Oil Recovery Applications Research Articles

Synergistic Effect of Opuntia ficus-indica Cladode mucilage on Physicochemical and Rheological properties of HPAM polymer solutions for EOR Application

This study focuses on the synthesis of a series of mixtures of a partially hydrolyzed polyacrylamide (HPAM), noted (H), and a cladode Opuntia ficus-indica mucilage (M). The main objective is to minimize the exclusive dependence of HPAM in the field of tertiary oil recovery, specifically in the process known as EOR.This study showed that a combination of 20% mucilage and 80% HPAM, for a total concentration of 800 ppm in solution, gives rheological performance equivalent to a solution of HPAM alone at 6000 ppm. The resulting mixture which is characterized by viscoelastic liquid behavior, exhibits remarkable flow and elasticity properties.This characteristic is considered favorable for extracting trapped oils from pores under effect of the normal stress. Spectral analysis revealed the presence of silica groups in the mixture, elements widely used in researchers in association with HPAM. Thermogravimetric analysis (TGA) demonstrated that mucilage decomposition only occurs at temperatures above 200 °C. As the main conclusion, all the physicochemical and rheological data argue in favor of the integration of mucilage in HPAM in order to minimize its concentration in Enhanced Oil Recovery (EOR) applications.

Understanding the Factors Affecting the Adsorption of Surface-Active Agents onto Reservoir Rock in Chemical Enhanced Oil Recovery Applications: A Comprehensive Review

Understanding the Factors Affecting the Adsorption of Surface-Active Agents onto Reservoir Rock in Chemical Enhanced Oil Recovery Applications: A Comprehensive Review

Superhydrophobic Co-MOF-based sponge for efficient oil-water separation utilizing photothermal effect

Effectively addressing crude oil spills remains a global challenge due to its high viscosity and limited flow characteristics. In this study, we successfully prepared a modified sponge (PCP@MS) by embedding the photothermal material of Co-HHTP and coating the melamine sponge (MS) with low-surface-energy polydimethylsiloxane (PDMS). The PCP@MS exhibited outstanding hydrophobicity with WCA of 160.2° and high oil absorption capacity of 59–107 g/g. The PCP@MS showed high separation efficiency of 99.2% for various oil-water mixtures, along with notable self-cleaning properties and mechanical stability. The internal micro-nano hierarchical structure on the sponge surface significantly enhanced light absorption, synergizing with the photo-thermal conversion properties of Co-HHTP, enabled PCP@MS to achieve a surface temperature of 109.2 °C under 1.0 solar light within 300 s. With the aid of solar radiation, PCP@MS is able to heat up quickly and successfully lowering the viscosity of the surrounding crude oil, resulting in an oil recovery rate of 8.76 g/min. Density functional theory (DFT) calculation results revealed that Co-HHTP featured a zero-gap band structure, rendering advantageous electronic properties for full-wavelength light absorption. This in situ solar-heated absorbent design is poised to advance the practical application of viscous oil spill cleanup and recovery.

Rheological behavior of hydrophobic association polyacrylamides with high salt resistance and corrosion inhibition: Cross-linking modification based on trace dopamine hydrochloride derivatives

