Gas/water foams stabilized with a newly developed anionic surfactant for gas mobility control applications

Carbon dioxide(CO2) flooding is one of the most globally used EOR processes to enhance oil recovery.However,the low gas viscosity and density result in gas channeling and gravity override which lead to poor sweep efficiency.Foam application for mobility control is a promising technology to increase the gas viscosity,lower the mobility and improve the sweep efficiency in the reservoir.Foam is generated in the reservoir by co-injection of surfactant solutions and gas.Although there are many surfactants that can be used for such purpose,their performance with supercritical CO2(ScCO2) is weak causing poor or loss of mobility control.This experimental study evaluates a newly developed surfactant(CNF) that was introduced for ScCO2 mobility control in comparison with a common foaming agent,anionic alpha olefin sulfonate(AOS) surfactant.Experimental work was divided into three stages:foam static tests,interfacial tension measurements,and foam dynamic tests.Both surfactants were investigated at different conditions.In general,results show that both surfactants are good foaming agents to reduce the mobility of ScCO2 with better performance of CNF surfactant.Shaking tests in the presence of crude oil show that the foam life for CNF extends to more than 24 h but less than that for AOS.Moreover,CNF features lower critical micelle concentration(CMC),higher adsorption,and smaller area/molecule at the liquid-air interface.Furthermore,entering,spreading,and bridging coefficients indicate that CNF surfactant produces very stable foam with light crude oil in both deionized and saline water,whereas AOS was stable only in deionized water.At all conditions for mobility reduction evaluation,CNF exhibits stronger flow resistance,higher foam viscosity,and higher mobility reduction factor than that of AOS surfactant.In addition,CNF and ScCO2 simultaneous injection produced 8.83% higher oil recovery than that of the baseline experiment and 7.87% higher than that of AOS.Pressure drop profiles for foam flooding using CNF was slightly higher than that of AOS indicating that CNF is better in terms of foam-oil tolerance which resulted in higher oil recovery.

Enhancement of a foaming formulation with a zwitterionic surfactant for gas mobility control in harsh reservoir conditions

This work presents the design of a robust foam formulation that tolerates harsh reservoir conditions(high salinity,high divalent ion concentration,high temperature,light oil,and hydrocarbon injection gas)in a sandstone reservoir.For this,we selected anionic Alpha Olefin Sulfonate(AOS)surfactants and studied their synergistic effects in mixtures with zwitterionic betaines to enhance foam performance.The laboratory workflow used to define the best formulation followed a de-risking approach in three consecutive phases.First,(phase 1)the main surfactant(AOS)was selected among a series of commercial candidates in static conditions.Then,(phase 2)the betaine booster to be combined with the previously selected AOS was chosen and their ratio optimized in static conditions.Subsequently,(phase 3)the surfactant/booster ratio was optimized under dynamic conditions in a porous medium in the absence and the presence of oil.As a result of this study,a mixture of an AOS C14-C16 and cocamidopropyl hydroxysultaine(CAPHS)was selected as the one having the best performance.The designed formulation was proven to be robust in a wide range of conditions.It generated a strong and stable foam at reservoir conditions,overcoming variations in salinity and foam quality,and tolerated the presence of oil.

Foaming supramolecular surfactants for gas mobility control in naturally fractured carbonate reservoirs at high temperature,salinity,and hardness

Oil production and mainte nance are essential issues in naturally fractured reservoirs because they are the largest and most productive on earth.However,they present early water and gas channeling but could be remediated by using foaming agents to control these phenomena through blocking channeling areas.In Mexico these reservoirs have pressure up to 5,500 psi,high temperature up to 200℃,salinity up to400,000 ppm,and hardness up to 250,000 ppm;due to these thermodynamic conditions,there has been no available technology to form stable enough foams.In this work,a foaming supramolecular surfactant with the capability to chelate Ca^(2+)ions is examined.As a result,surfactant monomers are bridged by captured Ca^(2+)cations leading to the formation of high-molecular-weight oligomers,which significantly increment the viscosity of the solution improving the foam stability,and since at this manner the Ca2+cations are no longer available to precipitate as components of solid salts,the foaming supramolecular surfactant also performs as antiscalant.These observations are explained through quantum theoretical modeling.The foam is stable,effectively blocking the gas channels,whereas in presence of oil the foam is broken leading the oil to pass into the wellbore.The characteristic rheological properties of the foam allow its injection into the formation at a range of flow rates,foam qualities,and shear stress to achieve the flooding and the blocking of a variety of fractured carbonate formations,and the change of the wettability of the matrix,which is a desirable behavior in a huff and puff process,as reported in a previous publication about a successful pilot test of this foam.

