCC crystallization significantly while mildly affecting ECC. Post-adsorption, the modified PE membrane exhibits smart separation capabilities: it behaves amphiphilically in air, allowing simultaneous permeation of water and oil, and selectively separates water/oil mixtures in liquid environments based on the pre-wetting phase. The resulting hydrophilic ultrathin PAA-PE membranes maintain high transparency (over 90 %), robust mechanical strength (309 MPa in tensile maximum stress), and substantial porosity, all within a freestanding, 340 nm-thick form. This work not only elucidates several first-time observations of the intriguing polar/nonpolar adsorption interface but also provides new approaches for thorough and stable physical modification to polymer membranes.

A desert beetle-like mesh membrane by decorating superhydrophilic Fe-doped Cu-MOFs onto superhydrophobic CuC2O4 bowknot-like arrays for boosting water-in-oil emulsion separation

Inspired by the water-collecting mechanism of the back structure of the Stenocara beetle, a novel hierarchical structured mesh membrane was rationally constructed by decorating superhydrophilic Fe-doped Cu-MOFs (HKUST-1) onto superhydrophobic CuC2O4 bowknot-like arrays for enhanced separation of oil-in-water emulsions. The Fe-doped HKUST-1 particles, which accumulated in the mesh pores of the superhydrophobic membrane, served as “water-adsorption” centers to facilitate the capture, aggregation, and adsorption of tiny emulsified water droplets. Moreover, the tight packing of Fe-doped HKUST-1 particles within mesh pores not only significantly reduced the pore size, but also extended the effective range of HKUST-1 particles, thereby enhance the “capture-aggregation” process for emulsified water droplets in oil phases. This rationally-designed mesh membrane was demonstrated to efficiently separate water-in-oil emulsions prepared with different oil types, achieving the highest oil permeation flux of approximately 1200 L·m−2·h−1 and maintaining a water content in the oil phase below 57.0 mg·L−1. This study not only presents a simple and scalable strategy for developing a biomimetic anisotropic superwetting mesh membrane, but also underscores its potential industrial applications in oily wastewater treatment.

Experimental Investigation on the Evolution of Physicochemical Properties and Dissolution Mechanism of High-Siliceous Shale with Acid Treatment

Summary The investigation of the influence of acidification conditions on the modification patterns of shale and the mechanisms of shale acidification processes is an indispensable aspect of further development within the field of shale acidizing theory. Prior research on shale acidizing has predominantly used hydrochloric acid (HCl) and carbonate-rich shale, which has restricted the scope of application for shale acidizing techniques and has not thoroughly examined the reaction kinetics of acid-rock interactions under reservoir conditions. This study focuses on siliceous shale, utilizing hydrogen fluoride (HF) in rotating disk experiments to assess the kinetic parameters of acid-rock reactions under varying acidification conditions, including duration, concentration, temperature, bedding direction, and acid flow velocity. Key influencing factors such as time, temperature, concentration, and experimental methods were selected for a comprehensive analysis, incorporating mineral composition [X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS)], microstructure (SEM), pore medium characteristics [mercury intrusion porosimetry (MIP) and low-temperature nitrogen adsorption (LNA)], surface morphology (3D laser scanning), and nanoindentation testing (NIT). The findings confirm the positive role of acid treatment in enhancing the permeability of shale oil and gas and in softening the reservoir rock, while also indicating potential negative impacts on hydrocarbon extraction, such as the formation of precipitated byproducts and the exfoliation of rock layers. This paper investigates the patterns of influence of HF acidizing parameters on siliceous shale and elucidates the mechanisms of action in shale acidification transformations, thereby providing a theoretical foundation for the modification of shale oil and gas reservoirs.

Microscopic Remaining Oil Classification Method and Utilization Based on Kinetic Mechanism

