Flooding Experiments Research Articles

Chemical enhanced oil recovery under Harsh conditions: Investigation of rock permeability and insights from NMR measurements

Injecting surfactant into a hydrocarbon reservoir stands out as a highly effective method for EOR due to its ability to reduce water/oil IFT and alter rock wettability in certain cases. However, the efficiency of this process is compromised in heterogeneous reservoirs, especially carbonates, characterized by significant permeability variations. This study presents findings from three core flooding experiments on heterogeneous carbonate core samples with different permeabilities. The experiments were conducted under representative reservoir conditions of 100 °C, pressures higher than 3000 psi, and seawater salinities and formation water of 57,745 ppm and 213,768 ppm, respectively. In each experiment, seawater was continuously injected followed by continuously injecting a 2500-ppm solution of in-house synthesized Gemini surfactant. Results revealed that the recovery factor was highest in low-permeability rocks and lowest in high-permeability rocks for both seawater and surfactant floods. Surfactant floods yielded additional recoveries of 31%, 23%, and 19% for low, medium, and high-permeability samples, respectively. Nuclear magnetic resonance (NMR) analysis on short analogous core plugs at different flooding stages confirmed these results. Effluent analysis on the produced aqueous phase indicated that dynamic retention was highest (0.467 mg/gm-rock) in the lowest permeability and lowest (0.146 mg/gm-rock) in the highest permeability rock. NMR analysis suggested that the surfactant's recovery performance and dynamic retention were influenced by the larger surface area of low-permeability rocks, facilitating increased contact with the surfactant. Utilizing NMR monitoring in this work enhances EOR insights through integrated studies and coreflooding experiments and establishes a novel framework for complex reservoir conditions.

Using X-ray computed tomography and pore-scale numerical modeling to study the role of heterogeneous rock surface wettability on hydrogen-brine two-phase flow in underground hydrogen storage

Underground hydrogen storage (UHS) is receiving increasing attention to address the challenges in hydrogen storage. A crucial aspect of UHS is understanding the transport of hydrogen in subsurface porous media. In this work, hydrogen core flooding experiments were conducted in a sandstone sample and then the pore-scale distribution of hydrogen and brine was visualized using high-resolution X-ray micro-computed tomography (micro-CT). After CT image processing, we measured the surface contact angles (CAs) on rock surfaces and found that the measured CAs followed a log-normal distribution. To investigate the influence of rock surface wettability on the transport properties in the hydrogen-brine-sandstone system, the lattice Boltzmann (LB) method was used to simulate two-phase flows with different surface CA distributions; hydrogen-brine relative permeability and capillary pressure curves through the primary drainage, imbibition, and secondary drainage processes were obtained by LB simulations. X-ray CT scanning showed that hydrogen resided in both large pores and small pores and pore throats after the primary drainage process (i.e., hydrogen displacing brine), whereas after the imbibition process (i.e., brine displacing hydrogen) hydrogen stayed primarily in large pores where the capillary pressure barriers were low. The LB two-phase flow modeling illustrated that water’s relative permeability increased whereas hydrogen’s relative permeability decreased when the core flooding moved from primary drainage to imbibition; in contrast, when the core flooding moved from imbibition to secondary drainage, water’s relative permeability decreased whereas hydrogen’s relative permeability increased. Decreasing the surface CA increased the capillary pressure and reduced the hydrogen residual rate, which indicates high hydrogen retrievability and thus is favorable for UHS practice. The change in CA’s standard deviation did not cause noticeable changes in water’s relative permeability curves, whereas it resulted in noticeable changes in hydrogen’s relative permeability curves. This work is the first study that utilizes X-ray micro-CT scanning and pore-scale multiphase flow modeling to quantitatively and comprehensively investigate hydrogen-brine two-phase flow properties under different rock surface wettability distributions. The research findings from this study will advance the understanding of hydrogen transport in an underground storage system and provide essential data for large-scale field studies in UHS.

