Polymer Flooding Process Research Articles

Using surface modified clay nanoparticles to improve rheological behavior of Hydrolized Polyacrylamid (HPAM) solution for enhanced oil recovery with polymer flooding

In this communication, effect of Surface Modified Clay Nanoparticles (SMCN) on rheological behavior of Hydrolized Polyacrylamid (HPAM) solution and also its resistance against the increases in temperature and salinity were investigated experimentally. An increases in polymer solution viscosity result in a decrease in mobility ratio then consequently it may increase the polymer flooding efficiency. High pressures imposed on polymers during flooding processes cause a considerable shear stress on them, which lead to breakage of polymer chains. In addition, at elevated temperatures, certain chemical reactions are accelerated and subsequently this force polymer chains to compress. This kind of behavior (compactness of polymer chains) can be observed in a saline environment. Therefore, polymer viscosity and consequent flooding process efficiency is decreased. To prevent deformation of polymers and increase the internal friction of the solution, surface of certain clay nanoparticles were modified by specific tetrahedral redundants and located between polymer chains.Finally, the potential utilization of these novel clay nanoparticles in improving the performance of polymer flooding on an unconsolidated sandpacks were investigated. According to the results, we suggest 0.1% wt concentration of SMCN as the optimum concentration in which the SMCN-HPAM solution is stable. In addition, results indicate that adding SMCN improves the resistance of polymer solution against an increases in salinity and temperature, and also its shear thinning behavior. Moreover, the experimental result indicates that SMCN-HPAM increases the oil recovery about 33% more than ordinary polymer flooding processes.

Применение полимерного заводнения для увеличения коэффициента извлечения нефти

Применение полимерного заводнения для увеличения коэффициента извлечения нефти

Rheological behavior of hydrolyzed polyacrylamide solution flowing through a molecular weight adjusting device with porous medium

The separate-layer injection in different interlayers and the injection of the same-molecular-weight polymer solution in a layer are necessary in the polymer flooding process because of heterogeneous multilayer sandstone reservoirs in EOR projects. To alleviate the matching problems between the layer permeability and the injected polymer molecular weight, a molecular weight adjusting device with porous medium was designed on the basis of mechanical degradation principle. In terms of four variables (polymer concentration, pore diameter, length of shear component and flow rate), the rheological behavior of hydrolyzed polyacrylamide (HPAM) solution flowing through the device was investigated in detail. The change of these variables is able to control the shear rate of HPAM solutions through ceramic foam, and achieve the desired degree of shear degradation and the final rheological parameters—viscosity loss, viscoelasticity and pressure drop. Therefore, a linear relationship between viscosity loss and shearing rate was established so as to obtain the targeted viscosity easily. Field tests in the Daqing Oil Field showed that the polymer molecular weight could drop 20% to 50%. In a word, the results could guide the industrial application of the novel device and the further study of polymer degradation flowing through the porous medium.

Rheological Modeling and Numerical Simulation of HPAM Polymer Viscosity in Porous Media

Polymer flooding is a commercially proven approach for enhanced oil recovery from mature oil fields. The fundamental mechanism of polymer flooding for improving oil recovery is to increase the viscosity of displacing fluid, thereby creating a favorable mobility ratio for improved volumetric sweep efficiency. Therefore, development of an adequate model for prediction of polymer viscosity is the successful key of this process. This article presents a comprehensive investigation of hydrolyzed polyacrylamide viscosity for a wider and better understanding of the polymer flooding process. A fundamental mathematic model of polymer viscosity in porous media is described and a series of numerical simulations have been done to determine the dependence of polymer viscosity on polymer solution properties and reservoir conditions. The simulation results indicate that pH, salinity, polymer concentration, molecular weight, and alkaline are the main parameters that strongly influence the viscosity of hydrolyzed polyacrylamide. With an appropriate control of these factors, the efficiency of chemical flooding will be significantly improved in both economic and technical aspects.

Unsteady Convective Heat Transfer of Power-Law Fluid with Variable Fluid Properties in a Concentric Annulus Originating from a Polymer Flooding Process

We study the unsteady convective heat transfer of power-law fluid with variable fluid properties in a concentric annulus with isothermal surface. The problem is originated from the polymer flooding process between a sucker rod and oil well. A new power-law rheological model is proposed, which takes the effects of temperature on fluid viscosity and thermal conductivity into account. Numerical solutions are presented for velocity and temperature fields using the Chebyshev spectral method coupled with the strong stability-preserving Runge–Kutta time discretization. The exponential convergence is verified by accuracy testing between a smooth exact solution of the Partial Differential Equations (PDEs) with source terms and the numerical approximation of manufactured solutions. It is found that heat transfer is enhanced in the variable power-law index model, and a decrease in power-law index of pseudoplastic fluids promotes heat transfer due to the increased Nusselt number. Moreover, the influences of other parameters on convective heat transfer behaviors are discussed in detail.