In reality, the remaining oil in the ultra-high water cut period is highly dispersed, so a thorough investigation is required to understand the microscopic remaining oil. This will directly influence the technological direction and allow for countermeasures such as enhanced oil recovery (EOR). Therefore, this study aims to investigate the state, classification method and utilization mechanism of the microscopic remaining oil in the late period of the ultra-high water cut. To achieve this, the classification of microscopic remaining oil based on mechanical mechanism was developed using displacement CT scan and micro-scale flow simulation methods. Three carefully selected mechanical characterization parameters were used: oil–water connectivity, oil–mass specific surface and oil–water area ratio. These give five types of microscopic remaining oil, which are as follows: A (capillary and viscous oil cluster type), B (capillary and viscous oil drop type), C (viscous oil film type), D (capillary force control throat type), and E (viscous control blind end type). The state of the microscopic remaining oil in classified oil reservoirs was defined after high-expansion water erosion. Based on micro-flow simulation and analysis of different forces during the displacement process, the main microscopic remaining oil recognized is in class-I, class-II and class-III reservoirs. Within the Eastern sandstone oilfields in China, the ultra-high water-cut stage is a good indicator that the class-I oil layer is dominated by capillary and viscous oil drop types distributed in large connected holes. The class-II oil layer has capillary and viscous force-controlled clusters distributed in small and medium pores with high connectivity. In the case of the class-III oil layer, it enjoys the support of capillary force control throats that are mainly distributed in small holes with high connectivity. Integrating mechanisms of different types of micro-remaining oil indicates that, enhancing utilization conditions requires increasing pressure gradient and shear force while reducing capillary resistance. An effective way to improve the remaining oil utilization is to increase the pressure gradient and change the flow direction during the water-drive development process. Hence, this forms a theoretical basis and a guide for the potential exploitation of remaining oil. Likewise, it provides a strategy for optimizing enhanced oil recovery in the ultra-high water-cut stage of mid-high permeability oil reservoirs worldwide.

Sodium Alginate–Montmorillonite Composite Film Coatings for Strawberry Preservation

In this study, we prepared sodium alginate (SA) and montmorillonite (MMT) composite films for application in coatings for strawberry preservation. SA and MMT were used as the matrix and glycerol was used as a plasticizer. Six types of composite films with different MMT contents were compared by analyzing their mechanical properties, permeability, and preservation effects. The results show that the mechanical properties of the 10 and 20% MMT composite films were superior, with tensile strength and fracture elongation values reaching 63.09 and 48.06 MPa and 5.75 and 6.47%, respectively. Increased MMT content caused the water vapor permeability to decrease, while the effect on oil permeability was the opposite. A comparison of the preservation effect provided by the coatings showed that, on day 12, the weight loss, malondialdehyde content, and respiratory intensity of strawberries treated with the 20% MMT coating liquid decreased by 43.3, 25.8, and 57.1%, respectively, compared with the control. The contents of titratable acid, soluble sugar, total phenols, and soluble solids decreased by 25.8, 37.7, 25.9, and 14.5%, respectively. The results provide data support for the application of these new composite films as edible coatings for fruit preservation.

Analytical prediction model for edge water invasion flow rate in SAGD heavy oil reservoirs

SAGD (Steam Assisted Gravity Drainage) technology is a highly developed method for the extracting heavy oil. In the Liaohe Oilfield in China, there are 72 SAGD well groups within a massive heavy oil reservoir containing edge water and the risk associated with edge water invasion is substantial. Currently, the injected steam is less than 50 m away from the edge water, which increases the urgency to address the potential invasion of edge water. If the edge water flows into the reservoir, it will impact nearly 8.0 × 105 tons of crude oil production. Recognizing the importance of mitigating the edge water invasion, this paper proposes a prediction model for the edge water invasion flow rate in SAGD reservoirs. The model integrates mass and heat transfer dynamics between the steam chamber and edge water, the relative permeabilities of oil and water phases, and the viscosity-temperature relationship of water. The model is validated through numerical simulations and field data. The findings indicate that for SAGD reservoirs with a permeability greater than 1 D, maintaining a minimum distance of 25 m between the edge water and the steam chamber is advisable, especially when the pressure differential is 0.5 MPa. Furthermore, the prediction model is used to forecast the edge water breakthrough time and evaluate water invasion risk. A prediction chart for the edge water invasion flow rate is developed, providing a practical tool for estimating invasion flow rate curves. Also, a method of edge water invasion warning is established, with a corresponding chart that offers a quick assessment of water invasion risks in heavy oil reservoirs. Overall, this research lays a foundational framework for understanding and managing the edge water invasion in SAGD operations, offering critical insights for the future study aimed at addressing the challenge posed by edge water in heavy oil reservoirs.

