Residual Oil Research Articles

Study and Application of Fine Dissection Methods for Inter-river Sands in Large Shallow River-controlled Delta Plains

Applying the data of coring wells and logging curves of dense well network, identifying the sedimentary sands of different river systems and contemporaneous periods with the methods of standard layer approximation control and comparison of reference layer combinations, establishing a set of logging phase models of inter-river sands, and using the models as a guideline for micro-phase identification, we have studied the distribution and combination characteristics of the micro-phase sands of the inter-river sand bodies, as well as the type of connectivity with the sand bodies of the river and the relationship, and clarified the distribution characteristics and residual oil distribution of the sand bodies of the inter-river sands. The characteristics of different types of sand body movement and residual oil distribution were clarified, effective dredging methods were proposed, and measures such as oil testing and fracturing were taken, which played an important role in guiding the adjustment and dredging of oil fields in the late stage of high water content.

Molecular insight into oil displacement by CO2 flooding in water-cut dead-end nanopores.

Understanding the mechanisms underlying residual oil displacement by CO2 flooding is essential for CO2-enhanced oil recovery. This study utilizes molecular dynamics (MD) simulations to investigate the displacement of residual oil by CO2 flooding in dead-end nanopores, focusing specifically on the water-blocking effect. The findings reveal that oil displacement does not commence until the water film is breached. The dissolution of CO2 molecules in water and the hydrogen bond interactions between water and rock are the primary factors that disrupt the hydrogen bond network among the water molecules, facilitating the breakthrough of the water film. Additionally, the displacement process can be delineated into four distinct stages - encompassing water film rupture, oil swelling, massive oil displacement, and displacement completion - as evidenced by the oil recovery-displacement time curves. Moreover, a cutting-edge oil recovery-displacement time model precisely quantifies crucial stages in the displacement process. For example, when t < δ, trapped oil is impeded by the water film, while when t > δ + 3τ, displacement culminates successfully. Altogether, this research bolsters comprehension of residual oil displacement in the presence of water blocking and advocates for sustainable oil production strategies in oilfields.

Environmental impacts and decarbonization pathways of oily sludge pyrolysis based on life cycle assessment

Oily sludge is a major hazardous waste generated in the petroleum and petrochemical industry. The increasing accumulation of oily sludge necessitates safe and sustainable management. In recent years, pyrolysis has gained great attention as an effective treatment method for oily sludge. However, a comprehensive environmental assessment of industrial-scale oily sludge pyrolysis remains limited. Based on the life cycle assessment (LCA) method, this study employs data collected from oily sludge treatment plants to investigate the environmental impacts of the whole pyrolysis system, specifically its carbon footprint. The utilization and final disposal of pyrolysis products are in accordance with the real industrial operations. The contributions of each unit process in the pyrolysis treatment of oily sludge to global warming potential (GWP), as well as the decarbonization pathways, are explored in detail. Results indicate that, in general, pyrolysis has lower adverse environmental impacts than incineration does. Within the pyrolysis system, processes such as pyrolysis, flue gas purification, and hot washing are major contributors to GWP. The recycling and utilization of pyrolytic oil and solid residues can significantly mitigate the adverse environmental impacts of oily sludge pyrolysis. Given the combined applications of co-pyrolysis, green electricity, and other low-carbon technologies, the carbon footprint of oily sludge pyrolysis could be reduced from 635.9 to 31.8 kg CO2-eq in the most ideal scenario.

Development of a microbial dewaxing agent using three spore forming bacteria

Microbial enhanced oil recovery (MEOR) is a cost effective and efficient method for recovering residual oil. However, the presence of wax (paraffin) in residual oil can substantially reduce the efficiency of MEOR. Therefore, microbial dewaxing is a critical process in MEOR. In this study, a bacterial dewaxing agent of three spore-forming bacteria was developed. Among these bacteria, Bacillus subtilis GZ6 produced the biosurfactant surfactin. Replacing the promoter of the surfactin synthase gene cluster (srfA), increased the titer of surfactin in this strain from 0.33 g/L to 2.32 g/L. The genetically modified strain produced oil spreading rings with diameters increasing from 3.5 ± 0.1 to 4.1 ± 0.2 cm. The LadA F10L/N133R mutant was created by engineering an alkane monooxygenase (LadA) using site-directed mutagenesis in the Escherichia coli host. Compared to the wild-type enzyme, the resulting mutant exhibited an 11.7-fold increase in catalytic efficiency toward the substrate octadecane. When the mutant (pIMPpladA2mu) was expressed in Geobacillus stearothermophilus GZ178 cells, it exhibited a 2.0-fold increase in octadecane-degrading activity. Cultures of the two modified strains (B. subtilis GZ6 (pg3srfA) and G. stearothermophilus GZ178 (pIMPpladA2mu)) were mixed with the culture of Geobacillus thermodenitrificans GZ156 at a ratio of 5:80:15. The resulting composition increased the rate of wax removal by 35% compared to the composition composed of three native strains. This study successfully developed a multi-strain bacterial agent with enhanced oil wax removal capabilities by genetically engineering two bacterial strains.

