Polymer flooding in fractured wells has been extensively applied in oilfields to enhance oil recovery.In contrast to water,polymer solution exhibits non-Newtonian and nonlinear behavior such as effects of shear thinni...Polymer flooding in fractured wells has been extensively applied in oilfields to enhance oil recovery.In contrast to water,polymer solution exhibits non-Newtonian and nonlinear behavior such as effects of shear thinning and shear thickening,polymer convection,diffusion,adsorption retention,inaccessible pore volume and reduced effective permeability.Meanwhile,the flux density and fracture conductivity along the hydraulic fracture are generally non-uniform due to the effects of pressure distribution,formation damage,and proppant breakage.In this paper,we present an oil-water two-phase flow model that captures these complex non-Newtonian and nonlinear behavior,and non-uniform fracture characteristics in fractured polymer flooding.The hydraulic fracture is firstly divided into two parts:high-conductivity fracture near the wellbore and low-conductivity fracture in the far-wellbore section.A hybrid grid system,including perpendicular bisection(PEBI)and Cartesian grid,is applied to discrete the partial differential flow equations,and the local grid refinement method is applied in the near-wellbore region to accurately calculate the pressure distribution and shear rate of polymer solution.The combination of polymer behavior characterizations and numerical flow simulations are applied,resulting in the calculation for the distribution of water saturation,polymer concentration and reservoir pressure.Compared with the polymer flooding well with uniform fracture conductivity,this non-uniform fracture conductivity model exhibits the larger pressure difference,and the shorter bilinear flow period due to the decrease of fracture flow ability in the far-wellbore section.The field case of the fall-off test demonstrates that the proposed method characterizes fracture characteristics more accurately,and yields fracture half-lengths that better match engineering reality,enabling a quantitative segmented characterization of the near-wellbore section with high fracture conductivity and the far-wellbore section with low fracture conductivity.The novelty of this paper is the analysis of pressure performances caused by the fracture dynamics and polymer rheology,as well as an analysis method that derives formation and fracture parameters based on the pressure and its derivative curves.展开更多
The oil-water two-phase flow pressure-transient analysis model for polymer flooding fractured well is established by considering the comprehensive effects of polymer shear thinning,shear thickening,convection,diffusio...The oil-water two-phase flow pressure-transient analysis model for polymer flooding fractured well is established by considering the comprehensive effects of polymer shear thinning,shear thickening,convection,diffusion,adsorption retention,inaccessible pore volume and effective permeability reduction.The finite volume difference and Newton iteration methods are applied to solve the model,and the effects of fracture conductivity coefficient,injected polymer mass concentration,initial polymer mass concentration and water saturation on the well-test type curves of polymer flooding fractured wells are discussed.The results show that with the increase of fracture conductivity coefficient,the pressure conduction becomes faster and the pressure drop becomes smaller,so the pressure curve of transitional flow goes downward,the duration of bilinear flow becomes shorter,and the linear flow appears earlier and lasts longer.As the injected polymer mass concentration increases,the effective water phase viscosity increases,and the pressure loss increases,so the pressure and pressure derivative curves go upward,and the bilinear flow segment becomes shorter.As the initial polymer mass concentration increases,the effective water phase viscosity increases,so the pressure curve after the wellbore storage segment moves upward as a whole.As the water saturation increases,the relative permeability of water increases,the relative permeability of oil decreases,the total oil-water two-phase mobility becomes larger,and the pressure loss is reduced,so the pressure curve after the wellbore storage segment moves downward as a whole.The reliability and practicability of this new model are verified by the comparison of the results from simplified model and commercial well test software,and the actual well test data.展开更多
This review presents our perspective on the factors that have brought polymer flooding to its current state. Insights are provided on why HPAM is the dominant polymer used as well as what is needed to make alternative...This review presents our perspective on the factors that have brought polymer flooding to its current state. Insights are provided on why HPAM is the dominant polymer used as well as what is needed to make alternative polymers and mobility-control methods viable. Explanation is given for why large polymer banks are needed for polymer flooding, and design of the injected polymer viscosity is detailed for cases with/without crossflow. The role of fractures and horizontal wells are discussed for improving injectivity and extending polymer flooding to recover oils with viscosities as high as 10,000 cP. Operational improvements are described to minimize mechanical and oxidative stability to allow HPAM polymers to be viable to 70 °C and ATBS polymers to 120 °C. Key factors affecting polymer retention are summarized. The paper points out unresolved issues and future directions for polymer flooding.展开更多
At present, the polymer solution is usually assumed to be Newtonian fluid or pseudoplastic fluid, and its elasticity is not considered on the study of polymer flooding well testing model. A large number of experiments...At present, the polymer solution is usually assumed to be Newtonian fluid or pseudoplastic fluid, and its elasticity is not considered on the study of polymer flooding well testing model. A large number of experiments have shown that polymer solutions have viscoelasticity, and disregarding the elasticity will cause certain errors in the analysis of polymer solution seepage law. Based on the percolation theory, this paper describes the polymer flooding mechanism from the two aspects of viscous effect and elastic effect, the mathematical model of oil water two-phase three components unsteady flow in viscoelastic polymer flooding was established, and solved by finite difference method, and the well-test curve was drawn to analyze the rule of well test curve in polymer flooding. The results show that, the degree of upward warping in the radial flow section of the pressure recovery curve when considering polymer elasticity is greater than the curve which not considering polymer elasticity. The relaxation time, power-law index, polymer injection concentration mainly affect the radial flow stage of the well testing curve. The relaxation time, power-law index, polymer injection concentration and other polymer flooding parameters mainly affect the radial flow stage of the well testing curve. The larger the polymer flooding parameters, the greater the degree of upwarping of the radial flow derivative curve. This model has important reference significance for well-testing research in polymer flooding oilfields.展开更多
