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The success of foam-induced flow diversion in fractured carbonates hinges on proper injection strategies, requiring an in-depth understanding of the factors responsible for stimulating fracture–matrix interactions. In this study, we present a novel investigation of the interactions between the fracture and the matrix influenced by the mobility control effect during CH4-foam injections. These interactions were probed at the pore scale using a three-phase flow system integrated with a high-resolution micro-CT scanner. In situ phase saturations were monitored and quantified to interpret the resulting fluid transport at various injection parameters. At the initial stage of foam injection, the surfactant solution was able to invade the matrix leading to water/oil displacement events, however, impeding gas penetration. Increasing total injection velocity produced higher in situ foam quality in the fracture than the injected quality, where significant fraction of the surfactant solution from the foam was primarily diverted into the matrix. A pronounced increase in the average gas saturation within the matrix was only observed at the highest injection velocity. The pore-scale evidence showed the occurrence of combined displacement processes (water/oil, gas/oil, gas/oil/water) in the matrix, attributed to the established mobility control in the fracture, which contributed to the diversion of surfactant solution and gas to the matrix. Lastly, the injection–soaking–production technique effectively mobilized the residual oil after a long injection process of CH4-foam. At this stage, the surfactant solution was no longer playing a role as the primary invading fluid; rather, it was the diverted gas that led to the increase in the matrix-oil production. [ABSTRACT FROM AUTHOR]

Foam-based enhanced oil recovery methods are becoming instrumental in increasing hydrocarbon production from unconventional reservoirs. However, the efficacy of such techniques is significantly affected by reservoir heterogeneity and adverse wettability conditions. This experimental study addresses such challenges by investigating the effect of fracture-matrix permeability contrast on the effectiveness of foam-based enhanced oil recovery in fractured oil-wet porous systems under reservoir conditions. Fractured oilwet Minnesota Northern Cream Buff carbonate core samples were employed and fracture permeability was varied using four different mixtures of proppants with varying mesh sizes. An amphoteric surfactant was used as the foaming agent and the aqueous solution was prepared in a synthetic brine of 200,000 ppm salinity. The results showed that foam reduced gas mobility in fractures, diverting gas to the matrix and mobilizing oil toward fractures. The permeability of the fracture showed a significant impact on foam behavior in oil-wet porous systems. It was noted that as the fracture-matrix permeability contrast decreased to a certain ratio, the apparent viscosity of the foam increased, resulting in the enhancement of fracture-matrix interactions and, therefore, higher oil recovery. However, further reduction in this ratio resulted in a significant decline in foam strength. The optimal fracture-matrix permeability contrast was determined when using 100 wt.% of 100 mesh sand, enabling the creation of small and durable bubbles, which notably restricted gas movement and led to higher oil recovery. The results confirm that foam can be a viable and effective alternative to traditional gas injection methods in fractured carbonates with oil-wet characteristics. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) injection for enhanced oil recovery (EOR) has attracted great attention due to its potential to increase ultimate recovery from mature oil reservoirs. Despite the reported efficiency of CO2 in enhancing oil recovery, the high mobility of CO2 in porous media is one of the major issues faced during CO2 EOR projects. Foam injection is a proven approach to overcome CO2 mobility problems such as early gas breakthrough and low sweep efficiency. In this experimental study, we investigated the foam performance of a commercial anionic surfactant, alpha olefin sulfonate (AOS), in carbonate core samples for gas mobility control and oil recovery. Bulk foam screening tests demonstrated that varying surfactant concentrations above a threshold value had an insignificant effect on foam volume and half-life. Moreover, foam stability and capacity decreased with increasing temperature, while variations in salinity over the tested range had a negligible influence on foam properties. The pressure drop across a brine-saturated core sample increased with an increasing concentration of surfactant in the injected brine during foam flooding experiments. Co-injection of CO2 and AOS solution at an optimum concentration and gas fractional flow enhanced oil recovery by 6–10% of the original oil in place (OOIP). [ABSTRACT FROM AUTHOR]

In addressing the issue of poor control over gas permeability during the CO2 flooding process in ultra-low permeability reservoirs, this study proposes the use of a low interfacial tension viscosity-increasing system as a substitute for water in CO2–water alternating flooding to enhance CO2 mobility control and increase oil recovery. The performance of the system was evaluated through tests of viscosity, interfacial tension, wettability, and emulsification properties, and the injection behavior and gas channeling prevention effect of the viscosity-increasing system with CO2 alternate flooding were investigated. The results indicate that the low interfacial tension viscosity-increasing fluid exhibits good thickening properties, interfacial activity, hydrophilic wettability, and oil–water emulsification performance, also demonstrating strong environmental adaptability. The CO2–low interfacial tension viscosity-increasing fluid alternate flooding shows good injectivity in ultra-low permeability cores (1.085 mD). Following water flooding in heterogeneous ultra-low permeability cores, the implementation of CO2 low interfacial tension viscosity-increasing fluid alternate flooding can lead to a 15.91% increase in overall recovery compared to water flooding, outperforming CO2 flooding and CO2–water alternating flooding. The mechanisms by which the CO2 low interfacial tension viscosity-increasing fluid enhances oil recovery include reducing interfacial tension, improving mobility ratio, altering rock surface wettability, and emulsification effects. The low interfacial tension viscosity-increasing systems demonstrate effective mobility control and oil displacement capabilities and synergistically enhance the efficiency of CO2, presenting potential application prospects in the development of CO2 flooding in ultra-low permeability reservoirs. [ABSTRACT FROM AUTHOR]