Experimental Study on CO2 Flooding Characteristic in Low-Permeability Sandstone Considering the Influence of In-Situ Stress

Summary The pore network controlled by in-situ stress significantly influences the CO2 flooding in low-permeability reservoirs. In this study, the CO2/oil distribution and response of pore structure were monitored online using low-field nuclear magnetic resonance (LF-NMR), and the in-situ stress dependence of oil recovery was analyzed. The results show that the pore structure consists of adsorption pore (AP &amp;lt; 1 millisecond), percolation pore (1 millisecond &amp;lt; PP &amp;lt; 10 milliseconds), and migration pore (10 milliseconds &amp;lt; MP). Oil recovery was primarily influenced by AP and MP at lower in-situ stress, while PP and MP are the main contributors at higher in-situ stress. The matrix experienced compression deformation, microfracture generation, and shrinkage of pore, combined with an increase and followed by a decrease in oil recovery, responding to the increase of in-situ stress from 5 MPa to 15 MPa and from 15 MPa to 20 MPa. The reduction in gas channels promotes a piston-like advancement of oil displacement, resulting in an initial increase in oil recovery, while subsequent decline is linked to heightened pore heterogeneity caused by high in-situ stress. Increased heterogeneity reduces gas displacement stability, hampers CO2 sweep efficiency, and results in a granular distribution of residual oil. The findings provide insight on CO2-enhanced oil recovery (EOR) in low-permeability reservoirs.

Development of surfactant formulation for high-temperature off-shore carbonate reservoirs.

The residual oil left behind after water flooding in petroleum reservoirs can be mobilized by surfactant formulations that yield ultralow interfacial tension (IFT) with oil. However, finding ultralow IFT surfactant formulations is difficult for high-temperature, off-shore, carbonate reservoirs. These reservoirs are often water-flooded with seawater (with a lot of divalent ions), which is often incompatible with many surfactants at high temperatures. The goal of this research is to develop a surfactant formulation for an off-shore carbonate reservoir at 100°C previously flooded by seawater. Surfactant-oil-brine phase behavior was studied for formulations, starting from a single surfactant to mixtures of surfactants and a co-solvent. Mixtures of three surfactants and one co-solvent were needed to produce ultralow IFT formulations for the oil of interest. The surfactant system with polymer mobility control was tested in crushed reservoir rock packs. The cumulative oil recovery was >99% for the surfactant-polymer (SP) flood with an optimal salinity gradient. The constant salinity SP floods with seawater increased oil recovery significantly beyond the water flood (cumulative oil recovery >91%), even though the recovery was lower than that of the optimal salinity gradient SP flood. Our experimental work demonstrates the effectiveness of the surfactant formulation for a high-temperature carbonate reservoir at seawater salinity.

Experimental investigation of capillary pressure diagram in oil/water transition zone of low-permeability reservoirs

The oil/water transition zone, particularly pronounced in low-permeability formations with small pore diameters and high capillary pressure, contains a substantial portion of original oil in place. The capillary pressure curves provide essential data for the calculation of the original oil in place as well as the oilfield development simulation. However, the traditional single capillary pressure curve cannot provide enough information. To address this challenge, an experimental investigation was conducted to explore the capillary pressure diagrams within the oil/water transition zone of low-permeability reservoirs. The results shed light on the complex behavior of capillary pressure, the influence of initial water saturation, and the relationship between initial oil saturation and residual oil saturation. Incorporating the behavior of capillary pressure into reservoir simulation models can enhance reservoir characterization and improve the accuracy of oil production performance in low-permeability reservoirs.