The field test of high concentration polymer flooding has the characteristics of high cost, long cycle and irreversibility of the reservoir development process. In order to ensure the best development effect of the de...The field test of high concentration polymer flooding has the characteristics of high cost, long cycle and irreversibility of the reservoir development process. In order to ensure the best development effect of the development block, this paper simulated and calculated the high concentration polymer flooding development case of the polymer flooding pilot test area through numerical simulation research, and selected the best case through the comparison of various development indicators. The simulation results showed that the larger the polymer dosage and the higher the concentration, the better the oil displacement effect. The best injection method in the construction process was the overall injection of high concentration polymer. The test area should implement high concentration polymer oil displacement as soon as possible. The research results provided theoretical guidance for the future development and management of the pilot area.展开更多
The pilot test of infilling polymer-surfactant-preformed particle gel(PPG)flooding has been successfully implemented after polymer flooding in Ng3 block of Gudao Oilfield in China.However,the production characteristic...The pilot test of infilling polymer-surfactant-preformed particle gel(PPG)flooding has been successfully implemented after polymer flooding in Ng3 block of Gudao Oilfield in China.However,the production characteristics and displacement mechanisms are still unclear,which restricts its further popularization and application.Aiming at this problem,this paper firstly analyzes the production performance of the pilot test and proposed four response types according to the change of water cut curves,including W-type,U-type,V-type response,and no response.Furthermore,the underlying reasons of these four types are analyzed from the aspects of seepage resistance and sweep efficiency.The overall sweep efficiency of gradual-rising W-type,gradual-decreasing W-type,and early V-type response increases from 0.81 to 0.93,0.55 to 0.89,and 0.94 to 1,respectively.And the sum of seepage resistance along the connection line between production well and injection well for U-type and delayed V-type response increases from 0.0994 to 0.2425,and 0.0677 to 0.1654,respectively.Then,the remaining oil distribution after polymer flooding is summarized into four types on the basis of production and geological characteristics,namely disconnected remaining oil,streamline unswept remaining oil,rhythm remaining oil,and interlayer-controlled remaining oil.Furthermore,the main displacement mechanisms for each type are clarified based on the dimensionless seepage resistance and water absorption profile.Generally,improving connectivity by well pattern infilling is the most important for producing disconnected remaining oil.The synergistic effect of well pattern infilling and polymer-surfactant-PPG flooding increases the dimensionless seepage resistance of water channeling regions and forces the subsequent injected water to turn to regions with streamline unswept remaining oil.The improvement of the water absorption profile by polymer-surfactant-PPG flooding and separated layer water injection contributes to displacing rhythm remaining oil and interlayer-controlled remaining oil.Finally,the paper analyzes the relationships between the remaining oil distribution after polymer flooding and production characteristics of infilling polymer-surfactant-PPG flooding.The study helps to deepen the understanding of infilling polymer-surfactant-PPG flooding and has reference significance for more commercial implementations in the future.展开更多
Taking reservoir rocks and fluids of the Daqing,Dagang and Changqing oilfields as research objects,the EOR mechanisms and technical approach of polymer flooding were discussed.By comparing the displacement performance...Taking reservoir rocks and fluids of the Daqing,Dagang and Changqing oilfields as research objects,the EOR mechanisms and technical approach of polymer flooding were discussed.By comparing the displacement performances of ordinary polymer,glycerol,polymer in"sheet-net"structure and heterogeneous weak gel at the same viscosity and concentration,the relationship between the viscosity of polymer displacement agents and displacement performance was demonstrated,and the method of improving polymer flooding effect was worked out.The main mechanism of polymer flooding to increase oil recovery is the swept volume expansion of water injection due to polymer retention in porous media.The viscosity of polymer agents has no positive correlation with polymer flooding effect.Although polymer of"sheet-net"structure has strong capacity in increasing viscosity,it has poor compatibility with pore throat structure of reservoir rock,low injectivity and low shear resistance.Heterogeneous weak gel system has higher adsorption and capture capacity in porous media,which is easy to retain in porous media,and can effectively establish seepage resistance in high permeability layers(zones).Compared with polymer solutions with the same viscosity or concentration,it has stronger ability to expand swept volume.Long term injection of polymer flooding agents will inevitably lead to fluid entry profile reversal,and thus worsening of polymer flooding effect.Alternate injection of high retention and low or non-retention displacement agents can further improve the displacement effect of polymer flooding agents.展开更多
The suggestion that the colloidal-dispersion-gel (CDG) process is superior to normal polymer flooding is misleading and generally incorrect. Colloidal dispersion gels, in their present state of technological developme...The suggestion that the colloidal-dispersion-gel (CDG) process is superior to normal polymer flooding is misleading and generally incorrect. Colloidal dispersion gels, in their present state of technological development, should not be advocated as an improvement to, or substitute for, polymer flooding. Gels made from aluminum-citrate crosslinked polyacrylamides can act as conventional gels and provide effective conformance improvement in treating some types of excess water production problems if sound scientific and engineering principles are respected.展开更多
