Flow Behavior Of Polymer Solutions Research Articles

Experimental investigation of flow diversion and dynamic retention during polymer flooding in high salinity fractured carbonates using CT imaging

The successful record of polymer flooding in improving oil production from sandstone reservoirs has encouraged the expansion of its application in carbonate reservoirs. However, the existence of natural fractures, high permeability contrast, and harsh conditions of carbonate reservoirs provide significant challenges for achieving an optimized performance of polymer flooding. It is crucial to establish an appropriate polymer that can offer an optimum flow behavior for in-depth mobility control under reservoir conditions. This study presents in-situ saturation monitoring to evaluate the mobility control effect and identify the flow diversion during polymer injection in high salinity fractured and unfractured carbonate rocks. A synthetic polymer, acrylamido tertio-butyl sulfonate (ATBS) was used and prepared in 200,000 ppm brine salinity. The flow behavior of polymer solution was investigated in bulk rheology tests followed by single-phase core flooding experiments. The flooding apparatus was coupled with a CT scanner to produce 3D images for determining the fluid saturation distribution and inaccessible pore volume (IPV) in real time. Accordingly, flow diversion across fracture-matrix system during polymer injection and the dynamic retention after brine post-flush were identified. The flow experiments showed a shear thickening behavior for the injected polymer solution in the fractured core and no degradation was noticed under in-situ conditions. Based on the fluid saturation profiles, the established flow resistance in the fracture region was prominent to induce flow diversion from the fracture into the matrix. Compared to the case in unfractured rock, the IPV in the fractured rock was approximately 2.5 times higher which was at 53% after 1 PV injection. An additional 23% of IPV was subsequently penetrated upon a continuous polymer injection for 5 PV. In post-flush stage, the fractured core retained about 87% of the injected polymer solution at 1 PV which was then minimized to 7% after 10 PV injection. The entrapped polymer in the fractured core was potentially induced by hydrodynamic retention. This work ascertained the potential of polymer flooding to effectively sweep the fractured carbonates at high salinity environment under certain circumstances for a better conformance.

Experimental study on the flow and heat transfer behavior of polymer solutions in the closed liquid ring vacuum pump system

The closed liquid ring vacuum pump system, which mainly includes the liquid ring vacuum pump and the heat exchanger, is widely used for gas pumping in various industries. In this paper, the energy saving effect in the liquid ring vacuum pump and the flow and heat transfer behavior in the shell-and-tube heat exchanger are investigated for aqueous solutions of rigid xanthan gum (XG) and flexible Polyacrylamide (PAM), and the effects of the concentration, Reynolds number, polymer conformation and flow geometry on the flow behavior of polymer solutions are studied. Results show that, despite the significant differences in molecular conformation and rheological properties between XG and PAM, the similar energy saving rate, about 1.5 ∼ 17.5%, is obtained in the liquid ring vacuum pump. However, in the shell-and-tube heat exchanger, XG solutions exhibit the more obvious pressure drop enhancement and heat transfer reduction than that of PAM solutions for the same concentration. Furthermore, due to the polymer shear degradation, the shaft power in the liquid ring vacuum pump decreases first and then stabilizes, conversely, the flow resistance decreases and the flow rate increases in the heat exchanger. The great difference in the flow condition between the intense rotating gas–liquid two-phase flow field and the gentle liquid pipe flow causes the different flow behavior for XG and PAM solutions.

A polymer flooding mechanism for mature oil fields: Laboratory measurements and field results interpretation

Although polymer flooding has been widely studied in the literature on oil recovery, many questions remain about the technique's action mechanisms. It is widely accepted that the process is based on increasing viscosity of the aqueous phase (injected fluid). The polymer can also act secondarily by reducing the relative permeability to water. Fields that are markedly heterogeneous, highly depleted or that contain fluids with strong salinity are not good candidates for the process. To overcome these restrictions, the most recent applications have used more resistant polymers, with higher molar masses, injected in larger quantities, to preserve the level of viscosity under these adverse conditions. However, a pilot test in a field under adverse conditions showed surprising results and unexpected pressure abnormality, even with small quantities of partially hydrolyzed polyacrylamide (HPAM) with relatively low molar mass (6 × 106 g/mol). This paper reports the investigation of the prevailing mechanism responsible for these unexpected results, by means of laboratory tests of flow in porous media and rheological analysis of fluids and hydrodynamic diameter of polymer molecules. The Salt effect (NaCl) on polymer solutions was researched by rheology and particle size analysis at 25 and 50 °C. The results showed that mechanical/hydrodynamic retention prevails over polymer adsorption at the rock, with the former being caused by the increase in the polymeric hydrodynamic volume in fluid dilution processes. Besides this, increased temperature was found to favor greater hydrodynamic volume under tested conditions, while salinity had little influence. The results also shed new light on the flow behavior of polymer solutions in porous media, particularly in polymer injection for enhanced oil recovery from mature fields.