Estimating Residual Oil Saturation in Carbonate Rocks: A Combined Approach of Direct Simulation and Data-Driven Analysis

Summary Estimating residual oil saturation (Sor) post-waterflooding is critical for selecting enhanced oil recovery strategies, further field development, and production prediction. We established a data-driven workflow for evaluating Sor in carbonate samples using microcomputed tomography (μ-CT) images. The two-phase lattice Boltzmann method (LBM) facilitated the flooding simulation on 7,192 μ-CT samples. Petrophysical parameters (features) obtained from pore network modeling (PNM) and feature extraction from μ-CT images were utilized to develop tree-based regression models for predicting Sor. Petrophysical features include porosity, absolute permeability, initial water saturation (Swi), pore size distribution (PSD), throat size distributions (TSD), and surface roughness (Ra) distribution. Our method excludes vugs and macro/nanoporosity, which complicates multiscale simulations—a recognized challenge in modeling carbonate rocks. When subdividing the image into numerous subvolumes, certain subvolumes may contain vugs exceeding the dimensions of the subvolume itself. Hence, these vugs were omitted given the entirety of the image constitutes a vug. Conversely, vugs with dimensions smaller than those of the subvolume were not excluded. Despite scale limitations, our subsampling, supported by substantial data volume, ensures our microscale porosity predictions are statistically reliable, setting a foundation for future studies on vugs and nanoporosity’s impact on simulations. The results show that features obtained from dry-sample images can be used for data-driven Sor prediction. We tested three regression models: gradient boosting (GB), random forest (RF), and extreme gradient boosting (XGBoost). Among these, the optimized GB-based model demonstrated the highest predictive capacity for Sor prediction [R2 = 0.87, mean absolute error (MAE) = 1.87%, mean squared error (MSE) = 0.12%]. Increasing the data set size is anticipated to enhance the models’ ability to capture a broader spectrum of rock properties, thereby improving their prediction accuracy. The proposed predictive modeling framework for estimating Sor in heterogeneous carbonate formations aims to supplement conventional coreflooding tests or serve as a tool for rapid Sor evaluation of the reservoir.

Study on the Mobilization Mechanisms of Microscopic Residual Oil in High-Water-Cut Sandstone Reservoirs

As mature oilfields enter the high-water-cut development stage, significant amounts of residual oil remain trapped underground. To enhance the effectiveness of tertiary oil recovery, it is crucial to understand the distribution and mobilization patterns of this residual oil. In this study, polydimethylsiloxane (PDMS) was used to create a microscopic oil displacement model, which was observed and recorded using a stereomicroscope. The experimental images were extracted, analyzed, and quantitatively evaluated, categorizing the microscopic residual oil in the high-water-cut sandstone reservoirs of Dagang Oilfield into cluster-like, pore surface film-like, corner-like, and slit-like types. Polymer–surfactant composite flooding (abbreviated as SP flooding) effectively mobilized 47.16% of cluster-like residual oil and 43.74% of pore surface film-like residual oil, with some mobilization of corner-like and slit-like residual oil as well. Building on SP flooding, dual-mobility flooding further increased the mobilization of cluster-like residual oil by 12.37% and pore surface film-like residual oil by 3.52%. With the same slug size, dual-mobility flooding can reduce development costs by 16.43%. Overall, dual-mobility flooding offers better development prospects.

The injection pattern investigation of hydrocarbon gas enhanced oil recovery in heterogeneous reservoirs

Considering the large difference in physical properties and low water flooding efficiency of heterogeneous reservoirs, the hydrocarbon gas flooding to enhance oil recovery was investigated. Through the rising bubble apparatus experiment, it was determined that the injected gas and crude oil are immiscible under formation conditions. On the other hand, the displacement experiment carried out on a long core was used to perform the effect of hydrocarbon gas flooding. According to displacement experiment, alternative injection of gas as slugs with water slugs can mobilize the residual oil in place in the reservoirs. When the gas injection rate is 0.5 cm3/min, the recovery efficiency of hydrocarbon gas flooding is highest. At the same time, the lower of water content, the better the timing of waterflooding to gas flooding. In experiments with slugs of different gas–water ratios, when the gas–water ratio is 1:1, the oil recovery efficiency is the highest. The water alternate gas in use within limit adaptation could significantly enhance the residual oil recovery and bring more economic benefits.