This study aims to clarify the factors influencing oil recovery of surfactant-polymer(SP)flooding and to establish a quantitative calculation model of oil recovery during different displacement stages from water flood...This study aims to clarify the factors influencing oil recovery of surfactant-polymer(SP)flooding and to establish a quantitative calculation model of oil recovery during different displacement stages from water flooding to SP flooding.The conglomerate reservoir of the Badaowan Formation in the seventh block of the Karamay Oilfield is selected as the research object to reveal the start-up mechanism of residual oil and determine the controlling factors of oil recovery through SP flooding experiments of natural cores and microetching models.The experimental results are used to identify four types of residual oil after water flooding in this conglomerate reservoir with a complex pore structure:oil droplets retained in pore throats by capillary forces,oil cluster trapped at the junction of pores and throats,oil film on the rock surface,isolated oil in dead-ends of flow channel.For the four types of residual oil identified,the SP solution can enhance oil recovery by enlarging the sweep volume and improving the oil displacement efficiency.First,the viscosity-increasing effect of the polymer can effectively reduce the permeability of the displacement liquid phase,change the oil-water mobility ratio,and increase the water absorption.Furthermore,the stronger the shear drag force of the SP solution,the more the crude oil in a porous medium is displaced.Second,the surfactant can change the rock wettability and reduce the absorption capacity of residual oil by lowering interfacial tension.At the same time,the emulsification further increases the viscosity of the SP solution,and the residual oil is recovered effectively under the combined effect of the above two factors.For the four start-up mechanisms of residual oil identified after water flooding,enlarging the sweep volume and improving the oil displacement efficiency are interdependent,but their contribution to enhanced oil recovery are different.The SP flooding system primarily enlarges the sweep volume by increasing viscosity of solution to start two kinds of residual oil such as oil droplet retained in pore throats and isolated oil in dead-ends of flow channel,and primarily improves the oil displacement efficiency by lowing interfacial tension of oil phase to start two kinds of residual oil such as oil cluster trapped at the junction of pores and oil film on the rock surface.On this basis,the experimental results of the oil displacement from seven natural cores show that the pore structure of the reservoir is the main factor influencing water flooding recovery,while the physical properties and original oil saturation have relatively little influence.The main factor influencing SP flooding recovery is the physical and chemical properties of the solution itself,which primarily control the interfacial tension and solution viscosity in the reservoir.The residual oil saturation after water flooding is the material basis of SP flooding,and it is the second-most dominant factor controlling oil recovery.Combined with the analysis results of the influencing factors and reservoir parameters,the water flooding recovery index and SP flooding recovery index are defined to further establish quantitative calculation models of oil recovery under different displacement modes.The average relative errors of the two models are 4.4%and 2.5%,respectively;thus,they can accurately predict the oil recovery of different displacement stages and the ultimate reservoir oil recovery.展开更多
The numerical simulation of polymer flooding is a complex task as this process involves complex physical and chemical reactions,and multiple sets of characteristic parameters are required to properly set the simulatio...The numerical simulation of polymer flooding is a complex task as this process involves complex physical and chemical reactions,and multiple sets of characteristic parameters are required to properly set the simulation.At present,such characteristic parameters are mainly obtained by empirical methods,which typically result in relatively large errors.By analyzing experimentally polymer adsorption,permeability decline,inaccessible pore volume,viscosity-concentration relationship,and rheology,in this study,a conversion equation is provided to convert the experimental data into the parameters needed for the numerical simulation.Some examples are provided to demonstrate the reliability of the proposed approach.展开更多
Polymer has been successfully used to enhance crude oil recovery at high water cut stage.However,the application of polymer flooding is limited by the heterogeneity of reservoir.In this work,the role of polymer floodi...Polymer has been successfully used to enhance crude oil recovery at high water cut stage.However,the application of polymer flooding is limited by the heterogeneity of reservoir.In this work,the role of polymer flooding in heterogeneous reservoir was explored by nuclear magnetic resonance(NMR)spectroscopy.Parallel core displacement experiments were carried out to study polymer flooding in heterogeneous formation.The results showed that the polymer flooding area was related to permeability and pore connectivity.At the end of the water flooding stage,the residual oil was not evenly distributed in porous media.The percent crude oil recovery increased with the increase of pore diameter.Crude oil recovery from cores with larger pores was higher,and water broke through the highly permeable core first.After 0.3 PV polymer injection,the water mobility of the high permeability core decreased.Polymer injection showed a dual effect,an oil displacement effect and a traction effect.The oil displacement effect was responsible for driving out the crude oil in large pores,whereas the traction effect was responsible for driving out residual oil from small pores.After 1 PV polymer injection,the polymer solution channeled through the highly permeable core rapidly.The crude oil in large pores was washed out completely.The NMR water-phase spectrum line of the highly permeable core was much higher than that of the low permeable core.Under different core permeability and porosity,the NMR peak of the crude oil-phase spectrum line indicated that the polymer flooding is mainly effective on pores>40μm.展开更多
The effects of trapping number on enhanced oil recovery by schizophyllan biopolymer flooding in carbonate reservoirs were investigated by running several 1D simulations using measured reservoir rock and fluid data.Sen...The effects of trapping number on enhanced oil recovery by schizophyllan biopolymer flooding in carbonate reservoirs were investigated by running several 1D simulations using measured reservoir rock and fluid data.Sensitivity analysis was performed on different uncertain parameters to history match the oil recovery obtained in the core flooding experiment.These parameters include inaccessible pore volume(IPV),biopolymer adsorption,permeability reduction factor,shear rate coefficient,hardness of injection water,and trapping number.The IPV,biopolymer adsorption,permeability reduction factor,shear rate coefficient and hardness of injection water have negligible effects on oil recovery by biopolymer flooding.Also,history matching of oil recovery data was not possible when these parameters were varied within their typical range of values.When trapping number effect was considered through capillary desaturation curve(CDC),residual oil saturation was reduced from 25.1%without considering its effect or under low trapping number to 10.0%,and the fitting effect for recovery was better.Therefore,we can’t neglect the trapping number effect during biopolymer flooding simulation in the carbonate reservoirs.展开更多
