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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).

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.

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.

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.

The paper focused on a portable selection which allows a robot at low cost to recognize guests before and guide them to their destinations. First, we begin with a brief description of the Greeting Robot and the methods introduction we used in our robot. After that, we focus on how to accomplish the movement control of the mobile robot platform. Specially, we discuss a lot of cases to find the better way to make the robot avoid crashing on its own. Then we also focus on the programing about how to complete the target of facial recognition and maintaining the database by itself and how to ensure the interaction between RaspberryPi and Arduino.

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.

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.

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.

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.

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.

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.

In this study, oil production and retention were observed and compared in 72 reservoir simulation cases, after which an economic analysis for various CO2 and oil prices was performed. Reservoir simulation cases comprise different combinations of water alternating gas (WAG) ratios, permeabilities, and well distances. These models were set at three different depths; thus different pressure and temperature conditions, to see the impact of miscibility on oil production and CO2 sequestration. Those reservoir conditions affect oil production and CO2 retention differently. The retention trend dependence on depth was not monotonic—optimal retention relative to the amount of injected CO2 could be achieved at middle depths and mediocre permeability as well. Results reflecting different reservoir conditions and injection strategies are shown, and analysis including the utilization factor and the net present value was conducted to examine the feasibility of different scenarios. The analysis presented in this paper can serve as a guideline for multiparameter analysis and optimization of CO2-enhanced oil recovery (EOR) with a WAG injection strategy.

Fractional flow analysis confirms the advantages of surfactant alternative gas injection (SAG) in enhanced oil recovery, but an adsorption phenomenon that has been affected by several factors, weakens the effectiveness of SAG injection. In this study, the effects of sacrificial agent, gas phase, and surfactant concentration on adsorption density on silica mineral were investigated by static and dynamic adsorption experiments. A series of SAG tests were performed to examine the effect of injection rates and presence of Calcium Lignosulfonate (CLS) on oil recovery. Also, variation of effluent sodium dodecyl sulfate (SDS) concentration during SAG test was examined. Spectrophotometric method based on the formation of an ion-pair was used in all experiments for determination of SDS concentration. The results of adsorption experiments show that SDS adsorption density on silica was reduced when nitrogen was imposed instead of using methane. It can be reduced with addition of CLS as sacrificial agents and amount of adsorption reduction increases as concentration increases. Flooding experiment results show that SAG injection increase ultimate recovery up to 10% in comparison with water alternative gas (WAG) injection. Increasing viscosity of gas phase and its trapping in porous media results a decrease in the mobility of gas and an increase in oil recovery. Stability of formed foam in porous media is rate-depended and higher SDS adsorption was observed at first cycle of SAG injection due to high solid/liquid interaction. Using CLS slightly increases the ultimate oil recovery, while it decreases the adsorption density of SDS about 22 percent during the SAG test.

Several researchers have proposed that mobility control mechanisms can positively contribute to oil recovery in the case of emulsions generated in Enhanced-Oil Recovery (EOR) operations. Chemical EOR techniques that use alkaline components or/and surfactants are known to produce undesirable emulsions that create operational problems and are difficult to break. Other water-based methods have been less studied in this sense. EOR processes such as polymer flooding and LoSalTM injection require adjustments of water chemistry, mainly by lowering the ionic strength of the solution or by decreasing hardness. The decreased ionic strength of EOR solutions can give rise to more stable water-in-oil emulsions, which are speculated to improve mobility ratio between the injectant and the displaced oil. The first step toward understanding the connection between the emulsions and EOR mechanisms is to show that EOR conditions, such as salinity and hardness requirements, among others, are conducive to stabilizing emulsions. In order to do this, adequate stability proxies are required. This paper reviews commonly used emulsion stability proxies and explains the advantages and disadvantage of methods reviewed. This paper also reviews aqueous-based EOR processes with focus on heavy oil to contextualize in-situ emulsion stabilization conditions. This context sets the basis for comparison of emulsion stability proxies.

Graphene oxide, nanographene oxide and partially reduced graphene oxide have been studied as possible foam stabilizing agents for CO2 based enhanced oil recovery. Graphene oxide was able to stabilize CO2/synthetic sea water foams, while nanographene oxide and partially reduced graphene oxide were not able to stabilize foams. The inability of nanographene oxide for stabilizing foams was explained by the increase of hydrophilicity due to size decrease, while for partially reduced graphene oxide, the high degree of reduction of the material was considered to be the reason. Graphene oxide brine dispersions showed immediate gel formation, which improved foam stability. Particle growth due to layer stacking was also observed. This mechanism was detrimental for foam stabilization. Gel formation and particle growth caused these particles to block pores and not being filterable. The work indicates that the particles studied are not suitable for CO2 enhanced oil recovery purposes.