Production and Application of a New Biosurfactant for Solubilisation and Mobilisation of Residual Oil from Sand and Seawater

Significant research has been conducted to minimise environmental impacts and promote the sustainable use of resources and raw materials. Microbial surfactants are an example of advanced materials obtained from sustainable production processes. In the present study, a biosurfactant was produced by the yeast Starmerella bombicola ATCC 22214 grown in a previously selected low-cost mineral medium containing 10% sucrose, 1.2% canola oil, and 0.5% corn steep liquor. The biosurfactant reduced surface tension from 72 ± 0.1 to 32.76 ± 0.3 mN/m. The yield was 23 g/L, and the critical micelle concentration was 0.6 g/L. The biosurfactant emulsified 96.25 ± 0.08% of used motor oil, was characterised as a sophorolipid, and exhibited stability under extreme conditions with no significant loss of its properties. Toxicity was assessed by exposing the microcrustacean Artemia salina and the zebrafish (Danio rerio) to the biosurfactant. The biosurfactant proved efficient for use in remediation processes, removing 97.8% and 69.2% of the petroleum derivative from sand in kinetic and static tests, respectively, and removed 91.5% of the contaminant from seawater. The results indicate the potential of this new biosurfactant for the mobilisation and solubilisation of hydrocarbons in the marine environment. This green biomolecule is a promising technology for the replacement of chemical dispersants in the remediation of aquatic and soil systems.

Experimental and Numerical Simulation Study on CO2-Assisted Steamflooding in Ultraheavy Oil Reservoirs

Summary Certain ultraheavy oil reservoirs with depths approaching 1000 m feature wide well spacing. After cyclic steam stimulation (CSS), cold oil zones with high residual oil saturation exist between wells. This leads to a high oil saturation at the steam front during the subsequent steamflooding process, which in turn results in a high injection pressure. The simultaneous injection of CO2 and steam into the formation can optimize formation pressure and enhance steam utilization efficiency. A majority of laboratory-based experimental studies have reported favorable outcomes with CO2-assisted steamflooding. However, some field tests of CO2-assisted steamflooding have encountered severe steam channeling problems, resulting in oil recovery and an oil/steam ratio below the expected level. Consequently, this study uses an ultraheavy oil reservoir as a case study and integrates physical simulation with numerical simulation to investigate the impact of CO2-assisted steamflooding on enhanced oil recovery in ultraheavy oil reservoirs. The findings suggest that the beneficial effect of CO2 in reducing oil viscosity and injection pressure plays a significant role in models with smaller thickness, thereby improving oil production rate and recovery factor. However, as the thickness of the model increases, the adverse effect of CO2 exacerbating steam channeling becomes increasingly evident, leading to a decline in the oil recovery factor and a longer duration to reach the maximum recovery factor. Therefore, in field applications, it is essential to consider adjusting the CO2 injection method or using thermosetting plugging agents to achieve superior results.

The role of nanoparticle–surfactant interactions in air-stabilized foams used for improving oil recovery

Foam flooding, an emerging tertiary oil recovery technique, demonstrates efficacy as a conformance control method in enhanced oil recovery. Conformance control mitigates injected displacement fluid channeling and bypassing, improving macroscopic sweep efficiency. Generated foamed films preferentially enter high permeability zones, diverting subsequent injection into unswept lower permeability regions. Nanoparticle-reinforced foams exhibit consistent bulk stability and effective residual oil mobilization. This work utilizes dynamic foam analysis to probe the synergistic effects of zinc oxide nanoparticles and anionic surfactant on foam generation and persistence. Bulk and local scale foam stability is evaluated under various potassium chloride concentrations. Optimal foam stability occurs near the critical micelle concentration of the surfactant at 2,500 ppm. Increasing electrolyte concentration within a fixed surfactant formulation decreases foam stability due to salt-induced micellar swelling. An optimized electrolyte and nanoparticles with a surfactant combination produce high-quality foam with increased bubble density per unit area. Micellar swelling by nanoparticle adsorption inhibits lamellae thinning and liquid drainage. Enhanced foam properties improve microscopic displacement efficiency and mobility control in foam-assisted oil recovery. Oil recovery is increased by approximately 22% compared to conventional waterflooding.