Hydrophobic association polyacrylamides (HAPAMs) have great potential for use in polymer flooding because of their unique aggregative, hygroscopic, and other compatible properties; however, their poor solubility in high-salt reservoir environments is one of the drawbacks of current polymers for enhanced oil recovery (EOR) applications. Herein, an amphipathic hydrophobic monomer (hexadecyldimethylallyl ammonium chloride, DMAAC16) and a dopamine hydrochloride-derived monomer (DAAM) were successfully introduced into HAPAM to synthesize novel dopamine hydrochloride-modified hydrophobic association polymers (HAPAMC16D). As a result, HAPAMC16D exhibited not only good comprehensive properties based on its porous network structure but also excellent viscosity due to the presence of the DAAM monomer. When the concentration of the polymer solution was greater than the critical association concentration (CAC), the apparent viscosity reached 614 mPa s at 5 g/L C16D5. Importantly, the salt resistance increased significantly in the representative sodium and calcium ion tests, which was attributed to the degree of chemical cross-linking and the intermolecular hydrophobic bonding force. The temperature and salt resistance tests simulating different environments for EOR showed that C16D4 had an apparent viscosity of 158 mPa s, a retention rate of 28.52 % at 90 °C and a total dissolved solids (TDS) greater than 30,000. Additionally, the weight loss method and electrochemical experiments indicated that the highly salt-resistant hydrophobic association polymers had favorable corrosion inhibition effects, with an inhibition efficiency of up to 99.02 % in the 1 M hydrochloric acid-Q235 carbon steel system. This hydrophobic association strategy provides a new approach for designing highly salt-resistant materials for polymer flooding in harsh reservoir environments.

Investigating the Potential of a Transparent Xanthan Polymer for Enhanced Oil Recovery: A Comprehensive Study on Properties and Application Efficacy

This study delves into the properties and behavior of xanthan TNCS-ST, a specialized variant designed for enhanced oil recovery (EOR) purposes. A notable aspect of this polymer is its transparency and capability to dissolve in high salt concentrations, notably up to 18% total dissolved solids. Various laboratory methods are employed to assess the polymer’s distinctive traits, including transparency, salt tolerance, and high pyruvylation. These methods encompass preparing xanthan solutions, conducting filtration tests, assessing energy consumption, and measuring rheological properties. The findings highlight the influence of salt concentration on xanthan’s filterability, indicating increased energy requirements for dissolution with higher salt and xanthan concentrations. Additionally, this study observes temperature-dependent viscosity behavior in different solutions and evaluates the shear stability of xanthan. A significant and novel characteristic of TNCS-ST is its high salt tolerance, enabling complete dissolution at elevated salt concentrations, thus facilitating the filterability of the xanthan solution with sufficient time and energy input. Core flooding experiments investigate fluid dynamics within porous rock formations, particularly sandstone and carbonate rocks, while varying salinity. The results underscore the substantial potential of the new xanthan polymer, demonstrating its ability to enhance oil recovery in sandstone and carbonate rock formations significantly. Remarkably, the study achieves a noteworthy 67% incremental recovery in carbonate rock under the high salinity level tested, suggesting promising prospects for advancing enhanced oil recovery applications.

Development and performance evaluation of nonionic surfactant-stabilized nanoemulsion for enhanced oil recovery applications in tight reservoir

Nanoemulsions have garnered great attention as a chemical additive for enhanced oil recovery (EOR) technology worldwide due to their small size and unique physicochemical properties. Herein, this work introduces a novel nonionic surfactant-stabilized nanoemulsion prepared using a low-energy method for EOR projects in the Chang 8 tight reservoir. Spontaneous imbibition experiments were conducted in oil-saturated cores, and secondary imbibition experiments were carried out in water-bearing cores. Additionally, core flooding experiments were performed to study the EOR performance of both nanoemulsion and complex surfactant. Finally, the EOR mechanisms were thoroughly investigated, specifically focusing on oil-washing capacity, reduced interfacial tension, and wettability alteration. The designed nanoemulsion, with droplets averaging 10.5 ± 0.7 nm in synthetic formation brine at ambient temperature, exhibits excellent thermal and long-term stability even under reservoir temperature conditions. The oil recovery efficiency of the nanoemulsion system in oil-saturated cores through spontaneous imbibition was 31.28%, representing a 6.42% improvement over the complex surfactant solution. In the secondary imbibition experiments, the nanoemulsion mobilized 8.53% of the residual oil, compared to 4.11% for the complex surfactant. Core flooding experiments revealed that the nanoemulsion system achieved a total oil recovery of 62.69%, outperforming the complex surfactant system by 8.68% during the chemical flooding stage and 1.82% during the subsequent brine flooding stage. The EOR mechanisms of nanoemulsion in tight reservoirs can be attributed to four aspects: reduction of oil/water interfacial tension, wettability alteration, miscibility with crude oil, and increased sweep volume. The generation of the Marangoni effect and the adsorption and diffusion characteristics are essential differences between the nanoemulsion system and the complex surfactant system. The presented findings in this paper could aid in promoting the large-scale use of nanoemulsions in Chang 8 tight reservoirs.

