Polymers In Porous Media Research Articles

Research on Variation Law and Prediction Model of Working Viscosity of Salt Resistant Polymer

Using seepage experiments and theoretical methods, the effects of injection fluid viscosity and injection speed on the change of working viscosity of salt-resistant polymers in porous media with different permeability are studied. And developed a working viscosity prediction model. The results show that as the permeability and viscosity of the injection fluid increase, the working viscosity of the salt-resistant polymer in the porous medium increases; as the injection speed increases, the polymer exhibits viscoelasticity, and the working viscosity decreases first and then increases; under the same conditions, the working viscosity of the salt-resistant polymer is higher than that of the ordinary polymer; in the gray correlation analysis, the correlation coefficient of the injection fluid viscosity and working viscosity is 0.958, the permeability is 0.954, and the injection speed is 0.709; a multivariate statistical regression method is used to give a prediction model for the working viscosity of salt-resistant polymers. The average deviation between the predicted value and the actual calculated value is only 4.40%.

Injection of water slug containing two polymers in porous media: Analytical solution for two-phase flow accounting for adsorption effects

Polymer flooding is the most applied chemical method of enhanced oil recovery (EOR). Usually this process consists of injecting a slug containing dissolved chemicals displaced by water. This technique is modeled by a system of conservation laws with constant initial condition and not constant boundary conditions. In this paper we extend the two solute one-dimensional chromatography problem solution (Rhee et al., 2001) for a two-phase environment. The exact solution for the injection of a slug containing two dissolved polymers driven by water in an oil reservoir is developed. It is considered that both polymers may adsorb in porous media following Langmuir's adsorption isotherm. The solution is built splitting the original system into a purely chromatographic problem (auxiliary system), and a lifting equation that considers the hydrodynamics properties of the system. Due to the chase water drive, interactions between waves arise along the space-time plane and change the path of the characteristics at the rear of the slug. The presented solution is composed by rarefaction and shock waves, and constant states. Moreover, a complete chromatography cycle develops in the porous media (complete separation of the chemical components).

Laboratory treatment of HPAM polymers for injection in low permeability carbonate reservoirs

Polymeric solutions are injected into petroleum reservoirs to improve sweep efficiency of enhanced oil recovery processes. Viscous polymeric solutions cannot be injected into non-fractured low permeability carbonates (k < 50 mD) if a significant fraction of pore throats is smaller than the polymer molecules. Mechanical shear degradation and aggressive microfiltration can be applied as tools to modify the molecular weight distribution (or hydrodynamic radius) of polymers. High speed mechanical shearing in a laboratory blender showed significant reduction in viscosity and polydispersity for the polymer stock solutions with improvement in filterability and transport in low permeability porous media. Aggressive filtration through small sized filter papers proved to be a good technique for refinement of molecular weight distribution and removing larger molecules for successful injection in low permeability carbonates. Dynamic light scattering (DLS) method was used to measure the size distribution of shear degraded polymer solutions at low concentrations. The optimum shear degradation required for a high MW polymer to be successfully injected into a low permeability carbonate reservoir was decided by comparing the polymer size distribution with the pore throat diameter distribution obtained from mercury injection capillary pressure (MICP) for the rock. This novel technique was successfully applied for injection of viscous polymer solutions in carbonates with permeability less than 20 mD. The pore throat distribution of a porous medium is more important than the permeability (or average hydraulic radius) for the transport of polymers in porous media.

Progress Report on Phase Separation in Polymer Solutions.

Polymeric porous media (PPM) are widely used as advanced materials, such as sound dampening foams, lithium-ion batteries, stretchable sensors, and biofilters. The functionality, reliability, and durability of these materials have a strong dependence on the microstructural patterns of PPM. One underlying mechanism for the formation of porosity in PPM is phase separation, which engenders polymer-rich and polymer-poor (pore) phases. Herein, the phase separation in polymer solutions is discussed from two different aspects: diffusion and hydrodynamic effects. For phase separation governed by diffusion, two novel morphological transitions are reviewed: "cluster-to-percolation" and "percolation-to-droplets," which are attributed to an effect that the polymer-rich and the solvent-rich phases reach the equilibrium states asynchronously. In the case dictated by hydrodynamics, a deterministic nature for the microstructural evolution during phase separation is scrutinized. The deterministic nature is caused by an interfacial-tension-gradient (solutal Marangoni force), which can lead to directional movement of droplets as well as hydrodynamic instabilities during phase separation.