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 oi...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.展开更多
Polymer solutions are used in chemical EOR processes to achieve incremental oil recoveries through obtaining favorable mobility ratios. In the process, the?in-situ?viscosity is a key parameter for the polymer flood de...Polymer solutions are used in chemical EOR processes to achieve incremental oil recoveries through obtaining favorable mobility ratios. In the process, the?in-situ?viscosity is a key parameter for the polymer flood design, as well as the changes in permeability due to the retention or adsorption (e.g.: plugging). Understanding the major causes of the plugging effects allows?predicting injectivity problems as well as optimizing project design. The objective of this work is to use glass-silicon-glass micromodels in combination with tracer particles—attached to the flooded fluids—to qualitatively and quantitatively describe the extent of permeability changes?after polymer injection. Laboratory work is performed in order to determine the physical properties of the polymer solutions when they flow through porous media, such as the presence of permeability reduction/plugging of the micromodel. A statistical analysis of the distribution and extent of plugged areas?is performed and a study of the pressure response during various injection stages will complement the study. A biopolymer (Scleroglucan) was tested and compared to a commonly used polymer, giving a direct insight into their pros and cons. Five different concentrations of polymers were tested and put into relation with their quantitative and qualitative amount of sort of called retention. The amount of adsorption was determined?experimentally in one case in order to draw the significance. By exploiting the potential of GSG-micromodels in combination with tracer particles, it was possible to visualize the reduction of flow paths and its increase during various injections for the first time. Expanding the working principle proposed in this work could provide further understanding of the behavior of any polymers.?The results obtained and workflow presented in this work allow for additional understanding of polymer solutions behavior in flooding applications. Furthermore, the definition of optimized workflows to?assess any kind of solutions in porous media and permeability changes is?supported.展开更多
In order to purify oil recovery wastewater from polymer flooding(ORWPF) in tertiary oil recovery in oil fields, advanced treatment of UV/H2O2/O3 and fine filtration were investigated. The experimental results showed t...In order to purify oil recovery wastewater from polymer flooding(ORWPF) in tertiary oil recovery in oil fields, advanced treatment of UV/H2O2/O3 and fine filtration were investigated. The experimental results showed that polyacrylamide and oil remaining in ORWPF after the conventional treatment process could be effectively removed by UV/H2O2/O3 process. Fine filtration gave a high performance in eliminating suspended solids. The treated ORWPF can meet the quality requirement of the wastewater-bearing polymer injection in oilfield and be safely re-injected into oil reservoirs for oil recovery.展开更多
To understand the displacement characteristics and remaining oil displacement process by the surfactant/polymer(SP) flooding in cores with different pore structures, the effects of pore structure on the enhanced oil r...To understand the displacement characteristics and remaining oil displacement process by the surfactant/polymer(SP) flooding in cores with different pore structures, the effects of pore structure on the enhanced oil recovery of SP flooding was investigated at the pore, core and field scales through conducting experiments on natural core samples with three typical types of pore structures. First, the in-situ nuclear magnetic resonance core flooding test was carried out to capture the remaining oil variation features in the water flooding and SP flooding through these three types of cores. Subsequently, at the core scale, displacement characteristics and performances of water flooding and SP flooding in these three types of cores were evaluated based on the full-size core flooding tests. Finally, at the field scale, production characteristics of SP flooding in the bimodal sandstone reservoir and multimodal conglomerate reservoir were compared using the actual field production data. The results show: as the pore structure gets more and more complex, the water flooding performance gets poorer, but the incremental recovery factor by SP flooding gets higher;the SP flooding can enhance the producing degree of oil in 1-3 μm pores in the unimodal and bimodal core samples, while it produces largely oil in medium and large pores more than 3 μm in pore radius in the multimodal core sample. The core flooding test using full-size core sample demonstrates that the injection of SP solution can significantly raise up the displacement pressure of the multimodal core sample, and greatly enhance recovery factor by emulsifying the remaining oil and enlarging swept volume. Compared with the sandstone reservoir, the multimodal conglomerate reservoir is more prone to channeling. With proper profile control treatments to efficiently enlarge the microscopic and macroscopic swept volumes, SP flooding in the conglomerate reservoir can contribute to lower water cuts and longer effective durations.展开更多
Orthogonal-test-design method has been used to determine the optimal formula by phase behavior and interfacial tension studies, respectively. The effect of each component of two alkaline/surfactant/polymer flooding sy...Orthogonal-test-design method has been used to determine the optimal formula by phase behavior and interfacial tension studies, respectively. The effect of each component of two alkaline/surfactant/polymer flooding systems on interfacial tension is discussed, in which a low-price natural mixed carboxylate (SDC) is used as the major surfactant. The results indicate that the optimal composition is SDC (0.5%), alkaline NaHCO3/Na2CO3 with mass ratio of 1 (1.0%), and hydrolyzed polyacrylamide(0.1%). In the coreflood experiment, their oil recovery is increased by about 25.2% and 26.8% original oil in place, respectively.展开更多
基金This work is supported by the National Natural Science Foundation of China(No.52104049)the Young Elite Scientist Sponsorship Program by Beijing Association for Science and Technology(No.BYESS2023262)Science Foundation of China University of Petroleum,Beijing(No.2462022BJRC004).