Optimal core length for enhanced oil recovery (EOR) core flood experiments lacks consensus. Shorter cores are commonly used, but assessing sweep efficiency in mobility control EOR methods, crucial for longer inter-well distances, remains a question. The adequacy of shorter cores in evaluating sweep efficiency in these EOR processes needs attention. Despite the recognized importance of core flood for enhanced oil recovery (EOR) applications, there is no consensus in the literature on the optimal core length to be used in displacement experiments. Therefore, it is important to address the key question "whether the shorter length cores are sufficient for proper sweep efficiency evaluation in mobility control-based EOR processes?". The objective of this study is to investigate the effect of core length on the core-scale sweep efficiency and ultimate recovery for the displacement experiments carried out at different viscosity ratios between injected fluid and residing oil. Two identical core flooding experiments were conducted using cores that have similar porous media properties ensured through chromatography scan (CT) but have different lengths of 3 and 7 inches. Two different viscosity ratio conditions (10, 0.1) were imposed sequentially in each of the core flooding experiments by injecting water at 2 ft/day as a primary slug and then 2,000 ppm HPAM polymer solutions at 0.25 ft/day as the secondary slug. The results suggest that the use of shorter-length cores for displacement experiments under unfavourable viscosity ratio conditions would overestimate the early sweep effect by over 10%. In contrast, polymer flood conducted under favourable viscosity ratio conditions resulted in a higher-pressure gradient of 95 psi and showed only a marginal ∼ 2% difference in the incremental recovery factor between shorter and longer cores from ∼ 0.4 PV to 1.9 PV injections. [ABSTRACT FROM AUTHOR]

In response to the contradiction between the deep mobility control capability and near-well-bore area injectability of oil displacement agents， this paper proposed that an ideal oil displacement agent for mobility control should fulfill the technical requirements of low viscosity preparation/transportation， low adsorption in the near-well-bore area for long-term stable injection， and produced liquid with low concentrations of the component. Meanwhile， multi-level flow resistance peaks （Δpmax） at different positions in the deep reservoir should be established during the flow process， and flow resistance of fluid after displacing front should be maintained at a lower level. Based on the synergistic effect of the adsorption at the solid/liquid interface and the inter-molecular interaction， a hydrophobically associating water-soluble polymer/anionic surfactant binary system was designed with the characteristics of dynamically changing the system constituent and microscopic solution structure， thereby changing flow resistance. Compared with HP-1 （1 500 mg/L）， the binary systems HP-1 （1 500 mg/L）/SDSB （150 mg/L） and HP-1 （1 500 mg/L）/SDSB （200 mg/L）， with similar apparent viscosity and different constituents can construct dynamic flow resistance with higher values and better spatial distribution in the middle-rear position of the porous medium flow during the slug injection and subsequent water flooding processes. It verified that the binary system had the characteristics of viscosity increasing and delayed breakthrough during migration， and the mobility control capability in the displacing front was more powerful. In addition， the spatial distribution of flow resistance in the reservoir becomes more reasonable， which prolonged the overall breakthrough time of the slugs， thus expanding the swept volume and enhancing the oil displacement efficiency. Oil displacement experiments were conducted in a Bohai Oilfield with heavy oil， strong heterogeneity， and 80% water cut during water flooding， with chemical industrial products with basically the same dosage and similar cost adopted. The results show that the spatial dynamic distribution characteristics of the binary system before subsequent water flooding breakthrough are a crucial factor affecting oil displacement efficiency， and the binary system （AP-P4 （1 400 mg/L） + ZX-27（300 mg/L）， viscosity of 6.4 mPa·s） can improve the oil recovery by more than 10% compared with hydrophobically associating water-soluble polymer AP-P4 （1 750 mg/L， viscosity of 62.9 mPa·s）.

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The Niger-Delta basin have produced for more than 50years using the natural or primary recovery system, and has transitioned into secondary recovery after which the enhanced oil recovery (EOR) is utilized. The primary and secondary recovery systems are barely able to produce 30-35% of the oil initially in place leaving 65-70% residual oil in the reservoir. With the increase in energy demand, difficulty in detection of potential hydrocarbon reservoir and increase in drilling cost, there is need to optimally recover residual oil accumulated in the reservoir. Chemical enhanced oil recovery (CEOR) which uses alkaline, polymer, surfactant and a combination of these is utilized to recover trapped oil through a combination of mechanisms. These chemicals are expensive, imported and bedeviled with several challenges. Studies have shown the potentials of local materials to favourably match and compete with conventional chemicals in EOR. This work is a review study that focuses on local materials deployment for ASP formulation to enhance the recovery of oil. The biggest challenge for local materials is that most of them are edible. Interestingly, the use of agro-wastes from plants with similar features as the edible local materials has been suggested for ASP formulation and these edible local materials shall be cultivated in large quantities to meet global consumption and industrial utilization thereby providing jobs and also creating wealth. Some of these local agro-materials are stable in saline environment and at elevated temperatures in comparison with the conventional chemicals. The utilization of local ASP materials will reduce oil production cost; improve Nigerian economy as their cost will be independent on the global oil price, transform waste to wealth and above all job opportunities creation for Nigerians. From the review, studies show that several local materials and process mechanisms were considered for CEOR. Results from these studies showed the potentials of local materials in replacing conventional materials in EOR with local surfactant such as carica papaya extract and detergent yielding 94.1% and 96.6% displacement efficiency; local alkali - Akanwu and palm bunch ash yielded 99.1% and 97.5% displacement efficiency while local polymer - Okro and Terminalia mantaly (TM) yielded 99.1% and 90% displacement efficiency respectively. The hybridization of the local materials in AP, AS, SP and ASP gave a displacement efficiency above 70%. From the study, the aforementioned local materials have evidently proven to be effective substitute to conventional CEOR materials while materials like require further modification and processing to adequately match the conventional agents. [ABSTRACT FROM AUTHOR]

CO2 foam injection has been shown to be effective under reservoir conditions for enhanced oil recovery. However, its application requires a certain stability and surfactant absorbability on rock surface, and it is also associated with borehole corrosion in the presence of water. Adding surfactants to CO2 can enhance the interaction between CO2 and crude oil and control the CO2 mobility, thereby improving the performance of CO2 flooding. This paper presents a review of the research of CO2-soluble surfactants and their applications. Molecular dynamics simulation is introduced as a tool for analyzing the behavior of the surfactants in supercritical CO2 (scCO2). The applications of CO2-soluble surfactants, including CO2 thickening, reducing miscibility pressure, and generating supercritical CO2 foam, are discussed in detail. Moreover, some opportunities for the research and development of CO2-soluble surfactants are proposed. [ABSTRACT FROM AUTHOR]