Polymer Injectivity: Investigation of Mechanical Degradation of Enhanced Oil Recovery Polymers Using In-Situ Rheology

Water soluble polymers have attracted increasing interest in enhanced oil recovery (EOR) processes, especially polymer flooding. Despite the fact that the flow of polymer in porous medium has been a research subject for many decades with numerous publications, there are still some research areas that need progress. The prediction of polymer injectivity remains elusive. Polymers with similar shear viscosity might have different in-situ rheological behaviors and may be exposed to different degrees of mechanical degradation. Hence, determining polymer in-situ rheological behavior is of great significance for defining its utility. In this study, an investigation of rheological properties and mechanical degradation of different partially hydrolyzed polyacrylamide (HPAM) polymers was performed using Bentheimer sandstone outcrop cores. The results show that HPAM in-situ rheology is different from bulk rheology measured by a rheometer. Specifically, shear thickening behavior occurs at high rates, and near-Newtonian behavior is measured at low rates in porous media. This deviates strongly from the rheometer measurements. Polymer molecular weight and concentration influence its viscoelasticity and subsequently its flow characteristics in porous media. Exposure to mechanical degradation by flow at high rate through porous media leads to significant reduction in shear thickening and thereby improved injectivity. More importantly, the degraded polymer maintained in-situ viscosity at low flow rates indicating that improved injectivity can be achieved without compromising viscosity at reservoir flow rates. This is explained by a reduction in viscoelasticity. Mechanical degradation also leads to reduced residual resistance factor (RRF), especially for high polymer concentrations. For some of the polymer injections, successive degradation (increased degradation with transport length in porous media) was observed. The results presented here may be used to optimize polymer injectivity.

Performance Evaluation of STARPAM Polymer and Application in High Temperature and Salinity Reservoir.

Based on the properties of high temperature and salinity reservoir, the water-soluble polymer with good heat resistance and salt tolerance can be obtained through copolymerization between 2-acrylamide-2-methyl sulfonate monomer (AMPSN) and acrylamide monomer (AM) in water. The star shaped stable complexes (STARPAM) with the star nucleus of β-CD are prepared by living radical polymerization, which can improve the viscosity and change the percolation characteristics of the polymer in porous media. In the article, the performance of the STARPAM (star-shaped polymer) with heat resistance and salt tolerance was evaluated by comparing the viscosification property, heat and salt resistance, calcium and magnesium tolerance, and long-term thermal stability of STARPAM (star-shaped polymer) with those of HPAM (partially hydrolyzed polyacrylamide) and MO-4000 (linear polymer). The results of physical simulation experiment showed that the viscosity of the STARPAM is 3.3 times that of MO-4000 and 4 times that of HPAM under the conditions of mineralization degree of 20000 mg/L, concentration of 1500 mg/L, and 75°C, which indicated that heat resistance and salt tolerance of the STARPAM are excellent. Oil displacement experiments showed that STARPAM can enhance oil recovery by 20.53% after water flooding, and the effect of oil displacement is excellent. At present, 19 wells were effective with a ratio of 95.2%. Compared with before treatment, the daily liquid production increased by 136 m3, daily oil production increased by 44.6 t, water cut decreased by 4.67 percentage points, and flow pressure decreased by 1.15 MPa.

Research on polymer solution rheology in polymer flooding for Qikou reservoirs in a Bohai Bay oilfield