Statement of Removal

ABSTRACTPolymer flooding is an attractive branch of chemical enhanced oil recovery techniques. Regrettably, chemical and mechanical degradation reduces the effectiveness of polymer flooding. This paper explores the effects of silica nanoparticles on flow behavior of polymer solution in porous media by employing both rheological experiments and numerical simulations. Experimental results indicate that dispersed silica nanoparticles in polymer solution are responsible for polymer adsorption reduction and the solution viscosity improvement. Simulation results revealed that if the injectant has some dispersed silica nanoparticles, the cumulative heavy oil recovery and breakthrough time will be bettered compared to the conventional polymer flood.

An Investigation of Polymer Adsorption in Porous Media Using Pore Network Modelling

Polymer injection in hydrocarbon reservoirs has been of great interest in petroleum engineering as an enhanced oil recovery method. In order to have a reliable injection plan, an accurate estimation of polymer behaviour is required to control the fluid flow in porous media. However, it is difficult to calculate the flow properties of polymer solutions—known as non-Newtonian fluids—in porous media, due to variable viscosity at different shear rates. Adsorption of polymer molecules onto the rock surface decreases the available cross-sectional area of polymer solution, therefore at a constant rate, the shear rate increases. As a result, it is important to investigate how polymer adsorption can affect the polymer solution flow behaviour in porous media. Moreover, prior to any polymer injection plan, the amount of adsorbed polymer should be calculated, due to the high cost of polymers. In the present study, pore network modelling was used to investigate the effect of polymer adsorption on flow behaviour of polymer solutions in porous media. To achieve this goal, a simple pore was constructed to adequately represent the real structure of the porous medium. It was then validated by simulation of Newtonian fluid flow in the network and comparison of the calculated flow properties with the experimental data. After validation, the pore network was used for simulation of non-Newtonian fluid flow in porous media. The experimental apparent viscosity of non-Newtonian fluid was used for verification of the procedure and the developed network. The apparent viscosity of non-Newtonian was calculated successfully using macroscopic properties of the rock sample and measured bulk properties of non-Newtonian fluid. The effect of polymer adsorption on calculation of non-Newtonian fluid apparent viscosity was then investigated. It was shown that the polymer adsorption process plays an important role in calculation of polymer solution apparent viscosity. The results reveal that polymer adsorption cannot be neglected, especially in near well-bore areas where the adsorption is high. Finally, the effect of wettability in calculating the total amount of adsorbed polymer volume was studied. The results suggest that neglecting the rock’s wettability can result in an overestimation or underestimation of the amount of adsorbed polymer.

Study on Flow Parameters Measurement Experiment of Polymer Solution in Porous Media

Due to the complexity of porous media and viscoelasticity of polymer solution, the flow behavior of polymer solution in porous media is more complex than that in the rheometer, and the flow regular pattern of polymer solution in porous media directly affects the formulation of polymer flooding projects. This paper designs experiment on flow parameters measurement of polymer solution (partially hydrolyzed polyacrylamide) in porous media, and the regular pattern of influence on resistance factor, residual resistance factor and flow viscosity in porous media caused by core permeability, polymer concentration, polymer molecular weight and polymer injection rate was given. The followings are the results: even for the same batch core with similar parameters, due to reasons such as natural fractures which could lead to comparatively large difference of core parameters between the same batch of core, thus in order to ensure the reliability of experiment data, it is necessary to detect core quality before core flooding experiment. Core end effect has significant effect on the results of core flooding experiment, it suggests that we should eliminate the effect of core end effect when carry out core flooding experiment, otherwise it is difficult to obtain valid experiment data. There exists a critical polymer concentration, when polymer concentration is lower than critical concentration, resistance factor is basically equal to apparent viscosity; when polymer concentration is higher than critical concentration, resistance factor is far less than apparent viscosity and the difference value increases with the increase of polymer concentration. Flow viscosity of polymer solution in porous media is far less than apparent viscosity in the rheometer and when polymer concentration increases, the increase extent of flow viscosity is far less than the increase of apparent viscosity. Results of this research are of great importance for enhancing flooding effect and guiding oilfield production.

