Waxy crude oil emulsion has thixotropic properties at the temperature near gel point,which is a macromechanical characterization of the structure failure and recovery of waxy crude oil emulsion.In this paper,the thixo...Waxy crude oil emulsion has thixotropic properties at the temperature near gel point,which is a macromechanical characterization of the structure failure and recovery of waxy crude oil emulsion.In this paper,the thixotropic behaviors of waxy crude oil emulsion near gel point were studied using hysteresis loop formed by stress linear increase and decrease,as well as the structural recovery characteristics.The influence of the loading conditions and water content on the thixotropy of waxy crude oil emulsion were analyzed with hysteresis loop area.The concept of"structural recovery"was introduced to study the degree of structural recovery after different stewing,and influencing factors were taken into account.Results have shown that for waxy crude oil emulsion,the failure to fully restore of the structure after lysis is the cause of the formation of hysteresis loop,and the loading conditions will not affect the strength of thixotropy and the degree of structural recovery.Additionally,the dispersed phase droplets weaken the thixotropy and structure recovery characteristics of waxy crude oil emulsion,and the greater the water content,the weaker the thixotropy.The findings can help to better understand the safe and economic operation of waxy crude oil-water pipeline transportation.展开更多
An improved rheo-optic in situ synchronous measurement system was employed to investigate the gelation behaviour and mechanism of waxy crude oil emulsions. By combining transmitted natural light and reflected polarize...An improved rheo-optic in situ synchronous measurement system was employed to investigate the gelation behaviour and mechanism of waxy crude oil emulsions. By combining transmitted natural light and reflected polarized light microscopy, a multiangle composite light source was built to achieve the simultaneous observation of wax crystals and emulsified water droplets, as well as their dynamic aggregation process. Main outcomes on the microscopic mechanism were obtained by developed microscopic image processing method. It was found that the microstructure of W/O waxy crude oil emulsion has the evolution of “individual structure--homogeneous aggregate structure--heterogeneous coaggregate structure--floc structure” during the static cooling, which results in the four stages during gelation process. Different from previous studies, the aggregation of emulsified water droplets was found to be more significant and contributes to the formation and development of the wax crystals-emulsified water droplets coaggregate, which plays a decisive role in the further evolution of the gelled microstructure. Time series microscopic images show the dynamic aggregation of emulsified water droplets and wax crystals. Two different aggregation behaviours between wax crystals and water droplets were observed. That wax crystals can not only embed in gaps between adjacent water droplets and enhance the structure, but also surround the outside of the water droplets and continue to grow resulting in the interconnection of different coaggregates to form a larger floc structure. In addition, correlation between viscoelasticity and microstructure evolution of waxy crude oil emulsions of different water contents was discussed. With increasing water contents, the microstructure is changed from wax crystal flocculation structure as the main skeleton and the emulsified water droplets embedded in it, into the aggregation of emulsified water droplets occupying the main position. When the number of wax crystals and water droplets reaches a certain ratio, did wax crystals form coaggregates with emulsified water droplets, and the remaining wax crystals formed an overall flocculation structure, the viscoelasticity of the waxy crude oil emulsion is the highest.展开更多