A review of recent developments in CO_(2) mobility control in enhanced oil recovery

Carbon dioxide-enhanced oil recovery(CO_(2)-EOR)has gained widespread attention in light of the declining conventional oil reserves.Moreover,CO_(2)-EOR contributes to the reduction of the global emissions of greenhouse gases through CO_(2) 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,CO_(2) is used in a continuous flooding scheme for EOR.However,continuous CO_(2) flooding tends to be problematic due to unfavorable mobility,viscous fingering/channeling and early breakthrough of CO_(2),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 CO_(2)water-alternating-gas(WAG)injection,polymer-assisted CO_(2) injection,surfactant-assisted CO_(2) mobility control(CO_(2)-foam injection),and nanoparticle-assisted CO_(2) flooding.Each method addresses,to an extent,one or more of the problems associated with conventional CO_(2) flooding.Furthermore,incorporating more than one method can provide better performance in terms of CO_(2) mobility control and oil recovery.In comparison with CO_(2)-WAG and CO_(2)-foam injection methods,the use of polymers and nanoparticles with CO_(2) 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.

Robot-Oriented 6G Satellite-UAV Networks: Requirements, Paradigm Shifts, and Case Studies

Networked robots can perceive their surroundings, interact with each other or humans,and make decisions to accomplish specified tasks in remote/hazardous/complex environments. Satelliteunmanned aerial vehicle(UAV) networks can support such robots by providing on-demand communication services. However, under traditional open-loop communication paradigm, the network resources are usually divided into user-wise mostly-independent links,via ignoring the task-level dependency of robot collaboration. Thus, it is imperative to develop a new communication paradigm, taking into account the highlevel content and values behind, to facilitate multirobot operation. Inspired by Wiener’s Cybernetics theory, this article explores a closed-loop communication paradigm for the robot-oriented satellite-UAV network. This paradigm turns to handle group-wise structured links, so as to allocate resources in a taskoriented manner. It could also exploit the mobility of robots to liberate the network from full coverage,enabling new orchestration between network serving and positive mobility control of robots. Moreover,the integration of sensing, communications, computing and control would enlarge the benefit of this new paradigm. We present a case study for joint mobile edge computing(MEC) offloading and mobility control of robots, and finally outline potential challenges and open issues.

Interaction of Foam and Microemulsion Components in Low-Tension-Gas Flooding

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.

Necessity and feasibility of improving the residual resistance factor of polymer flooding in heavy oil reservoirs

The efficiency of water flooding in heavy oil reservoirs would be improved by increasing the viscosity of the displacing phase, but the sweep efficiency is not of significance due to the low mobility of the vicious oil. On the basis of mobility control theory, increasing the residual resistance factor not only reduces the water-oil mobility ratio but also decreases the requirement for viscosity enhancement of the polymer solution. The residual resistance factor caused by hydrophobic associating polymer solution is higher than that caused by polyacrylamide solution in brine containing high concentrations of calcium and magnesium ions. The results of numerical simulations show that the polymer flooding efficiency improved by increasing the residual resistance factor is far better than that by only increasing solution viscosity. The recovery factor of heavy oil reservoirs （70 mPa·s） can be enhanced by hydrophobic associating polymer solution of high residual resistance factor （more than 3） and high effective viscosity （24 mPa·s）. Therefore, increasing the residual resistance factor of the polymer solution not only decreases the requirement for the viscosity of polymer solution injected into heavy oil reservoirs but also is favorable to enhanced oil recovery during polymer flooding.