Molecular Insights into Soaking in Hybrid N2-CO2 Huff-n-Puff: A Case Study of a Single Quartz Nanopore-Hydrocarbon System.

Hybrid N2-CO2 huff-n-puff (HnP) has been experimentally demonstrated to be a promising approach for improving oil recovery from tight/ultratight shale oil reservoirs. Despite this, the detailed soaking process and interaction mechanisms remain unclear. Adopting molecular dynamic simulations, the soaking behavior of hybrid N2-CO2 HnP was investigated at the molecular and atomic levels. Initially, the soaking process of fluid pressure equilibrium after injection pressure decays in a single matrix nanopore connected to a shale oil reservoir is studied. The study revealed that counter-current and cocurrent displacement processes exist during the CO2 and hybrid N2-CO2 soaking, but cocurrent displacement occurs much later than counter-current displacement. Although the total displacement efficiency of the hybrid N2-CO2 soaking system is lower than that of the CO2 soaking system, the cocurrent displacement initiates earlier in the hybrid N2-CO2 soaking system than in the CO2 soaking system. Moreover, the N2 soaking process is characterized by only counter-current displacement. Next, the soaking process of fluid pressure nonequilibrium before the injection pressure decays is investigated. It was discovered that counter-current and cocurrent displacement processes initiate simultaneously during the CO2, N2, and hybrid N2-CO2 soaking process, but cocurrent displacement exerts a dominant influence. During the CO2 soaking process, many hydrocarbon molecules in the nanopore are dissolved in CO2 while simultaneously exhibiting a substantial retention effect in the nanopore. After pure N2 injection, there is a tendency to form a favorable path of N2 through the oil phase. The injection of hybrid CO2-N2 facilitates the most significant cocurrent displacement effect and the reduction in residual oil retained in the nanopore during the soaking process, thus resulting in the best oil recovery. However, the increase rate in total displacement efficiencies of the different soaking systems over time (especially the hybrid N2-CO2 soaking system) was significantly larger before than after injection pressure decays. Additionally, the displacement effect induced by oil volume swelling is significantly restricted before the injection pressure decays compared to the soaking process after the injection pressure decays. This study explains the role of CO2-induced oil swelling and N2-induced elastic energy played by hybrid N2 and CO2 at different stages of the hybrid N2-CO2 soaking process before and after pressure decays and provides theoretical insights for hybrid gas HnP-enhanced recovery. These pore-scale results highlight the importance of injection pressure and medium composition during the soaking process in unconventional oil reservoirs.

THE MECHANICALLY ACTIVATED COMPOSITES BASED ON TUNGSTEN DISULFIDE: SYNTHESIS AND PROPERTIES

In this work, the physicochemical properties of mechano-activated composites (hereinafter referred to as the mechanocomposites) obtained by mechanical activation of commercial tungsten disulfide powder in a planetary mill were studied. Mechanical activation was carried out for 2, 4 and 8 h, but this work presents the results for the last two experiments. The acceleration of the grinding media was controlled through frequency adjustment; a frequency value of 15.5 Hz, according to calculations, corresponds to an acceleration of the grinding media of 50 m/s2 or 5G. The material of the balls from which the grinding balls are made is stainless steel. Due to the relatively low acceleration values, the problem of contamination of the sample with stainless steel components does not occur as a result of surface erosion that occurs when the balls collide with each other and with the walls of the grinding bowl. Mechanical activation was carried out in an inert argon environment, since these were preliminary studies and therefore there was a need to minimize the environmental parameters taken into account. However, the oxidation process will occur during the process of discharging the sample from the grinding bowl of the planetary mill. The resulting mechanocomposites are precursors for the synthesis of monocomponent catalysts for the processing of heavy oil residue. For this purpose, it is necessary to obtain mechanocomposites containing tungsten trioxide and tungsten disulfide. The results of an experimental study of the influence, mainly, of the duration of mechanical activation on the production of tungsten mechanocomposites are presented. The resulting compounds were characterized by X-ray phase analysis (XRD), IR spectroscopy, scanning electron microscopy (SEM), thermogravimetry (TGA) and simultaneous thermal analysis (STA). For citation: Akimov Al.S., Zhirov N.A., Sudarev E.A., Akimov A.S. The mechanically activated composites based on tungsten disulfide: synthesis and properties. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 8. P. 36-43. DOI: 10.6060/ivkkt.20246708.2t.