In this work, the influence of the dissolution of methane(CH_(4)) gas on the wax crystal of waxy crude oil and the effect on the rheology of crude oil by dissolved CH_(4) were studied comprehensively. A self-deign hig...In this work, the influence of the dissolution of methane(CH_(4)) gas on the wax crystal of waxy crude oil and the effect on the rheology of crude oil by dissolved CH_(4) were studied comprehensively. A self-deign high-pressure micro visualization device was developed to analyze wax crystals before and after gas dissolution. The crude oil from Shengli and Nanyang was tested by the device under various gas pressures. Results showed that the viscosity, maximum shear stress and equilibrium shear stress of Shengli crude oil decreased with the increasing pressure of the dissolved CH_(4). Due to the supersaturation of dissolved gas, the viscosity, maximum shear stress and equilibrium shear stress of Nanyang crude oil decreased initially and increased with the increasing pressure of dissolved CH_(4). The change in rheology of the dissolved gas crude oil can be a combined influence of gas pressure and dissolution mechanisms caused by CH_(4). Additionally, the wax precipitation point of Shengli crude oil decreased at the saturated dissolution of CH_(4), while Nanyang crude oil showed an increasing wax precipitation temperature.Notably, the wax precipitation area, number of wax particles, and average diameter of wax crystal in both crude oils gradually decreased with dissolution. However, a saturation of CH_(4) caused a small amount of precipitation of wax crystals in Nanyang crude oil, and the small wax crystals were aggregated to form the large wax crystals. The dissolution of CH_(4) gas can affect the wax crystallization process, crystallization ability, and morphology of wax crystals that resulted in significant variation in the rheology of crude oil.展开更多
The nanocomposite EVAL-CNT was produced by chemical grafting in the solution system through the esterification of ethylene-vinyl alcohol copolymer (EVAL) and carboxylated multi-walled carbon nanotubes (O-MWCNT), and i...The nanocomposite EVAL-CNT was produced by chemical grafting in the solution system through the esterification of ethylene-vinyl alcohol copolymer (EVAL) and carboxylated multi-walled carbon nanotubes (O-MWCNT), and its structural properties were characterized. The improvement of the rheological properties of the waxy oil system by the novel pour point depressant was investigated using macroscopic rheological measurements and microscopic observations. The results showed that EVAL-CNT nanocomposite pour point depressant (PPD) could significantly reduce the pour point and improve the low temperature fluidity of crude oil and had better performance than EVAL-GO at the same addition level. The best effect was achieved at the dosing concentration of 400 ppm, which reduced the pour point by 13 ℃ and the low-temperature viscosity by 85.4%. The nanocomposites dispersed in the oil phase influenced the precipitation and crystallization of wax molecules through heterogeneous crystallization templates, which led to the increase of wax crystal size and compact structure and changed the wax crystal morphology, which had a better effect on the rheological properties of waxy oil.展开更多
This paper investigated the effects of pre-heating treatment temperatures(T_(pre))on the flowability and wax deposition characteristics of a typical waxy crude oil after adding wax inhibitors.It is found that there is...This paper investigated the effects of pre-heating treatment temperatures(T_(pre))on the flowability and wax deposition characteristics of a typical waxy crude oil after adding wax inhibitors.It is found that there is little difference in wax precipitation exothermic characteristics of crude oils at different T_(pre),as well as the wax crystal solubility coefficient in the temperature range of 25-30℃.For the undoped crude oil,the flowability after wax precipitation gets much improved and the wax deposition is alleviated as T_(pre)increasing.At T_(pre)=50℃,the viscosity and wax deposition rate of crude oil adding wax inhibitors are higher than those of the undoped crude oil.When the T_(pre)increases to 60,70,and 80℃,the flowability of the doped crude oil are largely improved and the wax deposition is suppressed with the T_(pre)increase,but the wax content of wax deposit increases gradually.It is speculated that,on the one hand,the T_(pre)increase helps the dispersion of asphaltenes into smaller sizes,which facilitates the co-crystallization with paraffin waxes and generates more aggregated wax crystal flocs.This weakens the low-temperature gel structure and increases the solid concentration required for the crosslink to form the wax deposit.On the other hand,the decrease in viscosity increases the diffusion rate of wax molecules and accelerates the aging of wax deposits.The experimental results have important guiding significance for the pipeline transportation of doped crude oils.展开更多