This study explored the potential applications of three newly modified polymers [a linear polymer, a hydrophobic association of partially hydrolyzed polyacrylamide (HAHPAM), and a polymer–surfactant] as flooding agents in a specific oilfield. Rheological measurements were performed to examine the rheological performances of the three polymers under reservoir conditions. Their stability, viscoelasticity, and propagation properties were analyzed under simulated reservoir conditions. Propagation performance analyses were conducted in a sandpack model to study the propagation behavior of the three polymers in porous media. The results of the rheological study showed that the HAHPAM and polymer–surfactant exhibited high viscosity at low shear rates (deep reservoir), and all three showed acceptable viscosity with good injectivity at high shear rates (near wellbore area). In oscillatory deformation tests, the HAHPAM and polymer–surfactant showed a predominantly elastic behavior. The results of the propagation performance showed the linear polymer and polymer–surfactant could propagate well in porous media, whereas the HAHPAM showed poor propagation behavior. This finding contrasted with rheological tests in which the injectivity of HAHPAM was superior, with high viscosity at low shear rates. The results of the study provided insights either into matching the viscoelastic performance with propagation behavior in porous media, or upon analyzing the suitability of the polymers for flooding throughout a whole process under “from injectivity to propagation” considerations.

Flow of a Cross-Linking Polymer in Porous Media

Heterogeneous reservoirs often have poor sweep efficiency during flooding. Although polymer flooding can be used to improve the recovery, in-depth diversion might provide a more economical alternative. Most of the in-depth diversion techniques are based on the propagation of a system that forms a gel in the reservoir. Premature cross-linking of the system prevents the fluid from penetrating deeply into the reservoir and as such reduces the efficiency of the treatment. We studied the effect of using a polyelectrolyte complex (PEC) to (temporarily) hide the cross-linker from the polymer molecules. In addition to studying the cross-linking process in bulk, we demonstrated its behaviour at the core scale (1 m length) as well as on the pore scale. The gelation time in bulk suggested that the PEC could effectively delay the time of the cross-linking even at high brine salinity. However the delay experienced in the core flood experiment was much shorter. Tracer tests demonstrated that the XL polymer, which is a mixture of PEC and partially hydrolyzed polyacrylamide, reduced the core pore volume by roughly 6.2% (in absolute terms). The micro-CT images showed that most of the XL polymer was retained in the smaller pores of the core. The large increase in dispersion coefficient suggests that this must have resulted in the creation of a few dominant flow paths isolated from each other by closure of the smaller pores.

Impact of Mechanical Degradation on Polymer Injectivity in Porous Media

Polymer flooding is an established enhanced oil recovery (EOR) method; still, many aspects of polymer flooding are not well understood. This study investigates the influence of mechanical degradation on flow properties of polymers in porous media. Mechanical degradation due to high shear forces may occur in the injection well and at the entrance to the porous media. The polymers that give high viscosity yields at a sustainable economic cost are typically large, MW > 10 MDa, and have wide molecular weight distributions. Both MW and the distributions are altered by mechanical degradation, leading to changes in the flow rheology of the polymer. The polymer solutions were subjected to different degrees of pre-shearing and pre-filtering before injected into Bentheimer outcrop sandstone cores. Rheology studies of injected and produced polymer solutions were performed and interpreted together with in situ rheology data. The core floods showed a predominant shear thickening behavior at high flow velocities, which is due to successive contraction/expansion flow in pores. When pre-sheared, shear thickening was reduced but with no significant reduction in in situ viscosity at lower flow rates. This may be explained by reduction in the extensional viscosity. Furthermore, the results show that successive degradation occurred which suggests that the assumption of the highest point of shear that determines mechanical degradation in a porous media does not hold for all field relevant conditions.

Understanding the flow behaviour of copolymer and associative polymers in porous media using extensional viscosity characterization: Effect of hydrophobic association

Associative polymer (AP) and hydrolyzed polyacrylamide (HPAM), the two commonly used polymers for heavy oil recovery, are reported to exhibit very different flow behaviour in porous media despite having similar shear viscosity. The kind of hydrophobic association (intramolecular or intermolecular) that AP exhibit is concentration dependent and will influence both shear and elongational flow in the porous media. To understand flow behaviour of these two polymers in porous media, the role of hydrophobic association on shear and extensional rheology and its effect on the resistance factor (RF) and residual resistance factor in porous media are investigated over a non‐associating HPAM polymer. The results suggest that shear rheology and the Deborah number cannot explain the porous media flow behaviour. However, direct measurements of extensional properties using a capillary breakup extensional rheometer have shown the marginal difference between two polymers at a lower concentration (1000 ppm) and the considerable difference at a higher concentration (2000 ppm), indicating an intramolecular and intermolecular association, respectively. These results are in accordance with porous media observations where both polymers have shown a similar RF at 1000 ppm. Whereas, at 2000 ppm AP showed a much higher RF at low/intermediate fluxes, and a similar RF at high flux, suggesting the transformation from intermolecular association to intramolecular association. The significant drop in the extensional viscosity at high strain rates after exhibiting the maxima explains this behaviour.