Diutan gum (DG) is an anionic polysaccharide produced by Sphingomonas sp. ATCC 53159. The DG‐enhanced foam (DGEF) formed by the DG and foam has great application potential in enhanced oil recovery. In this research, the influence of injection parameters on DGEF was studied by conducting orthogonal experiment, with residual resistance coefficient (Rff) as the main evaluation index. The micro‐state of the foam was observed using an etching model and scanning electron microscope. The mechanism of different factors on the mobility control ability of the foam was discussed based on the apparent viscosity and surfactant depletion. The results show that the Rff of foam is correlated with the apparent viscosity, and the foam with high apparent viscosity had a good flow control ability. The calculation of the surfactant depletion shows that the bubble stability decreased significantly when the concentration of Sodium alpha‐olefin sulfonate (AOS) cannot meet the minimum stabilization concentration, thus weakening the mobility control ability. Based on the study of crude oils, the presence of oil phase will seriously weaken the mobility control ability of DGEF, but the effect of oil with higher content of resin and asphaltene will be relatively weak. [ABSTRACT FROM AUTHOR]

In colonial French Congo, one of the main challenges for labor relations was the need to reconcile contradictory efforts to promote the mobility of native workers while also stabilizing (or immobilizing) the workforce. As the interests of colonial employers and officials overlapped and merged, so did the status of indigenous workers evolve according to how administrative and economic leaders categorized indigenous work. Indigenous workers were therefore progressively categorized as migrant workers, deserters or vagrants. The political instruments which were supposed to ensure the circulation of migrant workers particularly (the laissez-passer, worker logbooks, orders regulating the flow of the workforce within the colony, etc.) were perversely used to constrain worker movement. Drawing on the archives of the French colonial administration and the private archives of the Compagnie Française du Haut-Congo, this article tries to grasp the relation between freedom and (im)mobility in the context of a colonial concession. In that context, colonial leaders sought to control of mobility for purposes relating to the construction of a local labor market, the consolidation of governmental rationality and the stabilization of colonial order. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) injection for enhanced oil recovery (EOR) has attracted great attention due to its potential to increase ultimate recovery from mature oil reservoirs. Despite the reported efficiency of CO2 in enhancing oil recovery, the high mobility of CO2 in porous media is one of the major issues faced during CO2 EOR projects. Foam injection is a proven approach to overcome CO2 mobility problems such as early gas breakthrough and low sweep efficiency. In this experimental study, we investigated the foam performance of a commercial anionic surfactant, alpha olefin sulfonate (AOS), in carbonate core samples for gas mobility control and oil recovery. Bulk foam screening tests demonstrated that varying surfactant concentrations above a threshold value had an insignificant effect on foam volume and half-life. Moreover, foam stability and capacity decreased with increasing temperature, while variations in salinity over the tested range had a negligible influence on foam properties. The pressure drop across a brine-saturated core sample increased with an increasing concentration of surfactant in the injected brine during foam flooding experiments. Co-injection of CO2 and AOS solution at an optimum concentration and gas fractional flow enhanced oil recovery by 6–10% of the original oil in place (OOIP).

Hydrophobically-modified cellulose derivatives have been considered for improved oil recovery applications. However, the subsurface reservoir environment defined by combinations of brine salinity, temperature, and porous media-induced shear can pose an adverse challenge to the mobility control prospects of these materials. Previous studies have focused mostly on amphiphilic cellulose ethers. This study is based on a cellulose ester, herein, a novel polymeric surfactant derived from sodium cellulose sulfate is investigated. Rheological studies were carried out on the novel material under variable external reservoir conditions. From the results, the amphiphilic polymer was able to initiate associative behavior at a low concentration of 0.15 g/L. The biopolymeric surfactant exhibited tolerance to temperature and shear over the tested range of 35 °C to 75 °C, and 100 RPM to 250 RPM respectively by retaining its original rheological profile. The viscosity improved over a brine salinity range of 10,000ppm to 60,000ppm as it increased from 45.75 cp to 49.1 cp. From these findings, it can be inferred that the novel cellulose derivative is a good mobility control agent, and should be considered for oilfield applications that target cheap, cost-effective, and environmental-friendly operations. [ABSTRACT FROM AUTHOR]

Low-Tension-Foam (LTF) flooding is an emerging enhanced oil recovery technique for low-permeability carbonate reservoirs. Foam capacity is closely related to the salinity environment (or, equivalently, the phase behavior of the oil/water/surfactant system). Therefore, the interactions between microemulsion and foam components are of primary importance in the LTF process. In this study, the phase behavior of an oil/water/surfactant system under equilibrium is analyzed, firstly by assuming perfect mixing. Meanwhile, the formation kinetics of microemulsion are monitored through a novel low-field NMR technique, which is able to provide quantitative assessment on the microemulsion evolution characteristics. Then, foam stability is examined in the absence and in the presence of Winsor-I and Winsor-III type microemulsions. It is revealed that foam stability depends on the oil solubilization (oil swollen micelle size). A decrease in the oil swollen micelle size and micellar structure effectiveness, in conjunction with an increasing salinity, leads to lower foam stability in the presence of a Winsor-III type microemulsion. [ABSTRACT FROM AUTHOR]