Yielding behaviors of waxy crude oil is one of the key issues of flow assurance challenges. The yielding of waxy crude under constant stress is actually a creep process of strain accumulation to structural failure,to ...Yielding behaviors of waxy crude oil is one of the key issues of flow assurance challenges. The yielding of waxy crude under constant stress is actually a creep process of strain accumulation to structural failure,to describe the process completely and accurately is the basis of numerical simulation of restart process of the pipeline. The creep and yield behaviors of two gelled waxy crudes were investigated experimentally under different constant applied stresses. The results clearly show that the creep process of waxy crude is related to the applied stress and time. The greater the applied stress, and the longer the loaded time, the more obvious the nonlinear features. Based on the fractional calculus theory, a fractional viscous element was developed to describe the decelerated and steady creep process of gelled waxy crude. On the basis of the damage theory, an elastic damage element was proposed to describe the accelerated creep after the yielding. According to the idea of mechanical analogy, a nonlinear creep model was established by a fractional viscous element, an elastic damaged element, and an elastic element in series, which can accurately describe the whole creep and yielding process of gelled waxy crude.展开更多
Lauramine is widely considered to be an asphaltene flocculant,but its effect on the modification of crude oil by PPDs has been little studied.In this paper,the effect of LA dosage on the rheology improvement of EVA PP...Lauramine is widely considered to be an asphaltene flocculant,but its effect on the modification of crude oil by PPDs has been little studied.In this paper,the effect of LA dosage on the rheology improvement of EVA PPDs(100 ppm)on Qinghai waxy crude oil was investigated through rheological measurement,wax precipitating analysis,granularity test and resins/asphaltenes FTIR analysis.Compared with pure EVA,the compounding of LA and EVA obviously enhances the agglomeration degree and reduces the number of fine wax crystals,thus further enhancing the rheology of the oil samples,and the best performance is at the LA dosage of 200 ppm.At relatively small LA dosages,the LA facilitates the adsorption of EVA molecules on the asphaltene surfaces,which favors the becoming of EVA/asphaltenes composite particles;but at relatively high LA dosages,the LA makes the asphaltenes more aggregated and disturbs the EVA adsorption on the asphaltenes,which is adverse for the formation of EVA/asphaltenes compound particles.The compound particles can serve as wax precipitating templates and significantly influence its morphology,thus further improving the crude oil rheology.In consequence,the rheology improvement of EVA PPDs on Qinghai waxy crude oil first increases and then decreases with increasing the LA dosage.展开更多
基金supported by the Natural Science Foundation of Heilongjiang Province(Grant No.LH2020E015)the General Project of Natural Science Research in Jiangsu Universities(Grant No.20KJB440004)+1 种基金the science and technology program of Changzhou University(Grant No.ZMF18020303 and ZMF18020304)the science and technology program of Jiangsu Key Laboratory of Oil and Gas Storage&Transportation Technology(Grant No.CDYQCY201903,CDYQCY201904 and CDYQCY202003)。
文摘Waxy crude oil emulsion has thixotropic properties at the temperature near gel point,which is a macromechanical characterization of the structure failure and recovery of waxy crude oil emulsion.In this paper,the thixotropic behaviors of waxy crude oil emulsion near gel point were studied using hysteresis loop formed by stress linear increase and decrease,as well as the structural recovery characteristics.The influence of the loading conditions and water content on the thixotropy of waxy crude oil emulsion were analyzed with hysteresis loop area.The concept of"structural recovery"was introduced to study the degree of structural recovery after different stewing,and influencing factors were taken into account.Results have shown that for waxy crude oil emulsion,the failure to fully restore of the structure after lysis is the cause of the formation of hysteresis loop,and the loading conditions will not affect the strength of thixotropy and the degree of structural recovery.Additionally,the dispersed phase droplets weaken the thixotropy and structure recovery characteristics of waxy crude oil emulsion,and the greater the water content,the weaker the thixotropy.The findings can help to better understand the safe and economic operation of waxy crude oil-water pipeline transportation.