文摘Polymer flooding in fractured wells has been extensively applied in oilfields to enhance oil recovery.In contrast to water,polymer solution exhibits non-Newtonian and nonlinear behavior such as effects of shear thinning and shear thickening,polymer convection,diffusion,adsorption retention,inaccessible pore volume and reduced effective permeability.Meanwhile,the flux density and fracture conductivity along the hydraulic fracture are generally non-uniform due to the effects of pressure distribution,formation damage,and proppant breakage.In this paper,we present an oil-water two-phase flow model that captures these complex non-Newtonian and nonlinear behavior,and non-uniform fracture characteristics in fractured polymer flooding.The hydraulic fracture is firstly divided into two parts:high-conductivity fracture near the wellbore and low-conductivity fracture in the far-wellbore section.A hybrid grid system,including perpendicular bisection(PEBI)and Cartesian grid,is applied to discrete the partial differential flow equations,and the local grid refinement method is applied in the near-wellbore region to accurately calculate the pressure distribution and shear rate of polymer solution.The combination of polymer behavior characterizations and numerical flow simulations are applied,resulting in the calculation for the distribution of water saturation,polymer concentration and reservoir pressure.Compared with the polymer flooding well with uniform fracture conductivity,this non-uniform fracture conductivity model exhibits the larger pressure difference,and the shorter bilinear flow period due to the decrease of fracture flow ability in the far-wellbore section.The field case of the fall-off test demonstrates that the proposed method characterizes fracture characteristics more accurately,and yields fracture half-lengths that better match engineering reality,enabling a quantitative segmented characterization of the near-wellbore section with high fracture conductivity and the far-wellbore section with low fracture conductivity.The novelty of this paper is the analysis of pressure performances caused by the fracture dynamics and polymer rheology,as well as an analysis method that derives formation and fracture parameters based on the pressure and its derivative curves.
基金Supported by the National Natural Science Foundation of China(52104049)Science Foundation of China University of Petroleum,Beijing(2462022BJRC004)。
文摘The oil-water two-phase flow pressure-transient analysis model for polymer flooding fractured well is established by considering the comprehensive effects of polymer shear thinning,shear thickening,convection,diffusion,adsorption retention,inaccessible pore volume and effective permeability reduction.The finite volume difference and Newton iteration methods are applied to solve the model,and the effects of fracture conductivity coefficient,injected polymer mass concentration,initial polymer mass concentration and water saturation on the well-test type curves of polymer flooding fractured wells are discussed.The results show that with the increase of fracture conductivity coefficient,the pressure conduction becomes faster and the pressure drop becomes smaller,so the pressure curve of transitional flow goes downward,the duration of bilinear flow becomes shorter,and the linear flow appears earlier and lasts longer.As the injected polymer mass concentration increases,the effective water phase viscosity increases,and the pressure loss increases,so the pressure and pressure derivative curves go upward,and the bilinear flow segment becomes shorter.As the initial polymer mass concentration increases,the effective water phase viscosity increases,so the pressure curve after the wellbore storage segment moves upward as a whole.As the water saturation increases,the relative permeability of water increases,the relative permeability of oil decreases,the total oil-water two-phase mobility becomes larger,and the pressure loss is reduced,so the pressure curve after the wellbore storage segment moves downward as a whole.The reliability and practicability of this new model are verified by the comparison of the results from simplified model and commercial well test software,and the actual well test data.
文摘This review presents our perspective on the factors that have brought polymer flooding to its current state. Insights are provided on why HPAM is the dominant polymer used as well as what is needed to make alternative polymers and mobility-control methods viable. Explanation is given for why large polymer banks are needed for polymer flooding, and design of the injected polymer viscosity is detailed for cases with/without crossflow. The role of fractures and horizontal wells are discussed for improving injectivity and extending polymer flooding to recover oils with viscosities as high as 10,000 cP. Operational improvements are described to minimize mechanical and oxidative stability to allow HPAM polymers to be viable to 70 °C and ATBS polymers to 120 °C. Key factors affecting polymer retention are summarized. The paper points out unresolved issues and future directions for polymer flooding.