Carbon dioxide-enhanced oil recovery (CO2-EOR) has gained widespread attention in light of the declining conventional oil reserves. Moreover, CO2-EOR contributes to the reduction of the global emissions of greenhouse gases through CO2 sequestration in subsurface geologic formations. This method has been largely used in the petroleum industry for several decades especially for extracting oil from light-to-medium oil reservoirs approaching an advanced state of maturity. Traditionally, CO2 is used in a continuous flooding scheme for EOR. However, continuous CO2 flooding tends to be problematic due to unfavorable mobility, viscous fingering/channeling and early breakthrough of CO2, especially in the presence of reservoir heterogeneities. In this paper, recent developments in the methods used to overcome these problems are reviewed. These developments include CO2water-alternating-gas (WAG) injection, polymer-assisted CO2 injection, surfactant-assisted CO2 mobility control (CO2-foam injection), and nanoparticle-assisted CO2 flooding. Each method addresses, to an extent, one or more of the problems associated with conventional CO2 flooding. Furthermore, incorporating more than one method can provide better performance in terms of CO2 mobility control and oil recovery. In comparison with CO2-WAG and CO2-foam injection methods, the use of polymers and nanoparticles with CO2 flooding is relatively new. These two new methods were mostly investigated experimentally, at the laboratory level, and they still need further development prior to field implementation.

CO2 foam injection has been shown to be effective under reservoir conditions for enhanced oil recovery. However, its application requires a certain stability and surfactant absorbability on rock surface, and it is also associated with borehole corrosion in the presence of water. Adding surfactants to CO2 can enhance the interaction between CO2 and crude oil and control the CO2 mobility, thereby improving the performance of CO2 flooding. This paper presents a review of the research of CO2-soluble surfactants and their applications. Molecular dynamics simulation is introduced as a tool for analyzing the behavior of the surfactants in supercritical CO2 (scCO2). The applications of CO2-soluble surfactants, including CO2 thickening, reducing miscibility pressure, and generating supercritical CO2 foam, are discussed in detail. Moreover, some opportunities for the research and development of CO2-soluble surfactants are proposed.

The efficiency of CO2 injection for enhanced oil recovery and carbon storage is limited by severe viscosity and density differences between CO2 and reservoir fluids and reservoir heterogeneity. In-situ generation of CO2 foam can improve the mobility ratio to increase oil displacement and CO2 storage capacity in geological formations. The aim of this work was to investigate the ability of CO2 foam to increase oil production and associated CO2 storage potential, compared to other CO2 injection methods, in experiments that deploy field-scale injection strategies. Additionally, the effect of oil on CO2 foam generation and stability was investigated. Three different injection strategies were implemented in the CO2 enhanced oil recovery and associated CO2 storage experiments: pure CO2 injection, water-alternating-gas and surfactant-alternating-gas. Foam generation during surfactant-alternating-gas experiments showed reduced CO2 mobility compared to water-alternating-gas and pure CO2 injections indicated by the increase in apparent viscosity. CO2 foam increased oil recovery by 50% compared to pure CO2 injection and 25% compared to water-alternating-gas. In addition, CO2 storage capacity increased from 12% during pure CO2 injection up to 70% during surfactant-alternating-gas injections. Experiments performed at high oil saturations revealed a delay in foam generation until a critical oil saturation of 30% was reached. Oil/water emulsions in addition to CO2 foam generation contributed to CO2 mobility reduction resulting in increased CO2 storage capacity with foam. [ABSTRACT FROM AUTHOR]

Background. COVID-19 has challenged every country to issue the policy to control its population mobility. This policy paper discusses policies related to controlling population mobility from 2020 to the end of 2021 issued by the government agencies under the authority of the central government in Indonesia. All of these policies are accessed from the official website, then identified, and made into the appropriate categories. Policy and Implications. Mobility control was applied in two periods, namely PSBB (the Large-Scale Social Restrictions) and PPKM (Community Activity Restriction Implementation). This control was carried out strictly, but along with the vaccination program development, the government started to loosen the control depending on the number of cases and the progress of the vaccination program in the country. In the middle of 2021, the government continued to loosen the control by making presentation of the vaccination card mandatory instead of getting the COVID-19 test done. Recommendations Mobility control during PSBB and PPKM in Indonesia has proven successful in controlling the transmission of Covid-19. This initiative may prove to be the best practice to control contagious diseases even in the future. Conclusions This pandemic and its control measures in Indonesia show the strong role of the state in controlling the pandemic, as the health of the population is always the main concern.

Foams would play a substantial role in mobility control and are considered an efficient chemical agent to improve the oil recovery factor. Co-injection of foam and carbon dioxide (CO2) would be one of the optimum injectivity scenarios in fractured tight core samples. This paper aimed to experimentally investigate the surfactant alternating gas injection and CO2-foam injection and how to determine the optimum parameters like foam quality, flow rate, and the number of cycles. It is observed that 0.65 is the optimum foam quality for the fractured tight core samples, and by the increase of foam quality, the pressure drop has been decreased. By increasing foam quality, pressure drop increases up to a specific value (fg=0.65), and after this point, pressure drop has been decreased. Moreover, by the increase of injectivity cycles, pressure drop has increased subsequently. It is observed that five cycles are the optimum number of cycles, and after that, there is no pressure drop decrease in the system. Due to the surfactant property to control the mobility ratio, CO2 breakthrough has occurred at 1.2 PV. Its oil recovery factor at breakthrough is about 48%, and the total oil recovery factor is about 65%. CO2-foam were injected into the system, and due to the presence of a foaming agent in CO2, a CO2 breakthrough occurred at 1.8 PV. The total oil recovery factor is about 83% that indicated the efficiency of this scenario.