文摘An improved rheo-optic in situ synchronous measurement system was employed to investigate the gelation behaviour and mechanism of waxy crude oil emulsions. By combining transmitted natural light and reflected polarized light microscopy, a multiangle composite light source was built to achieve the simultaneous observation of wax crystals and emulsified water droplets, as well as their dynamic aggregation process. Main outcomes on the microscopic mechanism were obtained by developed microscopic image processing method. It was found that the microstructure of W/O waxy crude oil emulsion has the evolution of “individual structure--homogeneous aggregate structure--heterogeneous coaggregate structure--floc structure” during the static cooling, which results in the four stages during gelation process. Different from previous studies, the aggregation of emulsified water droplets was found to be more significant and contributes to the formation and development of the wax crystals-emulsified water droplets coaggregate, which plays a decisive role in the further evolution of the gelled microstructure. Time series microscopic images show the dynamic aggregation of emulsified water droplets and wax crystals. Two different aggregation behaviours between wax crystals and water droplets were observed. That wax crystals can not only embed in gaps between adjacent water droplets and enhance the structure, but also surround the outside of the water droplets and continue to grow resulting in the interconnection of different coaggregates to form a larger floc structure. In addition, correlation between viscoelasticity and microstructure evolution of waxy crude oil emulsions of different water contents was discussed. With increasing water contents, the microstructure is changed from wax crystal flocculation structure as the main skeleton and the emulsified water droplets embedded in it, into the aggregation of emulsified water droplets occupying the main position. When the number of wax crystals and water droplets reaches a certain ratio, did wax crystals form coaggregates with emulsified water droplets, and the remaining wax crystals formed an overall flocculation structure, the viscoelasticity of the waxy crude oil emulsion is the highest.
基金the National Natural Science Foundation of China (51774315, 51574274)the Natural Science Found of Hebei Province (E2020203013) for the support of this work。
文摘In this work, the influence of the dissolution of methane(CH_(4)) gas on the wax crystal of waxy crude oil and the effect on the rheology of crude oil by dissolved CH_(4) were studied comprehensively. A self-deign high-pressure micro visualization device was developed to analyze wax crystals before and after gas dissolution. The crude oil from Shengli and Nanyang was tested by the device under various gas pressures. Results showed that the viscosity, maximum shear stress and equilibrium shear stress of Shengli crude oil decreased with the increasing pressure of the dissolved CH_(4). Due to the supersaturation of dissolved gas, the viscosity, maximum shear stress and equilibrium shear stress of Nanyang crude oil decreased initially and increased with the increasing pressure of dissolved CH_(4). The change in rheology of the dissolved gas crude oil can be a combined influence of gas pressure and dissolution mechanisms caused by CH_(4). Additionally, the wax precipitation point of Shengli crude oil decreased at the saturated dissolution of CH_(4), while Nanyang crude oil showed an increasing wax precipitation temperature.Notably, the wax precipitation area, number of wax particles, and average diameter of wax crystal in both crude oils gradually decreased with dissolution. However, a saturation of CH_(4) caused a small amount of precipitation of wax crystals in Nanyang crude oil, and the small wax crystals were aggregated to form the large wax crystals. The dissolution of CH_(4) gas can affect the wax crystallization process, crystallization ability, and morphology of wax crystals that resulted in significant variation in the rheology of crude oil.
文摘The nanocomposite EVAL-CNT was produced by chemical grafting in the solution system through the esterification of ethylene-vinyl alcohol copolymer (EVAL) and carboxylated multi-walled carbon nanotubes (O-MWCNT), and its structural properties were characterized. The improvement of the rheological properties of the waxy oil system by the novel pour point depressant was investigated using macroscopic rheological measurements and microscopic observations. The results showed that EVAL-CNT nanocomposite pour point depressant (PPD) could significantly reduce the pour point and improve the low temperature fluidity of crude oil and had better performance than EVAL-GO at the same addition level. The best effect was achieved at the dosing concentration of 400 ppm, which reduced the pour point by 13 ℃ and the low-temperature viscosity by 85.4%. The nanocomposites dispersed in the oil phase influenced the precipitation and crystallization of wax molecules through heterogeneous crystallization templates, which led to the increase of wax crystal size and compact structure and changed the wax crystal morphology, which had a better effect on the rheological properties of waxy oil.