Response Surface Design for Estimating the Optimal Operating Conditions in the Polymer Flooding Process

The objective of this study is to apply experimental design for sensitivity investigation and determination of the optimum condition of operating variables in enhanced oil recovery by polymer flooding. These experiments were designed consisting of 14 cases by the D-optimal design. The maximum net present value is obtained at $244.94 mm, in which an optimum operating variable is injected at a polymer concentration of 1,780 ppm and slug size of 2.6 mlb under reservoir conditions. This study successfully applied optimal operating parameters in a polymer flood, which is an economical way of obtaining the maximum profit in a short period of time and with the fewest number of experiments.

Enhanced Oil Recovery Using Polymer/nanosilica

Recent developments in nanotechnology illustrates that addition of nanoparticles in the polymer flooding process can improve the oil recovery factor. But there exists few researches about the polymer performance in the presence of nanoparticles. Also there is no information about the effect of silica nanoparticles on the heavy oil recovery during the polymer flooding by anionic hydrolyzed polyacrylamide (HPAM). Therefore, for the first time in this study the effect of nanosilica (NS) in the polymer flooding in the presence of salt on the oil recovery factor has been investigated in a strongly oil wet five-spot glass micromodel saturated with the heavy oil and the image processing technique was applied to analyze the displacement mechanisms and also for calculation of the efficiency in each flooding test. The oil recovery factor after one pore volume of the injected fluid has been obtained and results indicate that in the presence of NS an improvement about 10% in the ultimate oil recovery can be achieved and this is due to the viscosity enhancement of the injected fluid. Also it has been understood that nanoparticles have ability to change the wettability to water-wet in some portions of the micromodel.

Analysis of Capillary–Viscous–Gravity Forces in Biopolymer Flooding with a Sensitivity Analysis on Polymer and Porous Medium Parameters

Gravity, viscous, and capillary are three main forces affecting flow characteristics in porous media. No analytical solution can be found to model the flow by considering all these forces. In this work, by considering all these forces, the polymer-flooding process is modeled by using a numerical simulation approach. For characterizing the polymer, the modified Blake–Kozeny model is chosen, which benefits consideration of the permeability reduction due to polymer adsorption on the rock surface.

Research on oil displacement mechanism in conglomerate using CT scanning method

Taking the conglomerate from Xinjiang Oilfield as study object, the porosity distribution characteristics of the conglomerate were analyzed with CT scanning; through the online monitoring of the water and polymer flooding process in a conglomerate core using an CT scanning system, the saturation profile along the core and the CT reconstructed images of core section during the displacing process were obtained; oil displacement mechanism was analyzed according to a new characterization parameter, “oil saturation frequency distribution”. The results show that the conglomerate has strong heterogeneity, resulting in “dominant channels”, and in turn ineffective water circulation and low water flooding oil recovery, moreover, the oil in high oil saturation area is produced first. In polymer flooding, the oil in high and medium oil saturation areas can be produced but the oil in low oil saturation areas still cannot be produced. Oil produced in the subsequent water flooding is still mainly from the high oil saturation areas. For conglomerate reservoirs, previous water flooding should reach as high water cut as possible so as to strengthen the slug effect of the polymer. Meanwhile the injection volume of polymer should be reduced, and a subsequent water flooding should be used to push the polymer slug to produce oil.

Experimental Investigation of Flooding Hydrolyzed–Sulfonated Polymers for EOR Process in a Carbonate Reservoir

The main purposes of this study were to scrutinize experimentally effects of polymer and rock types on the oil recovery using water and polymer flooding processes. Four dynamic flooding experiments were carried out at simulated reservoir condition of temperature and pressure. According to the obtained results, the ultimate oil recovery by water flooding in highly fractured reservoirs was less than reservoirs with the microfractures. The results of polymer flooding showed that in addition the polymer molecular weight, the sulfonation of polymers also affects the oil recovery.

Water Saturation Model Optimization after Polymer Flooding

In this paper, the conducting model which is more suitable to describe the reservoir in the process of polymer flooding was selected, according to the reservoir properties. Based on the polymer solution conductance laws and the polymer flooding rock resistivity experiments, by injecting various types of polymers and water with different salinities, the rock resistivity change rule was studied. The change rule of the Archie model parameters in the polymer flooding process was analyzed and the accuracy of the dual water model was analyzed by means of the Litho-electric experiment data. On the basis of rock physical property analysis data, combined with the actual logging rules, the parameters interpretation model of porosity, permeability, irreducible water saturation and shale content were established. Using the core analyze data to contrast the practical application effect of the interpretation model, the result show that, the conclusion of the model corresponds to reality.