A comb like micro-blocked hydrophobic association polymer (CBHAP) with evident thickening property in high salinity and weak thickening property in fresh water was developed. Based on the unique property, we designed the injection strategy that polymer in fresh water with low viscosity was injected into the cores to improve injectivity and high salinity water was used to perform subsequent water flooding to improve mobility control ability. The factors influencing on the injectivity as well as mobility control ability were researched by the core flooding experiments. As a result, pressure fluctuation was found in the subsequent water flooding from 0.7 PV to 1.5 PV, showing obvious variation of viscosity in the cores. The phenomenon was believed to improve mobility control ability. In addition, the positive correlation between polymer concentration, salinity, injected volume and the fluctuation was found. The designed injection method for the polymer can be used to solve injectivity issue as well as improve mobility control ability in high salinity reservoir. [ABSTRACT FROM AUTHOR]

This article draws on qualitative data on journeys to Europe or Brazil undertaken by adults and teenagers from Sub-Saharan African countries to develop a conceptual analysis of the blurriness of the lines drawn between supposedly different types of movement via referencing the conceptual binary of forced/voluntary movement (such as asylum, trafficking, smuggling). It questions the liberal model of 'agency' that is employed not just by state actors, but also by many antislavery, anti-trafficking, child rights, and refugee rights activists, to construct boundaries between different 'types' of people on the move. Conceptual divisions between refugees and economic migrants, trafficked and smuggled persons, forced and voluntary labourers, child and adult migrants, and the idea of 'modern slavery', deflect attention from the structures that limit the choices open to people on the move. This article argues that the voluntary/forced binary encourages a tendency to falsely conflate choice with freedom and works to preserve the illusion that human freedom is a defining feature of liberal democratic societies rather than working to universally protect the freedoms of actual living human beings. [ABSTRACT FROM AUTHOR]

In A Modern Utopia (1905), H. G. Wells prophesised that emergent technologies of personal identification such as fingerprinting and central registries would enable the dismantling of national borders. Situating Wells's novel as a literary expression of a period of experimentation in European mobility control at the turn of the twentieth century, this essay argues that Wells's ideas about controlled borderlessness were indeed highly prescient, anticipating the recent rise of supranational mobility control à la the EU's Schengen cooperation. If Wells's theorisation of mobility control was ahead of its time, then so was his suspenseful narrative about undocumented aliens in utopia fearfully navigating a supranational surveillance state. In this essay I emphasise the correspondences between Wells's delineation of controlled borderlessness and modern-day supranational mobility control, whilst also highlighting discrepancies and discordant notes in Wells's bureaucratic-technocratic utopian vision. [ABSTRACT FROM AUTHOR]

• A novel surfactant-polymer (SP) combined system was successfully developed for heavy oil reservoirs. • The in-situ emulsification performance and synergistic collaboration mechanisms of SP system were systematically investigated. • The enhanced oil recovery (EOR) effect and mechanisms of SP system were identified with dual viscosity reduction and mobility controllability. Surfactant-polymer (SP) combined systems is an effective nonthermal method to enhance the heavy oil recovery, through in-situ emulsification and mobility control mechanisms. In this study, a novel SP system was developed using 0.2 wt% anionic surfactant (alkyl naphthol polyoxyethylene ether sulfonate, ANES) and 0.1 wt% polymer (partially hydrolyzed polyacrylamide, HPAM). The SP system had viscosity reduction rate of ∼ 98 %, viscosity ratio of oil to displaced water (μ o / μ d) of ∼ 3.95 and IFT of ∼ 0.29 mN/m, beneficial for decreasing the mobility ratio of water to heavy oil. Then, the applied performances including emulsion morphologies and stability, wettability alteration ability were systematically characterized. The results showed that the freshly O/W emulsions formed by SP system displayed uniform droplet size distribution, as well as high stability with tight interfacial film. In addition, the SP system exhibited excellent wettability alteration property with low contact angle of 18.3°. The synergistic collaboration mechanisms of surfactant and polymer include heavy oil–water interfacial tension reduction, in-situ emulsification, oil-viscosity reduction and water-viscosity increase. Finally, the static oil washing and dynamic sand-pack flooding experiments showed that the SP system exhibited high oil washing efficiency (62.89 %) and enhanced oil recovery efficiency (56.9 %) with improving the mobility controllability after the primary water-flooding process. This study indicated that the synergistic collaborations between surfactant and polymer had great potential to enhance the heavy oil recovery. [ABSTRACT FROM AUTHOR]

The EOR techniques are employed to recover more oil from mature reservoirs after the primary and secondary oil production stages. Polymer flooding as a chemical EOR method involves adding polymer molecules in order to increase water viscosity. Increasing water viscosity will improve the mobility ratio of injected fluid to reservoir fluid toward a more favorable value Therefore, vertical and areal sweep efficiencies are increased compared to typical water flooding. Polymer flooding will be most effective if applied in the early stages of a water flood while the mobile oil saturation is still high. Polymer is also a critical component when considering other chemical EOR technologies such as alkaline-polymer or alkaline-surfactant-polymer. The present study covers two main parts. In the first part, fundamental of polymer flooding as it related to experimental work and simulation are discussed. The challenge of polymer flooding applications in high temperature and high salinity (HTHS) environment is also discussed in this part. In the second part, the synergy of polymer with surfactant and alkaline as chemical enhancing oil recovery (CEOR) methods is discussed.

Unmanned aerial vehicles (UAVs) have attracted attentions due to their mobility and high possibility of the line of sight (LoS) channel. We can fully use these two properties by carefully optimizing the UAVs' trajectories and cooperating with some facilities. A UAV working as a mobile relay now attracts many interests due to its low cost and reliable performance. In this paper, we study a relaying system, where a UAV works as an aerial mobile relay to help some ground base stations send information to ground users periodically by using time division multiple access (TDMA). We aim to maximize the minimum average user rate through solving a non-convex and information causality constraints involved problem by jointly optimizing the UAV trajectory, nodes scheduling, and power allocation to ensure the fairness among all users. Finally, we propose an efficient iterative algorithm to solve a derived mixed-integer non-convex optimization problem to achieve this target by using block coordinate descent (BCD) and successive convex approximation (SCA) methods and prove the convergence of our algorithm. Simulations show the effectiveness of our proposed algorithm, some useful trade-offs and insights about the structure of our optimized trajectory, and the influence of two widely used trajectory initialization methods.