Capillary breakup extensional rheometry of associative and hydrolyzed polyacrylamide polymers for oil recovery applications

ABSTRACTHigh molecular weight polymers used for heavy oil recovery exhibit viscoelasticity that can influence the oil recovery during chemical enhanced oil recovery. Different polymers having similar molecular weight and shear rheology may have different elongation flow behavior depending on their extensional properties. Displacing slugs are more likely to stretch than shear in tortuous porous media. Therefore, it is critical to seek an analytical tool that can characterize extensional parameters to improve polymer selection criteria. This article focuses on the extensional characterization of two polymers (hydrolyzed polyacrylamide and associative polymer) having identical shear behavior using capillary breakup extensional rheometer to explain their different porous media behavior. Maximum extensional viscosity at the critical Deborah number and Deborah number in porous media classified the associative polymer as the one having high elastic‐limit. Extensional characterization results were complemented by significantly higher pressure drop, marginally increased oil recovery of associative polymer in porous media. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46253.

Distribution and Presence of Polymers in Porous Media

In order to better utilize the residual polymers formed after polymer flooding, the distribution and the presence of the polymers after polymer flooding were studied. This paper studied the vertical and plane distribution of the hydrophobically-associating polymer in addition to measuring the parameters after polymer flooding, which is important for numerical reservoir simulation. The results showed that the polymers mainly enter into the high permeability zone and distribute in the mainstream line area with only a small portion in the wing area. Based on the comparison of various experimental methods, double-slug experiments were chosen to measure the inaccessible pore volume and retention, which is considered to be the most accurate, most time-consuming and most complex method. Following this, we improved the processing method of experimental data by reducing it to one experiment with two parameters. At the same time, we further enhanced the accuracy of the experimental results. The results show that at 1750 mg/L, the inaccessible pore volume of the polymer is 25.8%. When the detention is 68.2 µg/g, the inaccessible pore volume constituted 22% of the total polymer, with the other 77.7% being the dissolved polymer. Moreover, the static adsorption and dynamic detention were measured, with the results showing that the static adsorption is larger than dynamic detention. Therefore, in the numerical reservoir simulation, using the static adsorption capacity instead of the dynamic detention is unreasonable. The double-slug method was chosen since it is more accurate for the determination of various parameters. Meanwhile, in order to enhance the accuracy of results, we improved the treatment of data.

Pressure Transient Behavior for Alternating Polymer Flooding in a Three-zone Composite Reservoir

Alternating polymer flooding has achieved great attractions recently in oil industry, however, the research of pressure analysis in alternating polymer flooding reservoir is rare. This work presents a numerical pressure analysis method of three-zone composite model for formation evaluation. A new numerical pressure analysis model (three-zone composite model) is established by considering diffusion, convection, shear, and inaccessible pore volume, which is based on the rheology experiments. Based on this model, the type curves are then developed and sensitivity analysis is further conducted. The type curves have seven regimes in three-zone composite model. The characteristic is the obvious upturn of pressure derivative curve in transient regime between low concentration and high concentration polymer solution. Formation parameters can be interpreted by history matching and formation evaluation can be conducted based on this model. As an important part of formation evaluation, formation damage as a result of adsorption of polymers in porous media is evaluated by comparing the interpreted permeability with the original value before polymer flooding. The field test data proves that this proposed method can accurately evaluate reservoir characteristics in alternating polymer flooding reservoirs, which emphasizes the potential application of this method in petroleum industry.