Formulation and characterization of ionic liquid-based nanoemulsion for enhanced oil recovery applications

Ionic liquids (ILs) are gaining attention in enhanced oil recovery (EOR) due to their potential as emulsifiers for stable oil-in-water nanoemulsions. The unique properties and stability make them promising class of chemicals, but there is a notable lack of comprehensive studies on ILs based nanoemulsions for oil recovery. In present work two methods of emulsification viz. high energy and low energy method were utilized for nanoemulsion formulation. The properties of nanoemulsions were evaluated by droplet size, zeta potential, and stability analysis. The optimized nanoemulsion formulation was further studied for EOR by assessing its miscibility with crude oil, interfacial tension reduction, wettability change, and rheological properties. The prepared nanoemulsions exhibited droplet size in a nanoscale range which decreased with emulsifier concentration. The formulated nanoemulsion formulations revealed a significant higher value (>40 mV) of zetapotential of all the IL solutions indicates higher stability of the formulated nanoemulsions. The stability was further confirmed by multiple light scattering using Turbiscan stability analyser. The excellent miscibility of the optimized nanoemulsion with crude oil holds promise for enhanced oil recovery and industrial applications. A significant lower value interfacial tension (2 mN/m at 70 °C) was obtained at optimum formulation. The nanoemulsion also showed good wettability and altered the wettability of the rock from oil-wet to water-wet. The rheological studies of nanoemulsions showed good viscous behaviour which is desirable for improved sweep efficiency. A higher viscosity of nanoemulsion (5 cp at 30 °C and 3 cp at 30 °C) compared to water improves the macroscopic sweep efficiency. The findings of this study clearly demonstrate the ability to create extremely stable crude O/W nanoemulsion, which is desirable in enhanced oil recovery.

Citrus-Based Biopolymer for Enhanced Oil Recovery Applications in High-Salinity, High-Temperature Reservoirs

Citrus-Based Biopolymer for Enhanced Oil Recovery Applications in High-Salinity, High-Temperature Reservoirs

Evaluation of Interfacial Structure of Self-Assembled Nanoparticle Layers: Use of Standard Deviation between Calculated and Experimental Drop Profiles as a Novel Method.

The self-assembly of nanoparticles (NPs) at interfaces is currently a topic of increasing interest due to numerous applications in food technology, pharmaceuticals, cosmetology, and oil recovery. It is possible to create tunable interfacial structures with desired characteristics using tailored nanoparticles that can be precisely controlled with respect to shape, size, and surface chemistry. To address these functionalities, it is essential to develop techniques to study the properties of the underlying structure. In this work, we propose an experimental approach utilizing the standard deviation of drop profiles calculated by the Laplace equation from experimental drop profiles (STD), as an alternative to the Langmuir trough or precise microscopic methods, to detect the initiation of closely packed conditions and the collapse of the adsorbed layers of CTAB-nanosilica complexes. The experiments consist of dynamic surface/interfacial tension measurements using drop profile analysis tensiometry (PAT) and large-amplitude drop surface area compression/expansion cycles. The results demonstrate significant changes in STD values at the onset of the closely packed state of nanoparticle-surfactant complexes and the monolayer collapse. The STD trend was explained in detail and shown to be a powerful tool for analyzing the adsorption and interfacial structuring of nanoparticles. Different collapse mechanisms were reported for NP monolayers at the liquid/liquid and air/liquid interfaces. We show that the interfacial tension (IFT) is solely dependent on the extent of interfacial coverage by nanoparticles, while the surfactants regulate only the hydrophobicity of the self-assembled complexes. Also, the irreversible adsorption of nanoparticles and the increasing number of adsorbed complexes after the collapse were observed by performing consecutive drop surface compression/expansion cycles. In addition to a qualitative characterization of adsorption layers, the potential of a quantitative calculation of the parameter STD such as the number of adsorbed nanoparticles at the interface and the distance between them at different states of the interfacial layer was discussed.