文摘At present, the polymer solution is usually assumed to be Newtonian fluid or pseudoplastic fluid, and its elasticity is not considered on the study of polymer flooding well testing model. A large number of experiments have shown that polymer solutions have viscoelasticity, and disregarding the elasticity will cause certain errors in the analysis of polymer solution seepage law. Based on the percolation theory, this paper describes the polymer flooding mechanism from the two aspects of viscous effect and elastic effect, the mathematical model of oil water two-phase three components unsteady flow in viscoelastic polymer flooding was established, and solved by finite difference method, and the well-test curve was drawn to analyze the rule of well test curve in polymer flooding. The results show that, the degree of upward warping in the radial flow section of the pressure recovery curve when considering polymer elasticity is greater than the curve which not considering polymer elasticity. The relaxation time, power-law index, polymer injection concentration mainly affect the radial flow stage of the well testing curve. The relaxation time, power-law index, polymer injection concentration and other polymer flooding parameters mainly affect the radial flow stage of the well testing curve. The larger the polymer flooding parameters, the greater the degree of upwarping of the radial flow derivative curve. This model has important reference significance for well-testing research in polymer flooding oilfields.
文摘The field test of high concentration polymer flooding has the characteristics of high cost, long cycle and irreversibility of the reservoir development process. In order to ensure the best development effect of the development block, this paper simulated and calculated the high concentration polymer flooding development case of the polymer flooding pilot test area through numerical simulation research, and selected the best case through the comparison of various development indicators. The simulation results showed that the larger the polymer dosage and the higher the concentration, the better the oil displacement effect. The best injection method in the construction process was the overall injection of high concentration polymer. The test area should implement high concentration polymer oil displacement as soon as possible. The research results provided theoretical guidance for the future development and management of the pilot area.
基金The authors greatly appreciate the financial support of the National Natural Science Foundation of China(Grant No.52104027)the Project supported by the Joint Funds of the National Natural Science Foundation of China(Grant No.U21B2070)the Shandong Provincial Natural Science Foundation(Grant No.ZR2021ME072).
文摘The pilot test of infilling polymer-surfactant-preformed particle gel(PPG)flooding has been successfully implemented after polymer flooding in Ng3 block of Gudao Oilfield in China.However,the production characteristics and displacement mechanisms are still unclear,which restricts its further popularization and application.Aiming at this problem,this paper firstly analyzes the production performance of the pilot test and proposed four response types according to the change of water cut curves,including W-type,U-type,V-type response,and no response.Furthermore,the underlying reasons of these four types are analyzed from the aspects of seepage resistance and sweep efficiency.The overall sweep efficiency of gradual-rising W-type,gradual-decreasing W-type,and early V-type response increases from 0.81 to 0.93,0.55 to 0.89,and 0.94 to 1,respectively.And the sum of seepage resistance along the connection line between production well and injection well for U-type and delayed V-type response increases from 0.0994 to 0.2425,and 0.0677 to 0.1654,respectively.Then,the remaining oil distribution after polymer flooding is summarized into four types on the basis of production and geological characteristics,namely disconnected remaining oil,streamline unswept remaining oil,rhythm remaining oil,and interlayer-controlled remaining oil.Furthermore,the main displacement mechanisms for each type are clarified based on the dimensionless seepage resistance and water absorption profile.Generally,improving connectivity by well pattern infilling is the most important for producing disconnected remaining oil.The synergistic effect of well pattern infilling and polymer-surfactant-PPG flooding increases the dimensionless seepage resistance of water channeling regions and forces the subsequent injected water to turn to regions with streamline unswept remaining oil.The improvement of the water absorption profile by polymer-surfactant-PPG flooding and separated layer water injection contributes to displacing rhythm remaining oil and interlayer-controlled remaining oil.Finally,the paper analyzes the relationships between the remaining oil distribution after polymer flooding and production characteristics of infilling polymer-surfactant-PPG flooding.The study helps to deepen the understanding of infilling polymer-surfactant-PPG flooding and has reference significance for more commercial implementations in the future.
基金Supported by the National Major Special Project of Oil and Gas During the 13th Five-Year Plan Period(NO.2016ZX05058-003-010)General Program of National Natural Science Foundation of China(NO.51574086)Postdoctoral Innovative Talent Support Program of China(NO.BX20190065)。
文摘Taking reservoir rocks and fluids of the Daqing,Dagang and Changqing oilfields as research objects,the EOR mechanisms and technical approach of polymer flooding were discussed.By comparing the displacement performances of ordinary polymer,glycerol,polymer in"sheet-net"structure and heterogeneous weak gel at the same viscosity and concentration,the relationship between the viscosity of polymer displacement agents and displacement performance was demonstrated,and the method of improving polymer flooding effect was worked out.The main mechanism of polymer flooding to increase oil recovery is the swept volume expansion of water injection due to polymer retention in porous media.The viscosity of polymer agents has no positive correlation with polymer flooding effect.Although polymer of"sheet-net"structure has strong capacity in increasing viscosity,it has poor compatibility with pore throat structure of reservoir rock,low injectivity and low shear resistance.Heterogeneous weak gel system has higher adsorption and capture capacity in porous media,which is easy to retain in porous media,and can effectively establish seepage resistance in high permeability layers(zones).Compared with polymer solutions with the same viscosity or concentration,it has stronger ability to expand swept volume.Long term injection of polymer flooding agents will inevitably lead to fluid entry profile reversal,and thus worsening of polymer flooding effect.Alternate injection of high retention and low or non-retention displacement agents can further improve the displacement effect of polymer flooding agents.