Examination of literature on colloidal dispersion gels for oil recovery

This paper examines literature that claims,suggests,or implies that floods with"colloidal dispersion gels"(CDGs)are superior to polymer floods for oil recovery.The motivation for this report is simple.If CDGs can propagate deep into the porous rock of a reservoir,and at the same time,provide resistance factors or residual resistance factors that are greater than those for the same polymer formulation without the crosslinker,then CDGs should be used in place of polymer solutions for most/all polymer,surfactant,and ASP floods.In contrast,if the claims are not valid,(1)money spent on crosslinker in the CDG formulations was wasted,(2)the mobility reduction/mobility control for CDG field projects was under-designed,and(3)reservoir performance could have been damaged by excessive loss of polymer,face-plugging by gels,and/or excessive fracture extension.From this review,the clear answer is that there is no credible evidence that colloidal dispersion gels can propagate deep into the porous rock of a reservoir,and at the same time,provide resistance factors or residual resistance factors that are greater than those for the same polymer formulation without the crosslinker.CDGs have been sold using a number of misleading and invalid arguments.Very commonly,Hall plots are claimed to demonstrate that CDGs provide higher resistance factors and/or residual resistance factors than normal polymer solutions.However,because Hall plots only monitor injection pressures at the wellbore,they reflect the composite of face plugging/formation damage,in-situ mobility changes,and fracture extension.Hall plots cannot distinguish between these effects-so they cannot quantify in situ resistance factors or residual resistance factors.Laboratory studiesdwhere CDG gelants were forced through short cores during 2-3 h-have incorrectly been cited as proof that CDGs will propagate deep(hundreds of feet)into the porous rock of a reservoir over the course of months.In contrast,most legitimate laboratory studies reveal that the gelation time for CDGs is a day or less and that CDGs will not propagate through porous rock after gelation.A few cases were noted where highly depleted Al and/or HPAM fluids passed through cores after one week of aging.Details about these particular formulations/experiments were sparse and questions remain about their reproducibility.No credible evidence indicates that the CDG can propagate deep into a reservoir(over the course of weeks or months)and still provide a greater effect than that from the polymer alone.With one exception,aluminum from the CDG was never reported to be produced in a field application.In the exception,Chang reported producing 1-20%of the injected aluminum concentration.The available evidence suggests that some free(unreacted)HPAM and aluminum that was associated with the original CDG can propagate through porous media.However,there is no evidence that this HPAM or aluminum provides mobility reduction greater than that for the polymer formulation without crosslinker.

Experimental investigation on using CO_(2)/H_(2)O emulsion with high water cut in enhanced oil recovery

CO_(2) emulsions used for EOR have received a lot of interest because of its good performance on CO_(2)mobility reduction.However,most of them have been focusing on the high quality CO_(2) emulsion(high CO_(2) fraction),while CO_(2) emulsion with high water cut has been rarely researched.In this paper,we carried out a comprehensive experimental study of using high water cut CO_(2)/H_(2)O emulsion for enhancing oil recovery.Firstly,a nonionic surfactant,alkyl glycosides(APG),was selected to stabilize CO_(2)/H_(2)O emulsion,and the corresponding morphology and stability were evaluated with a transparent PVT cell.Subsequently,plugging capacity and apparent viscosity of CO_(2)/H_(2)O emulsion were measured systematically by a sand pack displacement apparatus connected with a 1.95-m long capillary tube.Furthermore,a high water cut(40 vol%) CO_(2)/H_(2)O emulsion was selected for flooding experiments in a long sand pack and a core sample,and the oil recovery,the rate of oil recovery,and the pressure gradients were analyzed.The results indicated that APG had a good performance on emulsifying and stabilizing CO_(2) emulsion.An inversion from H_(2)O/CO_(2) emulsion to CO_(2)/H_(2)O emulsion with the increase in water cut was confirmed.CO_(2)/H_(2)O emulsions with lower water cuts presented higher apparent viscosity,while the optimal plugging capacity of CO_(2)/H_(2)O emulsion occurred at a certain water cut.Eventually,the displacement using CO_(2)/H_(2)O emulsion provided 18.98% and 13.36% additional oil recovery than that using pure CO_(2) in long sand pack and core tests,respectively.This work may provide guidelines for EOR using CO_(2) emulsions with high water cut.