β-Cyclodextrin modified SiO2 nanofluid for enhanced oil recovery

Recently, with the deterioration of oil storage conditions, the extraction of oil has been limited. In this experiment, β-cyclodextrin (β-CD) was grafted onto the surface of SiO2 nanoparticles. The structure and morphology of nanoparticles were analyzed by various characterization tools to effectively validate the synthesis of nanomaterials. In addition, it was experimentally demonstrated that the developed β-CD-SiO2 nanofluid has excellent stability and salt resistance. Finally, the comparative studies of the nanofluids were carried out by wettability, interfacial tension (IFT), Pickering emulsion, viscosity, and core flooding experiments. The results showed that β-CD-SiO2 nanofluid exhibited better performance: β-CD-SiO2 nanofluid changed the contact angle (CTA) of carbonate plate from 131.5º to 90.1º; the IFT was significantly reduced from about 35 mN/m to 22.5 mN/m; the emulsion droplets formed were fine and dense; the viscosity increased and viscosity not changed with shear rate; and total crude oil recovery up to 59.2%, 23.9% higher than using water drives. Overall, these results showed the great potential of β-CD-SiO2 nanofluid in ultra-low permeability reservoirs.

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.

PENGARUH POLIMER PC DENGAN ADDITIF TWEEN-80 TERHADAP KARAKTERISTIK POLIMER DAN RECOVERY FACTOR PADA MINYAK 39 °API DI BATUAN SANDSTONE

Background: The increasing demand for petroleum and the depletion of oil reserves in oil fields require the development of more efficient oil recovery techniques to enhance oil production. One method that can be employed is Enhanced Oil Recovery (EOR), where chemical injection becomes a viable approach. One chemical injection method that can be used is polymer injection. One suitable polymer for this purpose is cellulose polymer (PC). Cellulose polymer (PC) is the most abundant polymer in nature, a renewable material that is degradable, biocompatible, cost-effective, and non-toxic. Cellulose can be derived from plants and certain types of bacteria.Objective: This research aims to investigate the influence of temperature variations on cellulose polymer (PC) with Tween-80 additive on the Recovery Factor.Methodology: Laboratory experiments were conducted using the core flooding technique with a core holder, applying the slug method with various °API variations on light crude oil with an API gravity value of 39. Sandstone rock samples were used in the experiments, prepared by saturating with brine and oil.Result: The laboratory results showed a recovery percentage of 7.89% at a temperature of 60 °C and 17.86% at a temperature of 80 °C. The highest increase in oil recovery was observed at a temperature of 80 °C, with a recovery factor of 17.86%. In conclusion:, based on the conducted core flooding experiments, the best recovery factor was found in polymer injection using PC with Tween-80 additive at a temperature of 80 °C.

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.

Experimental investigation of the sequence injection effect of sea water and smart water into an offshore carbonate reservoir for enhanced oil recovery

This study explores enhanced oil recovery (EOR) strategies, with a focus on carbonate reservoirs constituting over 60% of global oil discoveries. While “smart water” injection proves effective in EOR for carbonate reservoirs, offshore application challenges arise due to impractical volumes for injection. To address this, we propose a novel continuous injection approach, systematically investigating it on a laboratory scale using the Iranian offshore reservoir, Sivand. Thirty-six contact angle tests and twelve flooding experiments are meticulously conducted, with key ions, potassium, and sulfate, playing pivotal roles. Optimal wettability alteration is observed at 4 times potassium ion concentration in 0–2 times sulfate concentrations, driven by ionic strength and charge interactions. Conversely, at 3–5 times sulfate concentrations, the optimal contact angle shifts to 2 times potassium ion concentration, suggesting a mechanism change linked to increasing sulfate ion ionicity. A significant wettability alteration, evidenced by a 132.8° decrease, occurs in seawater with a twofold concentration of potassium ions and a fivefold concentration of sulfate ions. Micromodel experiments introduce an innovative alternation of smart water and seawater injections. The first scenario, smart water followed by seawater injection, reveals negligible post-seawater injection oil recovery changes. In contrast, the second scenario yields a maximum recovery of 7.9%. The first scenario, however, boasts superior overall sweep efficacy, reaching approximately 43%. This research expands understanding of smart water and seawater injection in EOR, presenting a viable solution for optimizing offshore carbonate reservoir recovery. The insights contribute to evolving EOR methodologies, emphasizing tailored strategies for varying reservoir conditions.

THE EFFECT OF POLYMER GEL ON THE OIL AND WATER PERMEABILITY DAMAGE IN A MICROFLUIDIC DEVICE

Microfluidics, a rapidly advancing field, finds wide applications in various domains, including enhanced oil recovery. This study delineates the methodology for fabricating a microchip with channels having a width of 50 μm, designed to simulate and visualize fluid flow in porous media. The microfluidic device was constructed using NOA81, a UV-curable polymer. Upon curing, it forms a robust and transparent microchip structure suitable for precise fluid control and analysis in microfluidic applications. Flood experiments conducted on the microchip revealed that the introduction of a 0.5 wt% polymer gel into the model's channels resulted in a reduction of water permeability by a factor of 106 and 25 at the shock front and after injection pressure stabilized, respectively. In contrast, oil permeability was reduced by at least 40 times.