文摘The suggestion that the colloidal-dispersion-gel (CDG) process is superior to normal polymer flooding is misleading and generally incorrect. Colloidal dispersion gels, in their present state of technological development, should not be advocated as an improvement to, or substitute for, polymer flooding. Gels made from aluminum-citrate crosslinked polyacrylamides can act as conventional gels and provide effective conformance improvement in treating some types of excess water production problems if sound scientific and engineering principles are respected.
基金supported by the National Natural Science Foundation of China(No.41902141)the Fundamental Research Fund for the Central Universities(No.E1E40403)the PetroChina Innovation Foundation(No.2018D-5007-0103)
文摘This study aims to clarify the factors influencing oil recovery of surfactant-polymer(SP)flooding and to establish a quantitative calculation model of oil recovery during different displacement stages from water flooding to SP flooding.The conglomerate reservoir of the Badaowan Formation in the seventh block of the Karamay Oilfield is selected as the research object to reveal the start-up mechanism of residual oil and determine the controlling factors of oil recovery through SP flooding experiments of natural cores and microetching models.The experimental results are used to identify four types of residual oil after water flooding in this conglomerate reservoir with a complex pore structure:oil droplets retained in pore throats by capillary forces,oil cluster trapped at the junction of pores and throats,oil film on the rock surface,isolated oil in dead-ends of flow channel.For the four types of residual oil identified,the SP solution can enhance oil recovery by enlarging the sweep volume and improving the oil displacement efficiency.First,the viscosity-increasing effect of the polymer can effectively reduce the permeability of the displacement liquid phase,change the oil-water mobility ratio,and increase the water absorption.Furthermore,the stronger the shear drag force of the SP solution,the more the crude oil in a porous medium is displaced.Second,the surfactant can change the rock wettability and reduce the absorption capacity of residual oil by lowering interfacial tension.At the same time,the emulsification further increases the viscosity of the SP solution,and the residual oil is recovered effectively under the combined effect of the above two factors.For the four start-up mechanisms of residual oil identified after water flooding,enlarging the sweep volume and improving the oil displacement efficiency are interdependent,but their contribution to enhanced oil recovery are different.The SP flooding system primarily enlarges the sweep volume by increasing viscosity of solution to start two kinds of residual oil such as oil droplet retained in pore throats and isolated oil in dead-ends of flow channel,and primarily improves the oil displacement efficiency by lowing interfacial tension of oil phase to start two kinds of residual oil such as oil cluster trapped at the junction of pores and oil film on the rock surface.On this basis,the experimental results of the oil displacement from seven natural cores show that the pore structure of the reservoir is the main factor influencing water flooding recovery,while the physical properties and original oil saturation have relatively little influence.The main factor influencing SP flooding recovery is the physical and chemical properties of the solution itself,which primarily control the interfacial tension and solution viscosity in the reservoir.The residual oil saturation after water flooding is the material basis of SP flooding,and it is the second-most dominant factor controlling oil recovery.Combined with the analysis results of the influencing factors and reservoir parameters,the water flooding recovery index and SP flooding recovery index are defined to further establish quantitative calculation models of oil recovery under different displacement modes.The average relative errors of the two models are 4.4%and 2.5%,respectively;thus,they can accurately predict the oil recovery of different displacement stages and the ultimate reservoir oil recovery.
基金supported by Hubei Provincial Natural Science Foundation of China(Grant No.2020CFB377)the National Natural Science Foundation of China(Grant No.52104020).
文摘The numerical simulation of polymer flooding is a complex task as this process involves complex physical and chemical reactions,and multiple sets of characteristic parameters are required to properly set the simulation.At present,such characteristic parameters are mainly obtained by empirical methods,which typically result in relatively large errors.By analyzing experimentally polymer adsorption,permeability decline,inaccessible pore volume,viscosity-concentration relationship,and rheology,in this study,a conversion equation is provided to convert the experimental data into the parameters needed for the numerical simulation.Some examples are provided to demonstrate the reliability of the proposed approach.
文摘Polymer has been successfully used to enhance crude oil recovery at high water cut stage.However,the application of polymer flooding is limited by the heterogeneity of reservoir.In this work,the role of polymer flooding in heterogeneous reservoir was explored by nuclear magnetic resonance(NMR)spectroscopy.Parallel core displacement experiments were carried out to study polymer flooding in heterogeneous formation.The results showed that the polymer flooding area was related to permeability and pore connectivity.At the end of the water flooding stage,the residual oil was not evenly distributed in porous media.The percent crude oil recovery increased with the increase of pore diameter.Crude oil recovery from cores with larger pores was higher,and water broke through the highly permeable core first.After 0.3 PV polymer injection,the water mobility of the high permeability core decreased.Polymer injection showed a dual effect,an oil displacement effect and a traction effect.The oil displacement effect was responsible for driving out the crude oil in large pores,whereas the traction effect was responsible for driving out residual oil from small pores.After 1 PV polymer injection,the polymer solution channeled through the highly permeable core rapidly.The crude oil in large pores was washed out completely.The NMR water-phase spectrum line of the highly permeable core was much higher than that of the low permeable core.Under different core permeability and porosity,the NMR peak of the crude oil-phase spectrum line indicated that the polymer flooding is mainly effective on pores>40μm.