The carbon dioxide (CO2) injection is the promising enhanced oil recovery technique used in low permeability reservoirs. The presence of high permeability fractures along the matrix leads to poor sweep efficiency and gas channeling effect. The CO2 responsive mobility control gels could be a potential solution to mitigate the gas channeling effects. This work showcases the straightforward method to prepare a CO2 responsive gel by mixing aqueous suspension of nanocellulose and ethylenediamine. The addition of CO2 leads to protonation of amine which enhances the ionic strength of the solution. This promotes the agglomeration of nanocellulose to form gel. The rheological properties of the gel were studied and found to have interesting mechanical property. And the micromodel is used to visualize the mobility control phenomenon of the as prepared gel. The core flooding experiment proves that the synthesized gels were effective in low permeable cores. [ABSTRACT FROM AUTHOR]

This paper investigates four fortified borders: those between Hungary and Serbia, the USA and Mexico, Algeria and Morocco, and Pakistan and India. Starting from current border research, it asks how fortified borders control mobility, who is affected by fortifications, and how. Based on qualitative interviews, the paper finds that although all four borders are similarly fortified, they control mobility in different ways; while the Hungarian and the US border fences filter mobility, the two other borders instead block all forms of circulation. The paper conceptualizes these different types as filter borders and deadlock borders. It then examines their effects and analyzes not only how they are related to inequalities and power relations, but also how they can be used as resources. The filter borders reinforce the global gap in mobility rights by blocking migrants, whereas the deadlock borders also lead to increasing inequality within a country - between the capital and the border population - by cutting economic, social, and familial ties across the border line. The two border types also indicate different relations between neighboring states; filter borders are related to a clear gap in wealth and power, with one state exploiting the fortification to its advantage. By contrast, at the deadlock borders, the power balance is more ambiguous and contested. [ABSTRACT FROM AUTHOR]

Continuous CO 2 injection (CCI) into saline aquifers suffers from low sweep efficiency. While utilizing foam can effectively address this issue, a relatively potent foam design may undesirably reduce the injectivity of CO 2. In this study, the potential of CO 2 -soluble surfactants assisted carbon storage in carbonate saline aquifers was evaluated by core flooding tests and numerical simulations. It is found that foam can be generated at the displacement front during continuous CO 2 injection with 0.39 g/L surfactant (CCI + S, f g = 100 %). The CO 2 saturation can reach 60 % after 1.0 pore volume of CCI + S, approximately 50 % higher than that of CCI. The maximum pressure gradient is around 1.5 psi/ft at an injection rate of 1.0 ft/d in 162 mD Indiana Limestone for CCI + S. The effects of surfactant concentration, foam quality, and rock permeability were also investigated by core flooding. Moreover, the influence of surfactant partitioning and adsorption on CO 2 transport behavior was systematically evaluated by numerical simulation in synthetic and geological models, using modeling parameters that are realistic for field applications. The advantage of injecting surfactant with CO 2 is more evident in heterogeneous saline aquifers. Such novel injection strategy provides a promising approach for carbon sequestration in saline aquifers by controlling the mobility of CO 2 at the displacement front and simultaneously maintaining acceptable injectivity in the field. The CCI + S process may also impose less risk to the caprock. Expanding the potential CO 2 storage sites to heterogeneous saline aquifers could be a game-changer. Our understanding of foam dynamics in porous media could also be advanced. [Display omitted] • Continuous CO 2 injection with surfactant can improve the CO 2 storage efficiency. • Injectivity for continuous CO 2 injection with surfactant can be largely maintained. • An improved foam model with surfactant partitioning behavior is developed. • Carbon storage efficiency is improved in homogeneous and heterogeneous models. • Continuous CO 2 injection with surfactant is a game-changer technology for heterogeneous aquifers. [ABSTRACT FROM AUTHOR]

Although experimental studies confirmed the effectiveness of nanoparticles in enhanced oil recovery applications, no comprehensive investigation has been carried out to reveal the effect of different subsurface factors on this improvement. Proper application of nanoparticles mainly depends on their ability to travel long distances within a reservoir without agglomeration, retention, and blocking the pore throats. This study strengthens our understanding of the effect of the main subsurface factors on the nanofluid-assisted enhanced oil recovery. To this end, a transport approach utilizing the kinetic Langmuir model is developed and validated using experimental data. After that, the effects of reservoir rock type and its properties (clay content and grain size), the salinity of injected fluid, and the reservoir temperature on the transport and retention of nanoparticles in porous media concerning enhanced oil recovery methods are investigated. Since the concentration of nanoparticles in the injected fluid and on the rock surface (as deposited) control the mobility and wettability alteration, the effect of subsurface factors and salinity of injected fluid on this deposition is also analyzed. The results showed that the rock type and its properties significantly affect the transport and retention of nanoparticles in porous media. Brine salinity also has the most significant impact on the amount of nanoparticles deposited on the rock surface. The surface covered by nanoparticles increased from 10% to 82% after changing salinity from 3 wt % NaCl to the API brine. [ABSTRACT FROM AUTHOR]

This article draws on qualitative data on journeys to Europe or Brazil undertaken by adults and teenagers from Sub-Saharan African countries to develop a conceptual analysis of the blurriness of the lines drawn between supposedly different types of movement via referencing the conceptual binary of forced/voluntary movement (such as asylum, trafficking, smuggling). It questions the liberal model of ‘agency’ that is employed not just by state actors, but also by many antislavery, anti-trafficking, child rights, and refugee rights activists, to construct boundaries between different ‘types’ of people on the move. Conceptual divisions between refugees and economic migrants, trafficked and smuggled persons, forced and voluntary labourers, child and adult migrants, and the idea of ‘modern slavery’, deflect attention from the structures that limit the choices open to people on the move. This article argues that the voluntary/forced binary encourages a tendency to falsely conflate choice with freedom and works to preserve the illusion that human freedom is a defining feature of liberal democratic societies rather than working to universally protect the freedoms of actual living human beings.