Study on characteristics, efficiency, and variations of water flooding in different stages for low permeability oil sandstone

AbstractWater flooding is an important way to improve recovery in low‐permeability sandstone oil reservoirs. How to decouple the water flooding process using dynamic and static information is a hot topic. In this paper, taking the Paleocene low‐permeability oil sandstone, BY area, eastern Nanxiang Basin as an example, the microscopic water flooding process in the low‐permeability sandstone matrix was systematically investigated, and the characteristics of water channeling under the conditions of fracture existence were analyzed using the dynamic and static monitoring data. The results show that the target layer mainly develops frequently thin stacked composite sand bodies. Under the combined influence of matrix and fracture seepage, the low‐permeability sandstone developed by water flooding shows that there is a single direction of efficiency. The direction of advantageous water advancement is 45° north–east, and the speed of water flooding advancement is 2.57 m/day. Microscopic water‐drive oil experiments show that bound water is mainly distributed in the original low‐permeability sandstone as a membrane in the pore wall and as short rods in the throat. Differences in pore structure and petrophysical properties affect the residual oil content and degree of oil recovery. For sandstones with good petrophysical properties, mild water flooding can improve crude oil recovery. The increase in oil production is mainly concentrated in the early stage of water flooding development, and the increase in oil recovery degree is not significant with the increase in injection multiples in the middle and late stages. However, for sandstones with relatively poor petrophysical properties, water flooding is more effective in the early and late stages than in the middle stages. Therefore, it is necessary to adjust the water flooding measures according to the differences in the petrophysical properties of the sand body. Local tectonics and natural fracture strikes are important factors affecting the direction of the expansion of water flooding fractures. Overall, the prevention of water channeling in low‐permeability sandstones has to take into account the complex coupling between water flooding fractures, natural fractures, and hydraulic fractures.

Mechanism recognition and application effect analysis of air injection development in ultra-low permeability oil reservoirs

Abstract There are few application examples of air drive development technology in ultra-low permeability oil reservoirs in China. The article relies on the air drive development block of H oilfield, and based on the results of core start-up pressure gradient experiment, relative permeability experiment, gas composition experiment, and gas swelling experiment, conducts research and analysis on the seepage mechanism and low-temperature oxidation mechanism of air drive development, demonstrating the advantages of air drive development in oil displacement mechanism of ultra-low permeability oilfield. Based on the basic parameters of oil fields developed by air flooding both domestically and internationally, the specific blocks suitable for air flooding development in H oilfield are selected. The feasibility of conducting air flooding development in low permeability oil fields is demonstrated from three aspects: indoor real core experimental data, safety, and the maturity of existing equipment and technology. At the same time, an analysis is conducted on the development status of the air drive block in H oilfield. By comparing the development effects with adjacent water injection blocks, it is demonstrated that the air drive development effect in ultra-low permeability oilfield is superior to water injection development.

The application of PVC hollow fiber ultrafiltration membrane in ultra-low permeability oilfield

Abstract Oil containing wastewater produced from ultra-low permeability oil fields generally needs to be treated to meet the 5-1-1 standard before it can be reinjected. In order to meet the standards for treating oily wastewater in ultra-low permeability oil fields, PVC hollow fiber ultrafiltration membranes and pre-treatment processes for removing oil, suspended solids, sulfides, etc. before the membrane were selected. The application shows that the aeration air flotation flow sand filtration PVC hollow fiber ultrafiltration membrane process can treat oily wastewater, and the treated water can reach the “5-1-1” standard. In the pre-treatment process of PVC hollow fiber ultrafiltration membrane, the silicone rubber membrane aeration device has good oxidation effect, high efficiency in micro nano air flotation for oil removal and suspended solids, and easy management of sand flow filters. This process has economic feasibility and provides technical support for the treatment of oily wastewater in ultra-low permeability oil fields, with great promotional value.

Experimental Study on the Treatment of Produced Water from Carbon Dioxide Drive by Aeration Method

Abstract To further explore the effective development of produced water treatment technologies suitable for low to ultra-low permeability oil fields, and to clarify the water quality characteristics of produced water from CO2 flooding. A study was conducted on the basic water quality characteristics of produced water from low to ultra-low permeability oil fields. Indoor CO2 gas removal experiments were conducted using the aeration method under 40°C atmospheric pressure conditions. The research results indicate that the CO2 content in the extracted water is one of the important influencing factors for the changes in characteristic parameters such as water pH, mineralization, and corrosion rate; Under the condition of 40°C atmospheric pressure test, the aeration method has a significant treatment effect on the produced water from CO2 flooding, which can effectively remove 70% of the CO2 in the water, thereby improving the pH of the water to 8, and effectively inhibiting the corrosion rate of the produced water below 0.076mm/a.