基金Khalifa University of Science and Technology for funding this research under Award No. [FSU-2018-26]
文摘The effects of trapping number on enhanced oil recovery by schizophyllan biopolymer flooding in carbonate reservoirs were investigated by running several 1D simulations using measured reservoir rock and fluid data.Sensitivity analysis was performed on different uncertain parameters to history match the oil recovery obtained in the core flooding experiment.These parameters include inaccessible pore volume(IPV),biopolymer adsorption,permeability reduction factor,shear rate coefficient,hardness of injection water,and trapping number.The IPV,biopolymer adsorption,permeability reduction factor,shear rate coefficient and hardness of injection water have negligible effects on oil recovery by biopolymer flooding.Also,history matching of oil recovery data was not possible when these parameters were varied within their typical range of values.When trapping number effect was considered through capillary desaturation curve(CDC),residual oil saturation was reduced from 25.1%without considering its effect or under low trapping number to 10.0%,and the fitting effect for recovery was better.Therefore,we can’t neglect the trapping number effect during biopolymer flooding simulation in the carbonate reservoirs.
基金supported by the National High Technology Research and Development Program of China (863 Program: 2006AA09Z315 and 2007AA090701-3)
文摘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.
文摘Polymer solutions are used in chemical EOR processes to achieve incremental oil recoveries through obtaining favorable mobility ratios. In the process, the?in-situ?viscosity is a key parameter for the polymer flood design, as well as the changes in permeability due to the retention or adsorption (e.g.: plugging). Understanding the major causes of the plugging effects allows?predicting injectivity problems as well as optimizing project design. The objective of this work is to use glass-silicon-glass micromodels in combination with tracer particles—attached to the flooded fluids—to qualitatively and quantitatively describe the extent of permeability changes?after polymer injection. Laboratory work is performed in order to determine the physical properties of the polymer solutions when they flow through porous media, such as the presence of permeability reduction/plugging of the micromodel. A statistical analysis of the distribution and extent of plugged areas?is performed and a study of the pressure response during various injection stages will complement the study. A biopolymer (Scleroglucan) was tested and compared to a commonly used polymer, giving a direct insight into their pros and cons. Five different concentrations of polymers were tested and put into relation with their quantitative and qualitative amount of sort of called retention. The amount of adsorption was determined?experimentally in one case in order to draw the significance. By exploiting the potential of GSG-micromodels in combination with tracer particles, it was possible to visualize the reduction of flow paths and its increase during various injections for the first time. Expanding the working principle proposed in this work could provide further understanding of the behavior of any polymers.?The results obtained and workflow presented in this work allow for additional understanding of polymer solutions behavior in flooding applications. Furthermore, the definition of optimized workflows to?assess any kind of solutions in porous media and permeability changes is?supported.
文摘In order to purify oil recovery wastewater from polymer flooding(ORWPF) in tertiary oil recovery in oil fields, advanced treatment of UV/H2O2/O3 and fine filtration were investigated. The experimental results showed that polyacrylamide and oil remaining in ORWPF after the conventional treatment process could be effectively removed by UV/H2O2/O3 process. Fine filtration gave a high performance in eliminating suspended solids. The treated ORWPF can meet the quality requirement of the wastewater-bearing polymer injection in oilfield and be safely re-injected into oil reservoirs for oil recovery.
基金Supported by China National Science and Technology Major Project(2016ZX05025-003-010) and (2016ZX05010-005).
文摘To understand the displacement characteristics and remaining oil displacement process by the surfactant/polymer(SP) flooding in cores with different pore structures, the effects of pore structure on the enhanced oil recovery of SP flooding was investigated at the pore, core and field scales through conducting experiments on natural core samples with three typical types of pore structures. First, the in-situ nuclear magnetic resonance core flooding test was carried out to capture the remaining oil variation features in the water flooding and SP flooding through these three types of cores. Subsequently, at the core scale, displacement characteristics and performances of water flooding and SP flooding in these three types of cores were evaluated based on the full-size core flooding tests. Finally, at the field scale, production characteristics of SP flooding in the bimodal sandstone reservoir and multimodal conglomerate reservoir were compared using the actual field production data. The results show: as the pore structure gets more and more complex, the water flooding performance gets poorer, but the incremental recovery factor by SP flooding gets higher;the SP flooding can enhance the producing degree of oil in 1-3 μm pores in the unimodal and bimodal core samples, while it produces largely oil in medium and large pores more than 3 μm in pore radius in the multimodal core sample. The core flooding test using full-size core sample demonstrates that the injection of SP solution can significantly raise up the displacement pressure of the multimodal core sample, and greatly enhance recovery factor by emulsifying the remaining oil and enlarging swept volume. Compared with the sandstone reservoir, the multimodal conglomerate reservoir is more prone to channeling. With proper profile control treatments to efficiently enlarge the microscopic and macroscopic swept volumes, SP flooding in the conglomerate reservoir can contribute to lower water cuts and longer effective durations.
文摘Orthogonal-test-design method has been used to determine the optimal formula by phase behavior and interfacial tension studies, respectively. The effect of each component of two alkaline/surfactant/polymer flooding systems on interfacial tension is discussed, in which a low-price natural mixed carboxylate (SDC) is used as the major surfactant. The results indicate that the optimal composition is SDC (0.5%), alkaline NaHCO3/Na2CO3 with mass ratio of 1 (1.0%), and hydrolyzed polyacrylamide(0.1%). In the coreflood experiment, their oil recovery is increased by about 25.2% and 26.8% original oil in place, respectively.