Advancements in Surfactant Carriers for Enhanced Oil Recovery: Mechanisms, Challenges, and Opportunities.

Enhanced oil recovery (EOR) techniques are crucial for maximizing the extraction of residual oil from mature reservoirs. This review explores the latest advancements in surfactant carriers for EOR, focusing on their mechanisms, challenges, and opportunities. We delve into the role of inorganic nanoparticles, carbon materials, polymers and polymeric surfactants, and supramolecular systems, highlighting their interactions with reservoir rocks and their potential to improve oil recovery rates. The discussion includes the formulation and behavior of nanofluids, the impact of surfactant adsorption on different rock types, and innovative approaches using environmentally friendly materials. Notably, the use of metal oxide nanoparticles, carbon nanotubes, graphene derivatives, and polymeric surfacants and the development of supramolecular complexes for managing surfacant delivery are examined. We address the need for further research to optimize these technologies and overcome current limitations, emphasizing the importance of sustainable and economically viable EOR methods. This review aims to provide a comprehensive understanding of the emerging trends and future directions in surfactant carriers for EOR.

Biodegradation of Spent Oil in Soil Using Citrullus Colocynthis Peels and Other Plant Wastes

Spent oil, which contains hazardous substances that pose health risk to man and his environment, are disposed indiscriminately on land in most mechanic workshops. The waste oil find its way into farmland and water bodies causing contamination of water, plants and lands. The ingestion of contaminated water, plants and animals lead to serious health issues. The abilities of plant wastes such as Citrullus colocynthis peels were investigated for the enhancement of the biodegradation of spent oil in soils. Contaminated soil in microcosms, A to J, were treated with plant wastes, duplicated to give 20 microcosms and incubated for 180 days. Periodic soil sampling from each microcosm was followed by cold extraction with dichloromethane and residual oil were analysed via Gas Chromatography/ Mass Spectrometry techniques (GC/MS). The results showed that the biostimulants accounted for 55.2 % of the total variation in the biodegradation result, P&lt;0.001 at α = 0.05. The compounds identified ranged from C10- C35. The highest molecular weight compounds were 17-Pentatriacontene, 490.93 g/mol and 1-Hexacosene, 490.93 g/mol, while the lowest was p-Menth-8(10)-en-9-ol, cis, 154.25 g/mol. The compounds with the highest and lowest area percentage, 36.04 % and 0.97 % were 9-Octadecenamide, (Z)-, and 9, 9-Dimethyl-9-sila-9,10-dihydrophenanthrene respectively. About, four alkanes, six alkene, fourteen oxygenated, five nitrogen containing- and eight aromatic- compounds were identified after biodegradation. There was no statistical significant difference between the performances of each of the stimulant in the microcosms, P&gt;0.1 at α = 0.05. There was an extremely significant difference between the performance of the stimulated microcosms and the natural attenuation containing NaN3, with P&lt;0.001 at 0.05 significant level. The results show that plant wastes have abilities to enhance the biodegradation of the spent oil. Hence, Citrullus colocynthis peels generated in the Northern Nigeria and other plant waste can be used for cost-effective and safe degradation of spent and crude oil in the Southern Nigeria for the reclamations of lands for agricultural purposes.

Influence of acid and thermal treatment on regeneration of spent bleaching clay and conversion of residual oil to biodiesel

ABSTRACT Spent bleaching clay (SBC) is a hazardous waste produced by vegetable oil refining industries. SBC contains a residual oil (RO) with a lot of organic and inorganic impurities and its disposal leads to severe environmental consequences. In this study, SBC regeneration by extraction, acid modification and pyrolysis under various conditions and biodiesel production were studied. The GC-MS of the extracted RO shows that the fatty acid content is in conformity with crude oil and is appropriate for biodiesel production. FTIR was recorded in order to evaluate the main functional groups of fresh-, spent-, regenerated bleaching clay. The specific surface area (SSA) of fresh bleaching clay (FBC) (166.1 ± 1.7 m2/g) was lower than regenerated bleaching clay (RBC) one. The highest SSA (252.1 ± 1.7 m2/g) was revealed by pyrolysis at 550°C and activation with 10% sulfuric acid. Subsequent increase in the acid concentration and temperature of pyrolysis caused a decrease in the SSA. The heavy metals concentration in RBC was lower than the limits for activated bleaching clay in the National Food Safety Standard. Hence, RBC effectively copes with heavy metal removal. The peroxide, anisidine, acid values and oxidation stability of oil bleached with RBC are comparable to the FBC. Implications: The disposal of spent bleaching clay from vegetable oil refining industries has been recognized as a significant environmental issue. After adsorbing the impurities, spent bleaching clay becomes contaminated with a high concentration of organic and inorganic substances, including residual oils, fatty acids, phospholipids, and potentially toxic heavy metals. This makes spent bleaching clay a hazardous waste and improper disposal can lead to severe environmental consequences. Due to the potential environmental harm caused by spent bleaching clay disposal, it is crucial for vegetable oil refining industries to adopt proper waste management practices. Overall, the proper management and disposal of spent bleaching clay is essential to prevent environmental contamination and safeguard human health.

