Hydrogels are widely used in reservoir flow control to enhanced oil recovery.However,challenges such as environmental contamination from conventional crosslinkers,poor solubility of crosslinking agents,and short gelat...Hydrogels are widely used in reservoir flow control to enhanced oil recovery.However,challenges such as environmental contamination from conventional crosslinkers,poor solubility of crosslinking agents,and short gelation times under high-temperature conditions(e.g.,150℃)have hindered their practical application.Herein,we present the synthesis of amine-functionalized carbon quantum dots(NH_(2)-CQDs),which act as both a nano-crosslinker and a nano-reinforcing agent within hydrogel systems.The NH_(2)-CQDs-incorporated hydrogel can remain stability for 300 days under the conditions of a mineralization degree of 2.11×10^(4)mg/mL and 170℃,and has high tensile strength(371 kPa),good toughness(49.6 kJ/m~3),excellent viscoelasticity(G'=960 Pa,G"=460 Pa)and shear resistance.In addition,NH_(2)-CQDs adds many hydroxyl groups to the hydrogel,which can be attached to the surface of various substances.At the same time,micro-nano capsules containing NH_(2)-CQDs were formed by self-assembly of hydrophobic SiO_(2)on water droplets,the NH_(2)-CQDs solution is encapsulated in a capsule,and when stimulated by external conditions(temperature,pH,surfactant),the capsule releases the NH_(2)-CQDs solution,this method greatly delays the crosslinking time between polymer and crosslinker at high temperature.Under the condition of 170℃and pH=7,the gelation time of 10%hydrophobic SiO_(2)coated hydrogel is 44 times that of uncoated hydrogel,which can be effectively used for deep formation flow control,and CQD give hydrogels fluorescence properties that can be used for underground signal tracking.展开更多
Current interest in deep,low-permeability formations(<10 md)demands accelerated development of high-temperature hydraulic fracturing technologies.Conventional guar systems break down above 300°F and require hi...Current interest in deep,low-permeability formations(<10 md)demands accelerated development of high-temperature hydraulic fracturing technologies.Conventional guar systems break down above 300°F and require higher polymer loadings to maintain thermal stability.However,higher polymer loadings generate more residue and damage to the proppant pack and the formation.To resolve these problems,a variety of high-temperature stabilizers are added to enhance the thermal stability of these fracturing fluids at temperatures above 300F.The focus of this work is to:(1)identify those additives that best enhance temperature stability of fracturing fluids and(2)study the rheological influence of incorporating these additives on the fracturing fluid systems.The experimental fracturing-fluid solutions were prepared at a total polymer concentration of 30 and 40 lb/1000 gal.Additives such as synthetic polymer,oxygen scavengers,crosslinkers,crosslinker delay additives,and pH buffers were examined in this work.Hydrated polymer solutions were crosslinked with a metallic crosslinker between 200 and 400°F.Viscosity measurements were carried out in a highpressure/high-temperature(HP/HT)rheometer to evaluate rheology and thermal stability.Results show that adding a synthetic polymer and a crosslinker with the slowest reaction rate improves the fracturing fluid thermal stability.Of the three other additives tested,oxygen scavengers showed the greatest enhancement to thermal stability while pH buffers showed the least.Through the addition of high-temperature stabilizing additives,the fracturing fluid in this work was able to maintain a stable performance at temperatures up to 400°F.Maintaining the thermal stability of fracturing fluids at a lower polymer loading remains a challenge in the industry.This work proposes techniques that can be used to enhance the thermal stability of fracturing fluids.Deeper knowledge about these different techniques will allow for better additive development and application in the field.展开更多
基金support and funding from the National Natural Science Foundation of China(No.52174047)。
文摘Hydrogels are widely used in reservoir flow control to enhanced oil recovery.However,challenges such as environmental contamination from conventional crosslinkers,poor solubility of crosslinking agents,and short gelation times under high-temperature conditions(e.g.,150℃)have hindered their practical application.Herein,we present the synthesis of amine-functionalized carbon quantum dots(NH_(2)-CQDs),which act as both a nano-crosslinker and a nano-reinforcing agent within hydrogel systems.The NH_(2)-CQDs-incorporated hydrogel can remain stability for 300 days under the conditions of a mineralization degree of 2.11×10^(4)mg/mL and 170℃,and has high tensile strength(371 kPa),good toughness(49.6 kJ/m~3),excellent viscoelasticity(G'=960 Pa,G"=460 Pa)and shear resistance.In addition,NH_(2)-CQDs adds many hydroxyl groups to the hydrogel,which can be attached to the surface of various substances.At the same time,micro-nano capsules containing NH_(2)-CQDs were formed by self-assembly of hydrophobic SiO_(2)on water droplets,the NH_(2)-CQDs solution is encapsulated in a capsule,and when stimulated by external conditions(temperature,pH,surfactant),the capsule releases the NH_(2)-CQDs solution,this method greatly delays the crosslinking time between polymer and crosslinker at high temperature.Under the condition of 170℃and pH=7,the gelation time of 10%hydrophobic SiO_(2)coated hydrogel is 44 times that of uncoated hydrogel,which can be effectively used for deep formation flow control,and CQD give hydrogels fluorescence properties that can be used for underground signal tracking.
基金The authors thank Gia Alexander for editorial assistance in preparing this paper.
文摘Current interest in deep,low-permeability formations(<10 md)demands accelerated development of high-temperature hydraulic fracturing technologies.Conventional guar systems break down above 300°F and require higher polymer loadings to maintain thermal stability.However,higher polymer loadings generate more residue and damage to the proppant pack and the formation.To resolve these problems,a variety of high-temperature stabilizers are added to enhance the thermal stability of these fracturing fluids at temperatures above 300F.The focus of this work is to:(1)identify those additives that best enhance temperature stability of fracturing fluids and(2)study the rheological influence of incorporating these additives on the fracturing fluid systems.The experimental fracturing-fluid solutions were prepared at a total polymer concentration of 30 and 40 lb/1000 gal.Additives such as synthetic polymer,oxygen scavengers,crosslinkers,crosslinker delay additives,and pH buffers were examined in this work.Hydrated polymer solutions were crosslinked with a metallic crosslinker between 200 and 400°F.Viscosity measurements were carried out in a highpressure/high-temperature(HP/HT)rheometer to evaluate rheology and thermal stability.Results show that adding a synthetic polymer and a crosslinker with the slowest reaction rate improves the fracturing fluid thermal stability.Of the three other additives tested,oxygen scavengers showed the greatest enhancement to thermal stability while pH buffers showed the least.Through the addition of high-temperature stabilizing additives,the fracturing fluid in this work was able to maintain a stable performance at temperatures up to 400°F.Maintaining the thermal stability of fracturing fluids at a lower polymer loading remains a challenge in the industry.This work proposes techniques that can be used to enhance the thermal stability of fracturing fluids.Deeper knowledge about these different techniques will allow for better additive development and application in the field.