基金The authors thank the financial support from the National Natural Science Foundation of China(51904327,U19B2012)China University of Petroleum Innovation Project(22CX06050A).
文摘This paper investigated the effects of pre-heating treatment temperatures(T_(pre))on the flowability and wax deposition characteristics of a typical waxy crude oil after adding wax inhibitors.It is found that there is little difference in wax precipitation exothermic characteristics of crude oils at different T_(pre),as well as the wax crystal solubility coefficient in the temperature range of 25-30℃.For the undoped crude oil,the flowability after wax precipitation gets much improved and the wax deposition is alleviated as T_(pre)increasing.At T_(pre)=50℃,the viscosity and wax deposition rate of crude oil adding wax inhibitors are higher than those of the undoped crude oil.When the T_(pre)increases to 60,70,and 80℃,the flowability of the doped crude oil are largely improved and the wax deposition is suppressed with the T_(pre)increase,but the wax content of wax deposit increases gradually.It is speculated that,on the one hand,the T_(pre)increase helps the dispersion of asphaltenes into smaller sizes,which facilitates the co-crystallization with paraffin waxes and generates more aggregated wax crystal flocs.This weakens the low-temperature gel structure and increases the solid concentration required for the crosslink to form the wax deposit.On the other hand,the decrease in viscosity increases the diffusion rate of wax molecules and accelerates the aging of wax deposits.The experimental results have important guiding significance for the pipeline transportation of doped crude oils.
基金the financial support from the National Natural Science Foundation of China (No.52174066)。
文摘Yielding behaviors of waxy crude oil is one of the key issues of flow assurance challenges. The yielding of waxy crude under constant stress is actually a creep process of strain accumulation to structural failure,to describe the process completely and accurately is the basis of numerical simulation of restart process of the pipeline. The creep and yield behaviors of two gelled waxy crudes were investigated experimentally under different constant applied stresses. The results clearly show that the creep process of waxy crude is related to the applied stress and time. The greater the applied stress, and the longer the loaded time, the more obvious the nonlinear features. Based on the fractional calculus theory, a fractional viscous element was developed to describe the decelerated and steady creep process of gelled waxy crude. On the basis of the damage theory, an elastic damage element was proposed to describe the accelerated creep after the yielding. According to the idea of mechanical analogy, a nonlinear creep model was established by a fractional viscous element, an elastic damaged element, and an elastic element in series, which can accurately describe the whole creep and yielding process of gelled waxy crude.
基金financially supported by the National Natural Science Foundation of China(grant number 51774311,51904327)China Postdoctoral Science Foundation(grant number 2019TQ0354,2019M662468)。
文摘Lauramine is widely considered to be an asphaltene flocculant,but its effect on the modification of crude oil by PPDs has been little studied.In this paper,the effect of LA dosage on the rheology improvement of EVA PPDs(100 ppm)on Qinghai waxy crude oil was investigated through rheological measurement,wax precipitating analysis,granularity test and resins/asphaltenes FTIR analysis.Compared with pure EVA,the compounding of LA and EVA obviously enhances the agglomeration degree and reduces the number of fine wax crystals,thus further enhancing the rheology of the oil samples,and the best performance is at the LA dosage of 200 ppm.At relatively small LA dosages,the LA facilitates the adsorption of EVA molecules on the asphaltene surfaces,which favors the becoming of EVA/asphaltenes composite particles;but at relatively high LA dosages,the LA makes the asphaltenes more aggregated and disturbs the EVA adsorption on the asphaltenes,which is adverse for the formation of EVA/asphaltenes compound particles.The compound particles can serve as wax precipitating templates and significantly influence its morphology,thus further improving the crude oil rheology.In consequence,the rheology improvement of EVA PPDs on Qinghai waxy crude oil first increases and then decreases with increasing the LA dosage.