Experimental investigating of the effect of CO2 injection parameters on asphaltene precipitation and formation damage in live oil

AbstractWith the increasing consumption of oil in the world and increasing production of oil from oil reservoirs, the reservoir pressure starts to decrease. On the other side, the use of oil leads to an increase in carbon dioxide production in the environment and causes global warming.One of the effective methods of reducing the amount of carbon dioxide emitted into the atmosphere and increasing the reservoir's pressure is CO2‐EOR and carbon capturing and storing (CCS) which injects produced carbon dioxide from industrial sources into underground reservoirs. Carbon dioxide reduces oil viscosity and increases oil mobility producing an economical state. Moreover, with CO2‐EOR and CCS carbon dioxide can be stored in a depleted reservoir and helps reduce pollution and global warming.Besides the environmental and economic benefits due to reducing carbon dioxide emissions to the atmosphere and increasing oil production, CO2 injection causes various problems in the formation. Many experiments indicate that asphaltene precipitation and wettability alteration caused by asphaltene, dissolution/precipitation of rock, salt precipitation, and sludge formation are some of the problems that occur during CO2 injection operations in low pressure and temperature. However, few experiments evaluate asphaltene precipitation effective factors, such as pressure, injection rates, temperature, etc., in high temperatures and pressure (HPHT) near reservoir conditions. Therefore, there was a need for a comprehensive investigation of various factors and the impact of each of them on the asphaltene precipitation and formation damage in HPHT conditions, so this research was designed to help future simulation and industrial utilization.A core‐flood setup was prepared to conduct CO2 flooding experiments and formation damage studies in HPHT conditions. The main objective of this study was to evaluate the effect of different parameters including pressure, injection rate, and type of injected gas on asphaltene and its effect on formation damage caused by CO2 injection. The second goal of this study was to investigate the optimum injection in every section. The third goal was to determine the oil recovery during the process of CO2 injection in different conditions.The results showed that an injection rate of 0.1 cc/min and higher injection pressures minimized asphaltene precipitation and maximized oil recovery. Replacing CO2 with natural gas liquids (NGL) gas reduced oil production and asphaltene precipitation. Overall, the experiments demonstrated the importance of optimizing injection parameters to limit formation damage during CO2 flooding. © 2024 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

Study on the influence of SARA fraction in heavy oil on the oil recovery during water flooding by experiments and the molecular dynamics simulation

W/O emulsification in the J-7 reservoir has been regarded as the main reason for enhancing oil recovery. Therefore, in this article, the chemical structures of SARA fractions of JD-1 crude oil were obtained through characterization experiments, and the effect of the influence of SARA fractions on the W/O emulsification and the oil recovery by using emulsification experiments, interfacial experiments, emulsification experiments, and water flooding experiments. Results showed from emulsification experiments that the emulsification degree of the simulated oil containing asphaltenes was higher than other simulated oils. All emulsions of SARA fractions after emulsifying were W/O emulsions, but compared with other components, the performance of emulsions of asphaltenes was the best. The viscosity of emulsions reached 8.16–18.38 times that of simulated oil, the average size of was only 0.68 μm, and the stability was also very good. From interface tension and expansion modulus experiments, it can be seen that after adding asphaltenes, the decrease degree of interface tension and the increased degree of expansion modulus were the most. The result of molecules dynamic simulations showed that the adsorption force on the oil-water interface of asphaltenes was greater than other components. The water flooding experiments found the recovery of the simulated oil containing asphaltenes reached 43.81%, which was higher than other simulated oil, indicating that the easier W/O emulsification was formed, the recovery rate was higher.