This article is concerned with the digitisation of border security and migration management. Illustrated through an encounter between a migrant and the Visa Information System (VIS) – one of the largest migration-related biometric databases worldwide – the article's first part outlines three implications of digitisation. We argue that the VIS assembles a set of previously unconnected state authorities into a group of end users who enact border security and migration management through the gathering, processing and sharing of data; facilitates the practice of traceability, understood as a rationality of mobility control; and has restrictive effects on migrants' capacity to manoeuvre and resist control. Given these implications, the article's second part introduces three analytical sensitivities that help to avoid some analytical traps when studying digitisation processes. These sensitivities take their cue from insights and concepts in science and technology studies (STS), specifically material semiotics/ANT approaches. They concern, firstly, the ways that data-based security practices perform the identities of the individuals that they target; secondly, the need to consider possible practices of subversion by migrants to avoid control-biased analyses; and finally, the challenge to study the design and development of border security technologies without falling into either technological or socio-political determinism. [ABSTRACT FROM AUTHOR]

In this study, the authors address the problem of optimal routing and relative motion control in a network of robots. The path planning scheme has been designed using a fuzzy-based potential function employing optimal routing parameters. The optimal routing variables, such as routing probability and the transmission rate are obtained using a discrete optimisation problem. To deal with the disturbances and uncertainties in the physical system, an adaptive second-order sliding mode control(SMC) scheme has been proposed for the relative motion control of the networks of robots, where the disturbances are estimated using a novel disturbance observer and the controller parameters are updated online using an adaptive tuning algorithm derived based on Lyapunov theory. The robustness of the proposed path planner and the control scheme are validated through simulation as well as through real-time experimentation based on Pioneer P3-DX robots. The comparison results based on conventional SMC and adaptive SMC are also drawn.

During CO2 flooding, serious gas channeling occurs in ultra-low permeability reservoirs due to the high mobility of CO2. The chief end of this work was to research the application of responsive nanoparticles for mobility control to enhance oil recovery. Responsive nanoparticles were developed based on the modification of nano-silica (SiO2) by 3-aminopropyltrimethoxysilane (KH540) via the Eschweiler-Clark reaction. The proof of concept for responsive nanoparticles was investigated by FT-IR, 1H-NMR, TEM, DLS, CO2/N2 response, wettability, plugging performance, and core flooding experiments. The results indicated that responsive nanoparticles exhibited a good response to control nanoparticle dispersity due to electrostatic interaction. Subsequently, responsive nanoparticles showed a better plugging capacity of 93.3% to control CO2 mobility, and more than 26% of the original oil was recovered. Moreover, the proposed responsive nanoparticles could revert oil-wet surfaces to water-wet, depending on surface adsorption to remove the oil from the surface of the rocks. The results of this work indicated that responsive nanoparticles might have potential applications for improved oil recovery in ultra-low permeability reservoirs.

Abstract The purpose of the research is to propose a novel method of mobility control of condensed water by melamine during steam flooding process. Melamine is working as water permeability modifier in a non-foaming manner to control mobility of condensed water, supported by the theoretic analysis. Wettability alternatation, water residual resistance factor, and oil displacement efficiecy by melamine addition were investigated in the experiments. The contact angle was decreased by 3.6° at 200 °C indicating that the core tends to be more water wet upon addition of melamine. Water residual resistance factor, approximately representing water/oil mobility ratio, increased in response to the temperature elevation and increased pore volume during melamine injection. Water residual resistance factor reached close to 1 after subsequent hot water flood, which indicated that the reduced water permeability by melamine precipitation could be restored. The oil recovery by saturated melamine injection was increasd by 11.7% when temperature dropped from 200 to 160 °C, in comparison with pure water flooding under the same condition. The results verify the feasibility of melamine to enhance oil recovery by controlling mobility of condensed water in a steam flooding process.

We study a scenario where multiple drone-mounted base stations cruise freely over a macro hotspot to serve mobile users on the ground. The drone base stations move constantly and update their moving directions following our proposed mobility control algorithm. The constant movement of drones reduces the distance between the base stations and users, which in turn improves the probability of having a line of sight connection. We consider a practical user association scheme for the moving base stations, which enables user equipments to switch their serving base stations based only on the received signal strength. via extensive simulations, we demonstrate that the drone base stations moving according to our proposed algorithms can improve the average packet throughput by 82% and the 5th-percentile packet throughput by 430% compared to a baseline scenario, where drones hover over fixed locations. These improvements can be realized regardless of users' and base stations' density. The constant movement of the drones also helps reduce the total number of drones required to cover the macro hotspot.

The systematic understanding of the mobility control of polymer solution in porous media is conducive to the engineering application and development of polymer flooding technology. In this paper, two kinds of polymers (partially hydrolyzed polyacrylamide (HPAM) and MJ-10 (a hydrophobically associating polyacrylamide, HAPAM)) with different adsorption characteristics were used to build a solution system with different performance characteristics. And run a series of viscosity measurement, residual resistance factor (RRF) measurement and oil displacement experiments on man-made sand packs. The results show that the viscosity and residual resistance coefficient of polymer solution can enhance its fluidity control. The higher the viscosity of solution, the higher the RRF, and the higher the displacement efficiency. The solution system HM3 can make full use of the solution characteristics of the two polymers to obtain a moderate solution viscosity and residual resistance coefficient. Compared with a single solution H2 and M2, it can increase the oil recovery by 5% in the low permeability layer. The compound application of polymer solution will be a development direction of polymer flooding in the future. [ABSTRACT FROM AUTHOR]