Experimental Investigation of the Viscosity and Stability of Scleroglucan-Based Nanofluids for Enhanced Oil Recovery.

Biopolymers emerge as promising candidates for enhanced oil recovery (EOR) applications due to their molecular structures, which exhibit better stability than polyacrylamides under harsh conditions. Nonetheless, biopolymers are susceptible to oxidation and biological degradation. Biopolymers reinforced with nanoparticles could be a potential solution to the issue. The nanofluids' stability and performance depend on the nanoparticles' properties and the preparation method. The primary objective of this study was to evaluate the effect of the preparation method and the nanoparticle type (SiO2, Al2O3, and TiO2) on the viscosity and stability of the scleroglucan (SG). The thickening effect of the SG solution was improved by adding all NPs due to the formation of three-dimensional structures between the NPs and the SG chains. The stability test showed that the SG + Al2O3 and SG + TiO2 nanofluids are highly unstable, but the SG + SiO2 nanofluids are highly stable (regardless of the preparation method). According to the ANOVA results, the preparation method and standing time influence the nanofluid viscosity with a statistical significance of 95%. On the contrary, the heating temperature and NP type are insignificant. Finally, the nanofluid with the best performance was 1000 ppm of SG + 100 ppm of SiO2_120 NPs prepared by method II.

New Trends in Biosurfactants: From Renewable Origin to Green Enhanced Oil Recovery Applications.

Enhanced oil recovery (EOR) processes are technologies used in the oil and gas industry to maximize the extraction of residual oil from reservoirs after primary and secondary recovery methods have been carried out. The injection into the reservoir of surface-active substances capable of reducing the surface tension between oil and the rock surface should favor its extraction with significant economic repercussions. However, the most commonly used surfactants in EOR are derived from petroleum, and their use can have negative environmental impacts, such as toxicity and persistence in the environment. Biosurfactants on the other hand, are derived from renewable resources and are biodegradable, making them potentially more sustainable and environmentally friendly. The present review intends to offer an updated overview of the most significant results available in scientific literature on the potential application of biosurfactants in the context of EOR processes. Aspects such as production strategies, techniques for characterizing the mechanisms of action and the pros and cons of the application of biosurfactants as a principal method for EOR will be illustrated and discussed in detail. Optimized concepts such as the HLD in biosurfactant choice and design for EOR are also discussed. The scientific findings that are illustrated and reviewed in this paper show why general emphasis needs to be placed on the development and adoption of biosurfactants in EOR as a substantial contribution to a more sustainable and environmentally friendly oil and gas industry.

Advanced polymer‐based surfactant for improved heat and salinity stability in enhanced oil recovery processes

AbstractEnhancing oil recovery through surfactants has proven to be a successful strategy in recent times. However, traditional surfactants have their limitations, particularly in terms of stability under high temperatures and salinity levels. This study delved into a groundbreaking macromolecular polymeric surfactant, S‐AV, which holds the unique ability to transform rock surface characteristics, effectively stripping away residual oil while maintaining resilience against elevated temperatures and salinity. S‐AV was synthesized through a free‐radical copolymerization process, incorporating benzyl, perfluoroalkyl, alkyl‐, benzyl‐, ethylene glycol, and amide‐alkyl‐sulfonate groups, ultimately yielding a comb‐like molecular structure. S‐AV demonstrated exceptional prowess, swiftly reducing the underwater oil contact angle to 53.4° in just 48 h. This synthesized surfactant also retained its phase stability up to salinity levels of 36,000 ppm, with temperature having no disruptive impact on its phase stability performance. Furthermore, S‐AV showcased remarkable viscosity reduction in conditions of high temperature and salinity. The core flooding experiments underscored the potential of S‐AV, as its injection led to a significant oil recovery rate of up to 83%. These findings position S‐AV as a promising candidate for practical enhanced oil recovery applications.