Investigation of the Combination Mechanism of Spontaneous Imbibition and Water Flooding in Tight Oil Reservoirs Based on Nuclear Magnetic Resonance

As conventional oil reservoirs are gradually being depleted, researchers worldwide are progressively shifting their focus towards the development and comprehensive study of tight oil reservoirs. Considering that hydraulic fracturing is one of the main approaches for developing tight sandstone reservoirs, it is of great significance to explore the mechanism of spontaneous imbibition and waterflooding behavior after hydraulic fracturing in tight oil reservoirs. This research delves into the analysis of tight sandstone core samples obtained from the Shahejie Formation in the Bohai Bay Basin. All core samples are used for a series of experiments, including spontaneous imbibition and water flooding experiments. An additional well-shut period experiment is designed to understand the impact and operational dynamics of well shut-in procedures in tight reservoir development. Utilizing nuclear magnetic resonance (NMR) technology, the pore sizes of a sample are divided into three types, namely, macropores (>100 ms), mesopores (10–100 ms), and micropores (<10 ms), to thoroughly assess the fluid distribution and changes in fluid signals during the spontaneous imbibition and water flooding stages. Experimental outcomes reveal that during the spontaneous imbibition stage, oil recovery ranges from 12.23% to 18.70%, predominantly depending on capillary forces. The final oil recovery initially rises and then falls as permeability decreases, while the contribution of micropores progressively grows as the share of mesopores and macropores deceases. With water flooding processes carried out after spontaneous imbibition, enhanced oil recovery is observed between 28.26% and 33.50% and is directly proportional to permeability. The well shut-in procedures can elevate the oil recovery to as high as 47.66% by optimizing energy balance.

Enhanced oil recovery by using modified ZnO nanocomposites in sandstone oil reservoirs

Recently, nanocomposites were employed to improve the extraction of oil in different reservoirs. Due to the unique characteristics of nanoparticles such as small size, efficient altering main mechanisms such as IFT, CA, and viscosity reduction, have received wide attention among researchers. This study investigated the application of a newly designed ZnO-cerium N-composite for EOR at reservoir conditions, and the performance was compared to the standalone ZnO nanoparticles. After performing the morphology of the N-composite, the effect of the N-composites on the wettability alteration, interfacial tension, viscosity, Zeta potential, pH, and density was studied at different N-composites concentrations at reservoir conditions. Based on the results of rock/fluid interactions at the static phase, an optimum concentration was chosen for performing dynamic core flooding experiments. At 100 ppm, the highest stability and the highest reduction in capillary force were observed. The presence of Ce in the structure of the N-composite changes the pore volume of ZnO-Ce compared to ZnO nanoparticles, which affects the surface charge. IFT (mN/m), CA (°), and zeta potential (mV) were (22.51, 40.83, and − 44.36), and (30.50, 50.21, and − 31.05) for ZnO-Ce and ZnO, respectively at 100 ppm. By application of the optimized nanofluid in an oil displacement study, RF in the presence of ZnO-Ce, and ZnO were 37.11% and 71.40%, respectively.

A New Mechanistic Model for Wettability-Altering Surfactant Floods in Carbonates

Summary Surfactants and low-salinity brines have been shown to be effective for enhanced oil recovery in carbonate rocks through wettability alteration (WA). Oil wettability of carbonates is ascribed to the adsorbed organic acid components in oil. The removal of the adsorbed acids leads to WA. Previous experiments with wettability-altering surfactants have shown the following: WA is a slow process; acid removal is irreversible in most cases; surfactants can access the rock surface in water-wet regions and at three-phase contact lines rather than the entire rock surface; surfactant molecules become inactive after interactions with acids. Existing models/simulators do not incorporate the aforementioned observations. In this work, a multiphase, multicomponent, finite-difference reservoir simulator incorporating a new mechanistic model for WA was developed. The model captures the key physicochemical reactions between adsorbed acids and surfactant molecules and honors the four experimental evidences. The model was first tested at the core scale. The simulation results demonstrated that the model can accurately predict waterflood performance in rocks with various wettability. It can also effectively account for the influence of injection rates in surfactant flood experiments. The effectiveness of the surfactant, controlled by an interaction constant in the model, was found to be a dominant factor. The model was also tested for field-scale pilot tests. The results revealed that total quantity of chemicals injected and the injection rate have a more pronounced effect on oil recovery compared to the timing of surfactant treatment and the concentration of surfactant slug.