• A mathematical model was developed to predict surfactant solutions' viscosity at operational conditions. • Surfactant solutions' viscosity was studied experimentally to determine the effects of different parameters. • Core flood tests were conducted to evaluate the effects of viscosity changes on oil recovery at operational conditions. • Some surfactants can play the role of both polymer and surface-active agents simultaneously. • TEM images approved the hypothesis of micelle's shape transition at higher surfactant and ion concentrations. Surfactants are widely used for enhanced oil recovery (EOR) purposes by reducing interfacial tension (IFT) of oil–water phases and wettability alteration. Some surfactants with viscoelastic properties can be used as mobility control agents due to enhanced viscosity resulting from the spherical-to-cylindrical shape transition of micelles. Dodecyltrimethylammonium chloride (DAC) shows viscoelastic behavior coupled with dominantly cylindrical shape of the micelle in ambient conditions. Nevertheless, using DAC as an IFT reduction and mobility control agent needs to be industrialized for actual operating conditions. In this study, DAC, as a cationic surfactant, was experimentally studied in reservoir conditions considering dominantly cylindrical micelles for the first time. Results showed that the viscosity of DAC solution is a strong function of DAC concentration, especially at high temperature and high salinity conditions, while it does not depend on pressure significantly. Transmission electron microscope (TEM) images were taken for a better understanding of DAC micellar structures. Analysis of the TEM results indicated the shape transition of the micelles from small spherical to large cylindrical at higher concentrations of DAC. IFT of DAC microemulsion was studied for wide ranges of temperature and DAC concentration, ruling out any significant effect of the temperature on the IFT trend line. A general mathematical model for predicting the viscosity of surfactant solution was developed and evaluated for real reservoir conditions by including all effective terms. Results showed a very good agreement with experimental data of DAC and Cetyltrimethyl ammonium bromide (CTAB, as per previous studies), justifying the applicability of the developed model for predicting the viscosity wherever experimental data is unavailable. Core flood tests were performed with saltwater (SW) and DAC solutions with spherical (SS) and cylindrical (SC) micelles as injecting phases for evaluation of IFT reduction and mobility control effects. Results showed an additional recovery factor of 13 % for SS and 23 % for SC in comparison with SW injection. [ABSTRACT FROM AUTHOR]

[Display omitted] • A kind of active amphiphilic polymer PMC16 was synthesized. • The viscosity and viscoelasticity of PMC16 increased through the entanglement and association between hydrophobic chains. • The hydrophilic and lipophilic groups in PMC16 can enter the water phase and oil phase, reducing the IFT between oil and water. • PMC16 solution altered the solid surface wettability to water-wet, which is beneficial for spontaneous imbibition. • PMC16 reduce viscosity of heavy oil through synergistic action of viscoelasticity, emulsification and altering wettability. Amphiphilic polymers represent significant ability in emulsifying crude oil during the displacement, enabling effective control the oil/water interface mobility and reduction of heavy oil viscosity. Herein, an amphiphilic polymer, named PMC16, was copolymerization using by hydrophobic monomer C16DMAAC, along with acrylamide and acrylic acid as comonomers. The structure of PMC16 was identified by 1H NMR, and FT-IR. The potential of PMC16 for oil recovery enhancement was evaluated through assessments of fluid viscoelasticity, reduction in oil viscosity, wettability alternation and interfacial activity between heavy oil and PMC16. The results reveal that PMC16 showed well shear resistance due to the hydrophobic association between its molecular chains. In addition, the PMC16 can effectively decrease the viscosity of the oil phase through emulsification. The viscosity reduction achieved by PMC16 for heavy oil surpasses 95% under the condition of 60 °C, oil–water ratio of 3:7 and a concentration of 3000 mg/L. Additionally, PMC16 solution induces a shift in the wettability of solid surfaces towards water-wet characteristics, with the oil droplet contact angle reducing from 125° to 54°. Such wettability transformation proves advantageous for spontaneous imbibition, especially when considering capillary force as the driving mechanism. Furthermore, the results of oil displacement performance experiments substantiated that PMC16 contributed to a 17.9% increase in the recovery rate of heavy oil. The utilization of PMC16 holds significant theoretical importance in augmenting the recovery of heavy oil. [ABSTRACT FROM AUTHOR]

In order to improve the CO2 foam stability at high temperature and salinity, hydrophilic silica nanoparticles (NPs) were added into a dilute zwitterionic surfactant solution to stabilize supercritical CO2 (SC-CO2) foam. In the present paper, the foaming capacity and stability of SC-CO2 foam were investigated as a function of NP concentration at elevated temperatures and pressures. It was observed that the drainage rate of SC-CO2 foam was initially fast and then became slower with NPs adsorption at the gas-liquid interface. The improved foam stability at high temperature was attributed to the enhanced disjoining pressure with addition of NPs. Furthermore, an obvious increase in the foam stability was noticed with the increasing salinity due to the screening of NP charges at the interface. The rheological characteristics including apparent viscosity and surface elasticity, resistance factor, and microstructures of SC-CO2 foam were also analyzed at high temperature and pressure. With addition of 0.7% NPs, SC-CO2 foam was stabilized with apparent viscosity increased up to 80 mPa·s and resistance factor up to 200. Based on the stochastic bubble population (SBP) model, the resistance factor of SC-CO2 foam was simulated by considering the foam generation rate and maximum bubble density. The microstructural characteristics of SC-CO2 foam were detected by optical microscopy. It was found that the effluent bubble size ranged between 20 and 30 μm and the coalescence rate of SC-CO2 foam became slow with the increasing NP concentration. Oscillation measurements revealed that the NPs enhanced surface elasticity between CO2 and foam agents for resisting external disturbances, thus resulting in enhanced film stability and excellent rheological properties.

An oscillating drop rheometer capable of operating under conditions of high pressure and high temperature has been built. The oscillating drop mechanism was able to support pressures as high as 1300 bar and successfully performed oscillations at constant pressure. Apparent elastic and viscous complex moduli were measured for a system of CO2 and synthetic seawater containing 100 ppm of a linear alkyl ethoxylate surfactant for different pressures and temperatures. The moduli had strong dependencies on both pressure and temperature. At temperatures of 40 and 80 °C, the apparent elastic modulus passed through a maximum for pressures between 100 and 300 bar. The harmonic distortion of the oscillations was calculated for all measurements, and it was found that drop oscillations below ca. 2.6 µL caused distortions above 10% due to a mechanical backlash of the motor.