Bioinspired surface silicification of cellulose-mediated PVDF membranes for significantly enhancing superhydrophilicity and anti-oil adhesion toward ultrafast oil/water emulsion separation

Cellulose is a widely used hydrophilic material due to its rich hydrophilic hydroxyl groups. However, the presence of its lipophilic segment will affect the antifouling performance. Finding strategies to improve this problem has attracted considerable attention. In this work, a layer of silica was applied to a cellulose-deposited polyvinylidene fluoride membrane through a straightforward in-situ bionic silicification process of tetraethyl orthosilicate. The contact angle and oil droplet contact test proved that the high-hydrophilicity and underwater superoleophobicity of the silicified membranes were significantly enhanced. The surface structure and composition were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results of show that this improvement was mainly attributed to the presence of silicon hydroxyl groups, buried cellulose chains, and micro-nanostructures composed of cellulose and silica. The stable silica coating also provided protection for the polymeric membrane against degradation after water washing for 24 h, ultrasonic treatment (40 KHZ) for 10 min or exposure to different pH levels (pH=1, 4, 9 and 12) and saturated sodium chloride solution for 24 h. Furthermore, the silicified membrane showed outstanding oil adhesion resistance and permeation flux, enabling effective purification of different oil-in-water emulsions that were stabilized by emulsifiers. Notably, the membrane achieved a high oil removal rate (> 99.4 %) of various emulsions (toluene-in-water, cyclohexane-in-water, tetrachloroethane-in-water, soybean oil-in-water, toluene-in-salt solution, toluene-in-acid solution and toluene-in-alkaline solution emulsions). In particular, for toluene-in-water emulsions (oil droplets in the emulsion ranged from 58.77 nm to 615.1 nm), a significantly enhanced permeation flux (4777 L·m−2·h−1·bar−1) was obtained at 0.8 bar pressure. Even after multiple cycles of separation, the flux was higher than that of the unsilicified membrane. Overall, this approach is mild, simple, efficient, and easily scalable, making it an ideal method for producing superhydrophilic coatings with substantial application potential.

Predicting and optimizing CO2 foam performance for enhanced oil recovery: A machine learning approach to foam formulation focusing on apparent viscosity and interfacial tension

Carbon dioxide foam injection stands as a promising method for enhanced oil recovery (EOR) and carbon sequestration. However, accurately predicting its efficiency amidst varying operational conditions and reservoir parameters remains a significant challenge for conventional modeling techniques. This study explores the application of machine learning (ML) methodologies to develop a robust model for matching experimental values in CO2 foam flooding scenarios. Leveraging a comprehensive dataset encompassing diverse surfactants and rock types, with varied porosity and permeability, our model demonstrates accurate predictions across a wide spectrum of conditions. By focusing on key parameters such as foam apparent viscosity, interfacial tension (IFT), injected foam volume, initial oil saturation, porosity, and permeability, we unveil the pivotal role of these factors in determining CO2 foam EOR performance. Through rigorous analysis, we identify the relative importance of each input parameter, with injected foam volume, apparent viscosity, and IFT emerging as dominant factors. The most accurate model was deep neural network (DNN) (R2 value of 0.99). Higher foam viscosity and lower IFT were found to significantly enhance oil recovery rates, though their effects plateau beyond certain thresholds (apparent viscosities above 1200 cP and IFT values below 0.2 mN/m). The findings underscore the potential of ML-driven approaches in enhancing CO2 foam EOR predictions, offering insights crucial for optimizing foam flooding performance across diverse reservoir settings.

Unveiling the potential of confocal raman spectroscopy in the analysis of oil permeation in human hair fibers

Unveiling the potential of confocal raman spectroscopy in the analysis of oil permeation in human hair fibers

The Time-Varying Characteristics of Relative Permeability in Oil Reservoirs with Gas Injection