Nano-structure of hydrolyzed polyacrylamide strengthened ultra stable nitrogen foam: Lab experiments and molecular dynamics simulation

Foam flooding is an extremely effective method of enhanced oil recovery used to address uneven utilization in strongly heterogeneous reservoirs. However, conventional foam is not stable and is unevenly distributed in oil reservoirs during conventional foam flooding. Hydrolyzed polyacrylamide-strengthened nitrogen foam (HSNF) was therefore proposed to overcome the defects of conventional foam flooding. In this investigation, a comprehensive method was utilized to understand the mechanisms of HSNF with regard to its stability and distribution in reservoirs. In situ experimental characterization and molecular dynamics simulations were designed to examine the characteristics of HSNF. Foam stability was analyzed as a function of the viscosity of the liquid phase, adsorption, and pressure for HSNF and conventional foam. Parallel core flooding experiments were conducted to compare the oil recovery efficiencies of HSNF and conventional foam. Molecular dynamics simulations were utilized to examine the nanostructure of HSNF in brine. Foam stability tests demonstrated that foam stability was enhanced by increasing the viscosity and pressure of the liquid phase and reducing the adsorption capacity of the surfactant. HSNF increased the foam half-life by a factor of 1.67–27.1. The parallel core flooding experiments showed that HSNF effectively initiated flow in low-permeability cores to increase the mobilization of oil even when the permeability ratio was 14.86. However, conventional foam only achieved similar performance at a permeability ratio of less than 10.64. The molecular dynamics simulations revealed that the addition of hydrolyzed polyacrylamide improved the uniform distribution of the oil displacement agent in porous media, inhibited the diffusion of nitrogen in the foam system, and enhanced the interactions between the water phase and crude oil. This suggests that HSNF is a promising oil recovery agent for use in low-porosity, low-permeability, and strongly heterogeneous sandstone reservoirs.

The impact of heterogeneity and pore network characteristics on single and multi-phase fluid propagation in complex porous media: An X-ray computed tomography study

This study investigates the impact of pore network characteristics on fluid flow through complex and heterogeneous porous media, providing insights into the factors affecting fluid propagation in such systems. Specifically, high-resolution or micro X-ray computed tomography (CT) imaging techniques were utilized to examine outcrop stromatolite samples of the Lagoa Salgada, considered flow analogous to the Brazilian Pre-salt carbonate reservoirs. The petrophysical results comprised two distinct stromatolite depositional facies, the columnar and the fine-grained facies. By generating pore network model (PNM), the study quantified the relationship between key features of the porous system, including pore and throat radius, throat length, coordination number, shape factor, and pore volume. The study found that the less dense pore network of the columnar sample is typically characterized by larger pores and wider and longer throats but with a weaker connection of throats to pores. Both facies exhibited less variability in the radius of the pores and throats in comparison to throat length. Additionally, a series of core flooding experiments coupled with medical CT scanning was designed and conducted in the plug samples to assess flow propagation and saturation fields. The study revealed that the heterogeneity and presence of disconnected or dead-end pores significantly impacted the flow patterns and saturation. Two-phase flow patterns and oil saturation distribution reveal a preferential and heterogeneous displacement that mainly swept displaced fluid in some regions of plugs and bypassed it in others. The relation between saturation profiles, porosity profiles, and the number of fluid flow patterns for the samples was evident. Only for the columnar plug sample was the enhancement in recovery factor after shifting to lower salinity water injection (SB) observed.

Evaluation of Novel Preformed Particle Gel System for Conformance Control in Mature Oil Reservoirs.

To address challenges associated with excessive water production in mature oil reservoirs, this study introduces a carboxymethyl cellulose (CMC)-based material as a novel preformed particle gel (PPG) designed to plug excessive water pathways and redistribute the subsequent injected water toward unswept zones. Through microwave-assisted grafting copolymerization of CMC with acrylamide (AM), we successfully generated multi-sized dry particles within the range of 250-800 µm. Comprehensive analyses, including Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), have confirmed the chemical composition and morphology of the resulting carboxymethyl cellulose-grafted crosslinked polyacrylamide (CMC/PAMBA). Swelling kinetics and rheology tests were conducted to confirm the ability of this novel PPG system to perform at different reservoir conditions. The results of core flooding experiments showed that the CMC/PAMBA PPG is capable of plugging open fractures with a water breakthrough pressure gradient of up to 144 psi/ft. This preformed particle gel (PPG) system was designed specifically for application in Middle East reservoirs, which are distinguished by high salinity and elevated temperature levels. This PPG system is able to swell up to 10 times its original size in seawater and maintain a strength of about 1300 Pa at a temperature of 80 °C. Further optimization is conceivable to enhance injection efficiency and achieve superior plugging outcomes.