High-performance multilayer WSe2 field-effect transistors with carrier type control

In this stud high-performance multilayer WSe2 field-effect transistor （FET） devices with carrier type control are demonstrated via thickness modulation and a remote oxygen plasma surface treatment. Carrier type control in multilayer WSe2 FET devices with Cr/Au contacts is initially demonstrated by modulating the WSe2 thickness. The carrier type evolves with increasing WSe2 channel thickness, being p-type, ambipolar, and n-type at thicknesses 〈 3, - 4, and 〉 5 nm, respectively. The thickness-dependent carrier type is attributed to changes in the bandgap of WSe2 as a function of the thickness and the carrier band offsets relative to the metal contacts. Furthermore, we present a strong hole carrier doping effect via remote oxygen plasma treatment. It non-degenerately converts n-type characteristics into p-type and enhances field-effect hole mobility by three orders of magnitude. This work demonstrates progress towards the realization of high-performance multilayer WSe2 FETs with carrier type control, potentially extendable to other transition metal dichalcogenides, for future electronic and oDtoelectronic alpplications.

Review on chemical enhanced oil recovery using polymer flooding: Fundamentals, experimental and numerical simulation

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.

A Flocking-Based on Demand Routing Protocol for Unmanned Aerial Vehicles

The interest shown by some community of researchers to autonomous drones or UAVs （unmanned aerial vehicles） has increased with the advent of wireless communication networks. These networks allow UAVs to cooperate more efficiently in an ad hoc manner in order to achieve specific tasks in specific environments. To do so, each drone navigates autonomously while staying connected with other nodes in its group via radio links. This connectivity can deliberately be maintained for a while constraining the mobility of the drones. This will be suitable for the drones involved in a given path of a given transmission between a source and a destination. This constraint could be removed at the end of the transmission process and the mobility of each concerned drone becomes again independent from the others. In this work, we proposed a flocking-based routing protocol for UAVs called BR-AODV. The protocol takes advantage of a well known ad hoc routing protocol for on-demand route computation, and the Boids of Reynolds mechanism for connectivity and route maintaining while data is being transmitted. Moreover, an automatic ground base stations discovery mechanism has been introduced for a proactive drones and ground networks association needed for the context of real-time applications. The performance of BR-AODV was evaluated and compared with that of classical AODV routing protocol and the results show that BR-AODV outperforms AODV in terms of delay, throughput and packet loss.

Power Adjusting Algorithm： A New Cross-Layer Power Saving Mechanism for Mobile Ad-Hoc Networks

Power saving is one of the key issues in Mobile Ad-Hoc Networks （MANETs）. It can be realized in Medium Access Control （MAC） layer and network layer. However, previous attentions were mainly paid to MAC layer or network layer with the aim of improving the channel utilization by adopting variable-range transmission power control. In this paper we focus on the power saving in both MAC layer and network layer, and propose a Power Adjusting Algorithm （PAA）. In the presence of host＇s mobility, PAA is designed to conserve energy by adjusting the transmission power to maintain the route＇s connectivity and restarting the route discovery periodically to find a new route with better energy efficiency dynamically. After analyzing the operations of PAA, we find that the length of route discovery restarting period is a critical argument which will affect power saving, and an energy consumption model is abstracted to find the optimal value of the restarting period by analyzing the energy consumption of this algorithm. PAA can handle the mobility of MANET by adjusting the transmission power and in the meantime save energy by restarting route discovery periodically to balance the energy consumption on route discovery and packet delivering. Simulation results show that, PAA saves nearly 40% energy compared with Dynamic Source Routing protocol when the maximum speed of mobile hosts is larger than 8 m/s.