Study on Surfactant-Polymer Flooding after Polymer Flooding in High-Permeability Heterogeneous Offshore Oilfields: A Case Study of Bohai S Oilfield.

Polymer flooding is an effective development technology to enhance oil recovery, and it has been widely used all over the world. However, after long-term polymer flooding, a large number of oilfields have experienced a sharp decline in reservoir development efficiency. High water cut wells, serious dispersion of residual oil distribution and complex reservoir conditions all bring great challenges to enhance oil recovery. In this study, the method of enhancing oil recovery after polymer flooding was studied by taking the S Oilfield as an example. A surfactant-polymer system suitable for high-permeability heterogeneous oilfields was developed, comprising biogenic surfactants and polymers. Microscopic displacement experiments were conducted using cast thin sections from the S Oilfield, and nuclear magnetic resonance was employed for core displacement experiments. Numerical simulation experiments were also conducted on the S Oilfield. The results show that the enhanced oil recovery mechanism of the surfactant-polymer system is to adjust the flow direction, expand the swept volume, emulsify crude oil and reduce interfacial tension. Surfactant-polymer flooding proves to be effective in improving recovery efficiency, significantly reducing the time of flooding and further enhancing the strong swept area. The nuclear magnetic resonance results indicate a high amplitude of passive utilization of residual oil during the surfactant-polymer flooding stage, highlighting the enormous potential for an increased recovery ratio. Surfactant-polymer flooding emerges as a more suitable technique to enhance oil recovery in the post polymer-flooding stage in high-permeability heterogeneous oilfields.

Numerical simulation of residual oil distribution characteristic of carbonate reservoir after water flooding

Carbonate reservoirs are characterized by abundant reserves and are currently focal points for development in oil and gas producing regions such as the Ahdab oilfield, Tarim Basin, Sichuan Basin, and Ordos Basin. The primary method for exploiting carbonate reservoirs is waterflooding. However, due to the complex pore structure and pronounced heterogeneity of carbonate rocks, the waterflooding process often leads to an unclear distribution of remaining oil and low waterflooding recovery efficiency, significantly impacting the stable and high production of carbonate reservoirs. This paper presents a two-phase flow model of oil and water in distinct pore structures by integrating fluid flow equations and interface tracking equations. It visually represents the waterflooding process at the pore scale, elucidates the distribution and formation mechanism of remaining oil, and discusses the mechanism of microscopic displacement efficiency change. The study reveals that: 1) After waterflooding, the distribution patterns of remaining oil can be categorized into dead-end remaining oil, pressure balance remaining oil, wall-bound remaining oil, Jamin effect remaining oil, and water-encapsulating remaining oil, which are governed by microscopic pore structure, wettability, and preferential flow paths; 2) From the perspective of actual reservoir displacement efficiency, intergranular pores &amp;gt; intergranular dissolved pores &amp;gt; visceral foramen &amp;gt; mould pore, with this trend being more pronounced under hydrophilic wetting conditions; 3) Given the oil-wet to strong oil-wet wettability characteristics of these carbonate rocks, capillary forces pose significant resistance during waterflooding. The conclusion underscores the importance of leveraging the reservoir’s microscopic pore structure and wettability characteristics for actual oil wells, elucidating the evolutionary law of the mechanical mechanism of oil-water interface advancement, clarifying oil-water percolation characteristics at the pore scale, and understanding the microscopic displacement physical mechanism, all of which are crucial for guiding the design of schemes aimed at enhancing reservoir recovery efficiency.