A Comprehensive Combination of Apparent and Shear Viscoelastic Data during Polymer Flooding for EOR Evaluations

We present a comprehensive workflow to obtain the best insights into the viscoelastic behavior of polymers. Viscoelasticity is depicted in most cases by the current commercially available polymers used for EOR applications. The phenomenon is debated to be one of the reasons for additional oil recovery during polymer flooding applications. It is somehow accepted that polymer increases volumetric sweep efficiency owing to improved mobility ratio. Recently researches have explained that flooding polymers in porous media with elastic characteristics could recover additional oil, due to the improved microscale oil displacement (pore-scale). This study focuses on the analysis of polymer viscoelasticity based on single-phase core, sand-pack and capillary tube (CT) experiments coupled with their detailed rheological characterization, in order to evaluate polymer behavior in porous media. A combination of hydrolyzed polyacrylamides (HPAM) polymers as well as a bio polymer is presented throughout this evaluation. The evaluation of the data is addressed on the basis of pressure drop across the pores, separating the shear associated pressure by the extensional thickening associated pressure. Apart from that, viscoelastic dependence of the converging-diverging geometry has been experimented. Based on the observed behavior through porous media, HPAM polymers are compared with bio polymers. Moreover, the behavior of solutions with induced mechanical degradation (pre-sheared) is compared with non-sheared solutions. Similarly, concentrations with different polymer solutions are evaluated. The results obtained in this work allow for additional understanding of polymer solutions behavior in flooding applications. Furthermore The results support the definition of optimized workflows to assess their behavior under flow through porous media. Finally this evaluation helps to describe the parameter that defines polymer viscoelastic properties.

Corrigendum: Flow characteristics of three enhanced oil recovery polymers in porous media

Corrigendum: Flow characteristics of three enhanced oil recovery polymers in porous media

Flow characteristics of three enhanced oil recovery polymers in porous media

ABSTRACTThis article presents an experimental study aiming to explore the relationship among rheological properties, flow characteristics in porous media, and enhanced oil recovery (EOR) performance of three typical EOR polymers. The results suggest that xanthan gum exhibits a very pronounced shear‐thinning behavior, which is probably also the reason explaining its moderate adsorption extent within porous media (thickness of adsorbed layer, e = 3.1 μm). The advanced viscoelastic properties coupled with the less adsorption extent compared to the hydrophobically modified copolymer (HMSPAM) allow xanthan gum to establish a “piston‐like” displacement pattern and lead up to 49.4% original oil in place (OOIP) of the cumulative oil recovery during polymer flooding. Regarding HMSPAM, the significant permeability reduction of the porous media induced by multilayer adsorption (e = 5.6 μm) results in much higher drive forces (ΔP) in the extended waterflooding stage, which further raises the cumulative oil recovery by 18.5% OOIP. In general, xanthan gum and HMSPAM totally produced 84% OOIP which is 15% higher than the extensively used EOR polymer, hydrolyzed polyacrylamide (HPAM), under the same experimental conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41598.

Experimental and Numerical Study of Gel Particles Movement and Deposition in Porous Media After Polymer Flooding

Gel particle, a promising conformance control technology, is recently applying to after-polymer-flooding reservoirs by reusing the remaining polymer in porous media. However, there is no available numerical model which is useful for simulating the conformance control. A series of lab experiments are conducted to explore the main characters of gel particles movements after polymer flooding. Four main mechanisms, namely, swelling, synergy with remaining polymer, shear breaking, and deformation migration, are recognized and described by mathematical formulas. Based on the physical experiments, a numerical model is established to simulate gel particles propagation after polymer flooding. In particular, gel particles are treated as an additional component in aqueous phase. The interaction between the particle gels and the remaining polymer is simplified by aqueous viscosity relationship and particle gel grain size variation. Two transport forms, plugging and deformation migration, are embodied in the model, and the local pressure gradient controls which form the propagation belongs to. The retention of particle gels will cause pore volume decrease and therefore reduce the permeability of thief zones to bypassing water to less swept zones. An iterative method is employed to decouple the gel particle profile control model, which is robust and fairly time-saving. In particular, the flow model is numerically solved by the IMPSAT method and the gel particles continuity equation is explicitly solved by using an operator splitting technique. The newly developed model is validated by history matching results of 1D experiments and actual application case. The results suggest that the presented model is helpful to optimize parameters for profile control for gel particle profile control technology.