Relative permeability is a critical parameter in reservoir numerical simulation and production prediction, intimately associated with reservoir architecture and fluid property. During gas injection development, substantial alterations in reservoir properties and fluid phase behavior induce dynamic changes in relative permeability. Clearly characterizing the time-varying features of relative permeability is very useful for an understanding of how gas injection influences fluid mobility within the reservoir and enhances recovery rates. In this paper, core displacement experiments are firstly conducted to obtain the characteristics of the relative permeability of oil and gas under various development stages and displacement conditions, further delineating the comprehensive shifts in reservoir properties at different gas injection stages. Subsequently, a novel reservoir numerical simulation method is proposed that considers the spatial and temporal segmentation of relative permeability curves in the reservoir simulation. Finally, a practical application is presented to clarify the effects of injection and production parameters on the development performance of gas flooding oil reservoirs. The results show the following: (i) Significant time-varying characteristics of relative permeability occur throughout gas injection development, in the early stages of gas injection, where most of the reservoir is at the gas injection front, and a rightward shift in relative oil and gas permeability indicates that gas injection promotes oil mobility. Conversely, in the later stages of gas injection, as the reservoir reaches the trailing edge of gas injection, the change trend in relative oil and gas permeability reverses, shifting leftward, thereby exacerbating the gas breakout phenomena. (ii) Increasing the rate of gas injection causes relative oil and gas permeability to move leftward, effectively enhancing the gas volume sweep coefficient and microscopic oil displacement efficiency at lower injection speeds while reducing development performance at higher injection speeds. (iii) An increase in gas injection pressure causes relative oil and gas permeability to shift rightward, and although it reduces residual oil saturation and enhances microscopic oil displacement efficiency, it also intensifies gas breakout phenomena and lowers the gas volume sweep coefficient. This paper provides theoretical guidance and technical support for the design of gas injection strategies, optimization of injection and production parameters, and production forecasting.

Shock wave generated by composite energetic material driven by electrical non-penetrating wire explosion plasma.

Underwater shock wave technology can realize dynamic rock fracture, which is helpful to increase oil and gas reservoir permeability. It can realize the efficient exploitation of medium and low maturity oil and gas resources. In practical application, the shock wave parameters require not only high intensity but also safety and controllability. To meet these requirements, insensitive composite energetic materials driven by electrical wire explosion plasma were proposed, which is one of the most promising methods. However, when in use, the load assembly process containing wires and energetic materials is complex. In this paper, a new type of energetic material load is proposed, using non-penetrating wire to drive composite energetic material. It can simplify the production process of the energetic load and produce acceptable shock wave parameters. The test results show that both the energy deposition of the wire and the shock wave intensity decrease under a non-penetrating wire structure. However, the shock wave intensity is still higher than that of the underwater electrical wire explosion. Based on schlieren diagnosis, it is found that the composite energetic material is gradually driven, and the energy release is not concentrated. In addition, the "non-wire" structure driving condition was discussed in contrast. Under this condition, the process of ionization channel establishment in composite energetic materials is random. The shock wave intensity is weak because the composite energetic material is in the process of slow detonation.

Investigation on the oil permeation–adsorption–diffusion combined action mechanism of the adsorbed layer for flexible oil storage in waters

A novel method entitled flexible oil storage in waters is proposed, aiming to address the limitations of current oil storage systems and enhance the country's oil storage capacity. However, oil contamination severely restricts its applicability. To ensure the environmental sustainability of the method, the adsorbed layer is added outside the oil bladder, and the study investigates the material and the action mechanism of the adsorbed layer for flexible oil storage in waters. The results show that, with long breakthrough time and low oil concentration as criteria, the reed straw biochar is more suitable as the adsorbed layer filling material compared to the coconut shell and the apricot shell biochar and the fluorinated ethylene propylene copolymer is more suitable as the adsorbed layer membrane material compared to polyvinyl chloride. The adsorbed layer action mechanism involves multiple interactions, including permeation, adsorption, accumulation, and diffusion. They are coupled and together influence the adsorption effect. The empirical formula for the adsorbed layer's lifespan is derived, which helps in designing the adsorbed layer to satisfy specific lifespan requirements. This study provides theoretical and engineering guidance for the application of flexible oil storage in waters, contributing to the development of oil storage techniques.

Analysis of asynchronous/inter-fracture injection-production mechanism under the condition of five-spot vertical and horizontal well combination in low permeability oil reservoirs

At present, low permeability resources are the focus of the development of petroleum industry. In this paper, firstly, the oil displacement mechanism under the condition of vertical and horizontal well combination is clarified. Secondly, the difference of the mechanism of enhancing oil recovery between asynchronous and inter-fracture injection and production is revealed. Thirdly, the difference of energy supplement mechanism between huff and puff and displacement is compared and analyzed. Results show that: (a) with asynchronous injection-production development, the oil saturation drop around the water injection well is greater than that of periodic injection-production and synchronous injection-production. (b) Under the dual effects of water injection pressure difference and capillary force, part of the injected water enters the reservoir with relatively small pore channels, expanding the swept volume. (c) In the soak stage of asynchronous injection-production development, capillary force is the main control factor of oil-water permeability, and its size determines the permeability level. (d) The injected water first flows through the large channel and then flows into small channel to complete the imbibition and replacement. (e) The flow field of asynchronous injection-production has a large sweep range, which is conducive to improving oil recovery.