Preparation and evaluation of hydroxyethyl cellulose–based functional polymer for highly efficient utilization of heavy oil under the harsh reservoir environments

Emulsification viscosity reduction and subsequent demulsification are effective strategies to improve the utilization rate of heavy oil. However, traditional surfactants are challenged by unsatisfactory salt tolerance, inadequate stability in emulsification, difficulty in demulsification and pollution problem of oily wastewater discharge. To realize the feasibility and environment-friendliness of heavy oil utilization in the harsh reservoir environments, we designed a functional polymer and conducted a comprehensive evaluation using heavy oil samples from Chenping oil well in Shengli Oilfield. It was synthesized by grafting two hydrophobic monomers, lauryl methacrylate (LMA) and N, N–Diethylaminomethyl methacrylate (DEAEMA), onto the hydrophilia hydroxyethyl cellulose (HEC) by free–radical polymerization. The viscosity reduction rate can reach 99.57 % even under the high salinity of 26,050 mg/L. The stable oil–in–water (O/W) emulsion can be maintained for >48 h, satisfying the actual requirements for heavy oil recovery. Moreover, the emulsion can be completely demulsified in a CO2 atmosphere within 30 min, suggesting its satisfactory demulsification performance. Our study achieved the one–step transformation of heavy oil emulsion between emulsification and demulsification, which provides a green bio–based material and an ingenious strategy for enhanced oil recovery and other chemical engineering applications including oil/water separation.

Experimental investigation of new derived anionic natural surfactant from peanut oil: Application for enhanced oil recovery

Nowadays, there is a growing inclination towards the environmentally friendly and economically viable materials in the field of chemical enhanced oil recovery including the surfactant flooding. This study investigates the performance of a newly developed anionic surfactant derived from peanut oil in enhanced oil recovery (EOR) applications. The validity of the formulated surfactant using the esterification and sulfonation methods was verified through FTIR, 1H NMR, and TGA analytical techniques. According to the outputs of conductivity and surface tension from developed surfactant solutions at 500 and 4000 ppm, the concentration of 2000 ppm was identified as the critical micelle concentration (CMC). Several experimental tests were applied on the surfactant solutions and more specifically at CMC range, such as IFT measurement, wettability estimation, foamability, oil displacement and emulsification. The surfactant solution at CMC (optimal surfactant solution) reduced the IFT from an initial value of 15.5 to 6.8 × 10−2 mN/m at the optimum concentration of formation water (15,000 ppm). Wettability alteration was examined on sandstone and carbonate rock samples, and the optimal surfactant solution successfully altered both rock surfaces from strongly oil-wet to water-wet, resulting in a decrease in contact angle from 144° to 58° on carbonate rock and from 138° to 44° on sandstone rock. In addition, the emulsion test results revealed a significant ability of the peanut surfactant to create emulsions. Examination of microscopic images demonstrated that the emulsion remained stable for approximately 90 days with a high compatibility under high saline conditions. Hence, the developed natural surfactant enabled to displace extra 19.3 % and 15.64 % original oil in place (OOIP) from the sandstone and carbonate core plugs, respectively, with shifting the relative permeability curves towards the lift side.

Stability Evaluation of Nanofluids Suitable for Enhanced Oil Recovery

The evaluation of metal oxides nanoparticles stability in the base fluids has become a major aspect in enhanced oil recovery process in recent years. Physical and chemical properties of ZnO nanofluids have caught attention of many researchers because they are easily dispersed in the base fluids, better convective coefficient of heat transfer, and wider bandgap which make them remarkable nanofluids candidate compared to other metal oxides. In this study, the stability of nanofluid of zinc oxide nanoparticles was evaluated using different stability tests and analysis. However, ZnO nanoparticles were synthesized using sol-gel method and nanofluids of different concentrations were prepared. The prepared nanoparticles were characterized using various characterization techniques such as XRD, FTIR, TEM, and Zeta sizer. The stability of prepared nanofluids was investigated using sedimentation test, UV-vis spectrophotometer, and zeta analyzer. Based on physical investigation and UV-vis spectra observations, ZnO nanoparticles in base fluids have shown a good colloidal stability in addition to their high zeta potential values of-43.7 (mV) after seven days which makes it a successful potential candidate for enhanced oil recovery applications.