Flow of Hydrophobically Modified Water-Soluble Polymers in Porous Media: Controlled Resistance Factors vs. Flow-Induced Gelation in the Semidilute Regime

Summary The associative properties of hydrophobically modified water soluble polymers (HMWSPs) are attractive for improved oil recovery (IOR) because of both their enhanced thickening capability, compared with classical water-soluble polymers (for mobility-control applications), and their permeability-reduction, or plugging, ability (for well-treatment applications). In previous works, we have studied the injectivity of HMWSP made of sulfonated polyacrylamide backbones and alkyl side chains in the dilute regime and have shown, in particular, that it was largely governed by adsorption. In this paper, we report new experimental data on the injectivity of the same class of HMWSP solutions in the semidilute regime. From membrane filtration tests at imposed flow rate, we have first observed the formation of a filter cake made of HMWSP physical gel, which remained largely permeable to polymers. Our observations are compatible with the creation of channels within the gel. This leads to a gel-filtration process, entailing modifications of the solution's viscosimetric properties, which can be explained by a rearrangement of the intra- and interchain hydrophobic bonds in the solution. The second part of our work consisted of injectivity tests in model granular packs. We have performed comparative experiments in porous media with variable permeabilities, but at the same shear rate in the pore throats. Results show that, above a critical permeability kC, or a critical pore-throat radius rpC, HMWSP injection led to stable resistance factors, with values close to the solution's viscosity, and that, at less than kC or rpC the very high resistance factors observed suggest that flow-induced gelation of the HMWSP takes place. Furthermore, resistance factors measured over the core internal sections are compatible with an in-depth formation of the gel. These insights could be of use for designing HMWSP better suited to mobility-control operations and for tuning HMWSP-injection conditions for profile/conformance-control operations.

Rheology of a New Sulfonic Associative Polymer in Porous Media

Summary For hydrophobically associative polymers, incorporating a small fraction of hydrophobic monomer into a hydrolyzed polyacrylamide (HPAM) polymer can promote intermolecular associations and thereby enhance viscosities and resistance factors. In this paper, we investigate the behavior of a new associative polymer in porous media. The tetra-polymer has low hydrophobic-monomer content and a molecular weight (Mw) of 12–17 million g/mol. Total anionic content is 15–25 mol%, including a few percent of a sulfonic monomer. This polymer is compared with a conventional HPAM with 18–20 million g/mol Mw and 35–40% anionic content. Rheological properties (viscosity vs. concentration; and shear rate and elastic and loss moduli vs. frequency) were similar for the two polymers [in a 2.52% total dissolved solids (TDS) brine at 25 °C]. For both polymers in cores with permeabilities from 300 to 13,000 md, no face plugging or internal-filter-cake formation was observed, and resistance factors correlated well using the capillary-bundle parameter. For the HPAM polymer in these cores, low-flux resistance factors were consistent with low-shear-rate viscosities. In contrast, over the same permeability range, the associative polymer provided low-flux resistance factors that were two to three times the values expected from viscosities. Moderate shear degradation did not eliminate this effect—nor did flow through a few feet of porous rock. Propagation experiments in long cores (up to 157 cm) suggest that the unexpectedly high resistance factors could propagate deep into a reservoir—thereby providing enhanced displacement compared with conventional HPAM polymers. Compared with HPAM, the new polymer shows a significantly higher level of shear thinning at low fluxes and a lower degree of shear thickening at high fluxes.

Swelling of polymers in porous media

The swelling of polymers in random matrices is studied using computer simulations and percolation theory. The model system consists of freely jointed hard sphere chains in a matrix of hard spheres fixed in space. The average size of the polymer is a nonmonotonic function of the matrix volume fraction, phi(m). For low values of phi(m) the polymer size decreases as phi(m) is increased but beyond a certain value of phi(m) the polymer size increases as phi(m) is increased. The qualitative behavior is similar for three different types of matrices. In order to study the relationship between the polymer swelling and pore percolation, we use the Voronoi tessellation and a percolation theory to map the matrix onto an irregular lattice, with bonds being considered connected if a particle can pass directly between the two vertices they connect. The simulations confirm the scaling relation R(G) approximately (p-p(c))(delta(0))N(nu), where R(G) is the radius of gyration, N is the polymer degree of polymerization, p is the number of connected bonds, and p(c) is the value of p at the percolation threshold, with universal exponents delta(0)(approximately = -0.126+/-0.005) and nu(approximately = 0.6+/-0.01). The values of the exponents are consistent with predictions of scaling theory.