A Study of Properties of Dilute Polymer Systems Prepared with Polymer-Bearing Wastewater

Isoconcentration flooding systems were prepared, their viscosity, shearing resistance, viscoelasticity, stability and molecule clew size were measured and the impact of polymer-bearing wastewater on polymer performance was determined in order to study the impact of polymer systems prepared with polymer-bearing wastewater on polymer performance in the polymer flooding process of Daqing oilfield. The result indicates: at the same preparation concentration, the storage modulus, loss modulus, viscosity stability, molecule clew size and shearing resistance of polymer solution systems are increased with increase in the polymer concentration in wastewater, the properties of a fresh water system are better than those of a wastewater system, the properties of a physicochemical wastewater system are better than those of a biochemical wastewater system, and the residual polymers in sewage have good viscosity increasing capacity. Therefore, polymer-bearing wastewater improves the properties of polymer systems to a certain degree and can be used as water for polymer system preparation.

The Effects of the Shear-thinning Property of Injection Fluid on the Performance of Polymer Flood

Assessment of the potential of a polymer flood process for mobility control requires an accurate model on the viscosities of displacement fluids. Because most polymers used in enhanced oil recovery exhibit shear-thinning behavior, effective viscosity of polymer solution is a highly nonlinear function of shear rate. A reservoir simulator, including the model for the shear-rate dependence of viscosity, was used to investigate the shear-thinning effects of polymer solution on the performance of the reservoir in a five-spot pattern operating under polymer flood followed by waterflood. The model can be used as a quantitative tool to evaluate the comparative studies of different polymer flooding scenarios with respect to shear-rate dependence of fluids' viscosities. Results of cumulative oil recovery, injectivity, and distributions of polymer concentration and aqueous phase viscosity are presented for parameters of shear-rate dependencies, permeability, and injection rate. The results of this work have proven the importance of taking non-Newtonian behavior of polymer solution into account for the successful evaluation of polymer flood processes. Simulations carried in a 3D model suggest that the shear-thinning property improves injectivity considerably because the shear rate encountered near the injection well alters the viscosity of displacing fluid. However, it makes almost negligible differences in oil recovery because a significant increase in viscosity was developed at the fluid front in the reservoir. A thorough understanding of polymer rheology in the reservoir and accurate numerical modeling are of fundamental importance for the exact estimation on the performance of polymer flood.

Performance of Polymer Flooding in Anisotropic Reservoirs with Discontinuous Streaks of Shale

Many oil reservoirs contain discontinuous shale streaks, which may affect the flow behavior as well as oil recovery efficiency. To investigate and compare the performances of polymer flood processes in anisotropic shaly reservoirs, an extensive numerical simulation was performed for polymer flood followed by waterflood. A series of polymer and water injection simulations have been carried out at various conditions in the length, direction, and spacing of shale streaks and level of reservoir anisotropy. Reservoir performances were compared in terms of cumulative recovery and water-oil ratio at the production well and injectivity at the injection well. Results from the study have demonstrated that oil recovery can be significantly affected by shale streaks with increased length and shorter space. It was observed that the shale streaks cause bypassing of displacing fluids due to disruption of main flow path and, consequently, lower injectivity. Increasing shale content causes the degree of fingering to be increased significantly during polymer flooding. The effects of heterogeneity introduced by streaks of shale were maximized when the direction of displacing fluid flow was perpendicular to the direction of shale streaks and parallel to higher permeability in the anisotropic reservoir models. Results of this work can be helpful for successful design and accurate prediction of EOR processes based on shale distribution in anisotropic reservoirs.

Improvement of Polymer Flooding Using in-Situ Releasing of Smart Nano-Scale Coated Polymer Particles in Porous Media

The main purpose of this paper is modeling and simulation of in-situ releasing of smart nano-sized core-shell particles at the water-oil interface during polymer flooding. During the polymer flooding process, when these nano-particles reach the water-oil interface, migrate to the oil phase and the hydrophobic layer of them dissolves in this phase. After dissolution of this protective nano-sized layer, the hydrophilic core containing a water-soluble ultra high molecular weight polymer diffuses back into the water phase and with dissolving in this phase, dramatically increases viscosity of flooding water in the neighborhood of the water-oil interface. In this study, two different time-dependent dissolution models are implemented. A swellable-chain disentanglement model with concentration-dependent diffusion coefficient is considered for dissolution of the core polymer into the aqueous phase, whereas, surface chain disentanglement with constant diffusion coefficient is considered for dissolution of the shell polymer in the oil phase. Using finite difference scheme, the governing equations are numerically solved by defining some dimensionless parameters for the main parameters as well as the moving boundaries. In addition, some experimental flooding tests in micromodel were carried out to experimentally investigate the recovery factor of using these particles compared to those of the conventional polymer flooding.