Effects of viscosity ratio and surface wettability on viscous fingering instability in rectangular channel

This paper explores the impact of viscosity ratio and surface wettability on immiscible viscous fingering instability within a rectangular channel. Numerical investigations are conducted across a range of viscosity ratios (VR) from 0.0009 to 0.5 and wall wettability ([Formula: see text]) from 15° to 150°. The volume of fluid (VOF) model is employed to track the development of finger-shaped instability at the fluid interface. Our results indicate that higher viscosity ratios lead to increased displacement efficiency. Additionally, we find the formation of necking at low VR, which diminishes at higher VR values. The finger-shaped pattern splits into two parts at a wettability of 15°; beyond this threshold, no such splitting occurs. Furthermore, a transition from hydrophilic to superhydrophobic wettability abolishes necking, resulting in enhanced displacement efficiency. Notably, as wettability shifts from hydrophilic to super hydrophobic, instability shifts toward the left side. These findings hold relevance for applications in drug delivery, clinical processes and oil recovery.

Sodium citrate-sodium hydroxide synergy on remediating asphaltene-contaminated solids

Asphaltenes are the heaviest and surface-active polyaromatic compounds in crude oil. Their precipitation and deposition on sand surfaces switch the wettability of sand from water-wet to oil-wet, which is harmful to the oil recovery process. In this study, we demonstrate the synergistic effect between sodium hydroxide (NaOH) and sodium citrate (Na3Cit) on remediating asphaltene-contaminated silica from both experimental and molecular dynamics (MD) simulation perspectives. Asphaltene desorption efficiency increased from 39 % (Na3Cit only) to 84 % (NaOH + Na3Cit), attributed to better remediation of natural silica wettability and reduced silica-asphaltene adhesion with the co-addition chemicals. Fundamental insights for NaOH-Na3Cit synergy were revealed by MD simulation. The bonding between an asphaltene model compound (C5Pe) and the quartz (101) surface became thermodynamically less favorable when both NaOH and Na3Cit were present in the system, forcing the C5Pe molecules to move away from the surface. In summary, we highlight the NaOH-Na3Cit synergy in promoting the asphaltene detachment from silica surfaces, which has important implications in oil recovery and soil remediation applications.

Constructing a viscoelastic film for enhanced oil recovery via self-adsorption of amphiphilic nanosheets at oil-water interface

Immiscible liquid-liquid interfaces have widespread applications in drug delivery, oil-water separation, oil recovery, emulsion and foam stability, etc. Here, a dense viscoelastic interface film is constructed via the self-adsorption of amphiphilic molybdenum disulfide nanosheets at the oil-water interface, which has significant implications for enhanced oil recovery. The microscopic dispersion characteristics of amphiphilic nanosheets in water phase are characterized using Cryo-EM, and the adsorption regularities of amphiphilic nanosheets in horizontal and vertical directions of oil-water interface are also revealed. Besides the mechanical response and rheological properties of interface adsorption film are systematically studied. Experimental results demonstrate that the amphiphilic nanosheet can self-curl to form a single amphiphilic nanosheet with a size of 30 nm in the water phase as the amphiphilic nanosheets concentration is lower than 50 mg/L. When the amphiphilic nanosheets concentration reaches 100 mg/L, obvious water-phase aggregation behaviors happen. The amphiphilic nanosheets can reduce the oil-water interfacial tension from 18.47 mN/m to 0.27 mN/m by forming multilayer adsorption at the oil-water interface. The adsorption ratio of amphiphilic nanosheets from bulk phase to oil-water interface can reach 97.50 %. In addition, the oil-water interface adsorption film exhibits excellent elastic properties and higher strength because the amphiphilic nanosheets can form a planar network structure at the oil-water interface which can be also directly observed in microfluidic pores. The storage modulus and interface shear viscosity of interface adsorption film are 1.65 Pa and 1.38 mN·s/m, respectively. In theory, the required desorption energy of a single amphiphilic nanosheet from oil-water interface to bulk phase is deduced to be 587 KBT. This work is expected to provide amphiphilic molybdenum disulfide nanosheet as an effective candidate for enhanced oil recovery.