Dual-responsive emulsion system: Unraveling pH and host-guest interactions for emulsion stability and enhanced oil recovery

Surfactants facilitate the formation of crude oil emulsions in the petroleum reservoir and reduce oil-water interfacial tension, playing a crucial role in tertiary oil recovery. The host-guest interactions between β-cyclodextrin (β-CD) and surfactant molecules can regulate the solubility and hydrophobic interactions of surfactants, further regulating the interfacial and solution aggregation behaviors of the system. A ternary system composed of β-CD, nonionic surfactant Span 80, and anionic amino acid surfactant was designed to act as emulsion stabilizers and promote emulsion formation. Due to the pH responsiveness of the amino acid surfactant and host-guest interactions between the hydrophobic tail of the surfactant and β-CD, the emulsions exhibit dual responsiveness. The pH and β-CD host-guest interaction dual responsiveness determines the emulsion properties. By adjusting the proportion of β-CD in the ternary system and solution pH, the stability, droplet morphology, and rheological properties of the emulsions are all significantly affected. Interactions among emulsion stabilizers as well as their interfacial behaviors were analyzed using 1H NMR spectroscopy and interfacial tension analysis. This type of emulsion was also tested in core flooding experiments, clearly showing that the response of the emulsions to host-guest interactions can enhance crude oil recovery. Incorporating a higher concentration of β-CD into the system can boost additional secondary oil recovery by approximately 32%, while its pH responsiveness facilitates the demulsification of the system after the flooding. These research findings not only highlight the unique properties of the multi-responsive emulsion but also deepen our understanding of the interactions between surfactants. The ternary stabilizer system developed in this study demonstrates broad potential applications in flooding and oil-water separation.

Comprehensive Study on Microscopic Pore Structure and Displacement Mechanism of Tight Sandstone Reservoirs: A Case Study of the Chang 3 Member in the Weibei Oilfield, Ordos Basin, China

With the continuous growth in global energy demand, research and development of unconventional oil and gas reservoirs have become crucial in the field of energy. This study focuses on the Chang 3 reservoir of the Yanchang Formation in the Ordos Basin, Weibei Oilfield, China. This reservoir is a typical tight sandstone reservoir, and its microscopic pore structure and displacement mechanism are essential for the efficient development of tight oil. However, the reservoir faces challenges such as complex microscopic pore structures and unclear displacement mechanisms, which hinder the efficient development of tight oil. In light of these challenges, through various studies including core observation, high-pressure mercury injection tests, water flooding experiments, oil-water two-phase relative permeability measurements, and stress sensitivity experiments, it was found that the Chang 3 reservoir exhibits strong microscopic heterogeneity. The pore-throat distribution characteristics mainly present two types: single peak and double peak, with the double peak type being predominant. The reservoir was classified and evaluated based on these characteristics. The improved injection ratio and properties enhance oil displacement efficiency, but an increase in irreducible water saturation has a negative impact on efficiency. The stress sensitivity of the reservoir fluctuates between weak and strong, with permeability being sensitive to net confining pressure. It is recommended to pay particular attention to the stress-sensitivity characteristics during reservoir development. The research results provide a scientific basis for the optimized development of tight oil reservoirs in this region, promote the sustainable development of unconventional oil and gas resources, and have significant theoretical and practical implications.

Enhanced hydrogen sequestration through hydrogen foam generation with SDS Co-Injection in subsurface formations

Inherent obstacles of hydrogen injection encompass preferential channeling through larger pathways, hampering microscopic sweep efficiency within porous media. This work pioneers hydrogen foam generation via co-injection with aqueous sodium dodecyl sulfate (SDS) to enhance subsurface hydrogen trapping capacity. SDS addition substantially reduces hydrogen-water interfacial tension and enhances viscoelasticity. In contrast to robust hydrogen foam stability, CO2 foams display compromised integrity, stemming from surfactant aggregation and ensuing infiltration channels that permit aqueous phase CO2 dissolution. Hydrogen foams conversely sustain uniform surfactant films, forestalling hydrogen ingress into water. Synergetic microfluidic and pore-scale simulations visualise mechanisms underlying intensified hydrogen capture and mobility reduction attributed to deformation and flow resistance when traversing constricted pores. Introducing the amphiphilic SDS surfactant considerably promotes hydrogen adsorption through its hydrophobic tail. Core flooding experiments quantify over 2 times hydrogen storage ratio amplification with SDS relative to sole hydrogen injection. The framework contributes pragmatic strategies to harness high-efficiency hydrogen foam for scalable clean energy storage.

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.