Application of ceramic membranes in the treatment of oilfield-produced water: Effects of polyacrylamide and inorganic salts

Polyacrylamide has been widely used for polymer flooding in oil production. Wastewater is produced in the polymer flooding process. In this work, a ceramic membrane system was used to treat the wastewater. The effects of membrane pore size and PAM concentrations on the filtration performance were investigated. With the increase of the membrane pore size, the flux declined severely. When the PAM concentration was lower than the critical micelle concentration (CMC), the pseudo-steady flux decreased with the PAM concentration. When the PAM concentration was close to or higher than the CMC, the PAM concentration had little influence on the PSF. For the ultrafiltration membranes, the average MW of PAM in the permeate changed little with different PAM concentrations. However, for the microfiltration membranes, the average MW of PAM in the permeate decreased with the PAM concentration. The effect of NaCl concentration on the filtration of PAM solutions was studied. As the NaCl concentration increased, the change of PAM morphology caused the PSF to decrease significantly. Membrane fouling mechanisms and membrane cleaning methods were also discussed. Pore blocking and gel layer formation both contributed to the flux decline. The fouled membrane was easily cleaned by a NaOH aqueous solution with pH>12.

Adjoint-based Optimization of Polymer Flooding Process with Free Terminal Time

Adjoint-based Optimization of Polymer Flooding Process with Free Terminal Time

The Application of Horizontal and Vertical Well Patterns During Polymer Flood Processes in Anisotropic Reservoirs

Using horizontal wells in a polymer flood process, higher sweep efficiency is expected compared with the use of conventional patterns by vertical wells. However, the use of horizontal wells is very sensitive to the well pattern designed to operate the process. This article presents an analysis of how the overall performance of a polymer flood process is influenced by the well pattern using a horizontal injector and producer in different configurations. A three-dimensional numerical model for fluid flow and mass transport is used to analyze the performance of the reservoir. The potential for a horizontal well application was assessed through different scenarios in combinations of injection and production wells and reservoir anisotropy. Results from the study have demonstrated that a significant amount of additional oil can be recovered and injectivity was remarkably improved by utilizing a combination of horizontal wells. The improvement of injectivity through a horizontal injection well was higher when it was combined with a horizontal producer parallel to the injector. The overall performances in anisotropic reservoirs strongly depend on the type of wells considered and the orientation of the horizontal wells with respect to the permeability directions. A combination of horizontal wells placed parallel to the low permeability direction yields the best performance.

Improving Performances of Hydrophobically Modified Polyacrylamide in Mineralized Water by Block Polyether with Branched Structure

The hydrophobically modified polyacrylamide (HMPAM) has been received considerable attention in enhanced oil recovery (EOR) processes. The effect of a block polyether with branched structure polyoxyethylene-polyoxypropylene-polyethylene-polyamine (expressed as polyether or PEO-PPO-PEA) on the rheological performances of HMPAM solutions with 8074 mg · L−1 total salinity were investigated at various time and 65°C in order to satisfy the needs of EOR in high temperature and salinity reservoirs. Results reveal that the addition of a certain amount of PEO-PPO-PEA can improve the viscosity and viscoelasticity of HMPAM solution in mineralized water because of the formation of a strong net-like structure. From the results of the flow characteristic measurement and the core flooding test, it can be concluded that the 1750 mg · L−1 HMPAM system with 25 mg · L−1 PEO-PPO-PEA is applicable to use as a displacement system in polymer flooding process at 65°C and 8074 mg · L−1 total salinity.

Dynamic Optimization of a Polymer Flooding Process Based on Implicit Discrete Maximum Principle

Polymer flooding is one of the most important technologies for enhanced oil recovery (EOR). In this paper, an optimal control model of distributed parameter systems (DPSs) for polymer injection strategies is established, which involves the performance index as maximum of the profit, the governing equations as the fluid flow equations of polymer flooding, and some inequality constraints as polymer concentration and injection amount limitation. The optimal control model is discretized by full implicit finite‐difference method. To cope with the discrete optimal control problem (OCP), the necessary conditions for optimality are obtained through application of the calculus of variations and Pontryagin’s discrete maximum principle. A modified gradient method with new adjoint construction is proposed for the computation of optimal injection strategies. The numerical results of an example illustrate the effectiveness of the proposed method.