Nonionic Surfactant Blends for Enhanced Oil Recovery in High-Temperature Eagle Ford Reservoir

Summary Nonionic surfactants have proven successful and cost-effective in enhancing production from conventional and unconventional reservoirs. However, studies into the mechanism and performance of nonionic surfactants have been limited to reservoirs with temperatures below 200°F due to the temperature-dependent physiochemical properties, especially cloudpoint (CP). In this study, nonionic-ionic surfactant blends were designed to create nonionic systems with cloudpoint temperatures (CPTs) above 300°F for wettability alteration in high-temperature reservoirs like the Eagle Ford Shale in Texas, USA. Through CP, wettability, interfacial tension (IFT), and spontaneous imbibition experiments, 22 commercial surfactant samples (individual and blends) were investigated. Results showed that the amount of ionic cosurfactant affected thermal stability, with increasing concentration leading to increasing CPT. Wettability alteration was dependent not only on temperature but also on the class of ionic cosurfactant. Cationic cosurfactants were superior at improving nonionic surfactants’ thermal stability. However, they resulted in oil-wet contact angles (CAs) with increasing temperature. On the other hand, anionic cosurfactants displayed better synergy in terms of wettability alteration, creating strongly water-wet and intermediate-wet CAs at high temperatures. Therefore, the focus was placed on nonionic-anionic surfactant blends for the reservoir samples used in this study. Stable surfactant blends with CPTs from 316°F to 348°F were successfully created for enhanced oil recovery (EOR) applications at high-temperature conditions. Spontaneous imbibition studies using these blends indicated improved recovery by up to 173%. This work validates and builds upon previous studies of surfactant performance, wettability alteration, and IFT while providing new insight into nonionic surfactant blends at temperature conditions not currently available in the literature. It also serves as a template for the surfactant screening and selection process when considering nonionic surfactants.

Horizontal and Vertical Comparison of Microbial Community Structures in a Low Permeability Reservoir at the Local Scale.

Petroleum microorganisms play a crucial role in the application of microbial-enhanced oil recovery, and the community structures of petroleum microorganisms have been widely studied. Due to variations in reservoir geological conditions, reservoir microbial communities exhibit unique characteristics. However, previous studies have primarily focused on microbial community changes within a single well, a single block, and before and after water flooding, and thus, cross-horizon and cross-regional comparative studies of in situ microbial communities are lacking. In this study, the 16S rRNA full-length sequencing method was adopted to study bacterial communities in crude oil samples taken from two wells at the same depths (depths of 2425 m and 2412 m) but approximately 20 km apart in the Hujianshan oilfield, located in the Ordos Basin. At the same time, the results were combined with another layer of research data from another article (from a depth of 2140 m). The aim was to compare the differences in the microbial community structures between the oil wells on a horizontal scale and a vertical scale. The results revealed that there were minimal differences in the microbial community structures that were influenced by the horizontal distances within a small range (<20 km), while differences were observed at a larger spatial scale. However, the dominant bacteria (Proteobacteria and Bacteroidetes) in the different oilfields were similar. Vertical depth variations (>300 m) had significant impacts on the communities, and this was mainly controlled by temperature. The greater the depth, the higher formation temperature, leading to an increase in thermophilic and anaerobic bacteria within a community.