Numerical investigation of spinneret geometric effect on spinning dynamics of dry‐jet wet‐spinning of cellulose/[BMIM]Cl solution

ABSTRACTIn this study, the effect of spinneret geometry, including the entrance angle α of the entrance channel, the length Ls, and the diameter D0 of the exit channel, on the spinning dynamics of dry‐jet wet‐spinning of cellulose/1‐butyl‐3‐methylimidazolium chloride ([BMIM]Cl) solution was simulated by using finite element method. Based on the mathematical model of dry‐jet wet‐spinning established in our previous work (Xia et al., Cellulose 2015, 22, 1963) the radial and axial profiles of velocity, pressure, and shear rate in the spinneret and the profiles of diameter, temperature, and tensile stress in the air‐gap region were obtained. From the simulated profiles, the effect of spinneret geometric parameters on the flow behavior and the pressure drop of polymer solution in the spinneret and the die‐swell ratio near the spinneret was discussed. The entrance angle α of the entrance channel mainly influences the flow behavior of polymer solution in the spinneret and the die‐swell effect near the spinneret. As the decrease of the entrance angle α of the entrance channel, the vortices in the spinneret could be removed and the die‐swell ratio decreases. The increase of the length Ls of the exit channel results in the increase of pressure drop in the spinneret and the decrease of the die‐swell ratio. It is also found that the increase of the diameter D0 of the exit channel reduces the flow velocity of polymer solution and decreases the pressure drop in the spinneret at a constant mass flow rate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43962.

Characterizing the Role of Clay and Silica Nanoparticles in Enhanced Heavy Oil Recovery During Polymer Flooding

Polymer flooding as one of the most effective methods for enhancing oil recovery has a significant effect on tertiary production of reservoirs with poor vertical sweep efficiencies and those which are extremely heterogeneous. Water-soluble polymers are used to both increase the viscosity of water and decrease the mobility ratio of the displaced and displacing fluids. However, due to high amount of polymer adsorption, presence of divalent cations and mechanical degradation, polymer molecules may lose their properties. Hence it is necessary to further improve the displacement effectiveness of polymer flooding. Despite the fact that several ways have been suggested to enhance the performance of polymer flooding, application of nanoparticles in the improvement of rheological properties of the polymer solution used in enhanced oil recovery has not been reported previously and is still an ongoing subject. This paper investigates the effects of nanoparticles on flow behavior of polymer solution in porous media by employing both experimental studies and numerical simulations. The simulation model first is validated against well-controlled laboratory experiment to have reliable predictions of the full-field implementations. The results show that the amount of polymer adsorption and viscosity of polymer solution will improve when the clay or silica nanoparticles is present in the injectant, and accordingly, the cumulative oil recovery and breakthrough time will be bettered. The result of sensitivity analysis demonstrates that polymer molecules are more degradable during polymer flooding compared to nanoparticles-assisted polymer flooding. Based on the validated model, 3D simulations of nanoparticles-assisted polymer field pilot were performed and the results revealed that the cumulative oil recovery, water cut and breakthrough time will improve when the injectant has some dispersed nanoparticles.

Macromol. Mater. Eng. 9/2013

Cover: Extensional rheological properties determine the flow behavior of polymer solutions through porous media. The biopolymer schizophyllan, which experiences such flows in enhanced oil recovery operations, shows drastic changes in its conformational structure depending on the nature of the solvent. As a result, the extensional relaxation time is found to exhibit a strong change in scaling with concentration for solutions in water (in which a triple-helical structure is reported), compared to solutions in DMSO with a random coil structure. Further details can be found in the article by R. De Dier, W. Mathues, and C. Clasen* on page 944.

Thermal properties and side chain crystallinity of styrene and n‐alkyl methacrylate terpolymers

Differential scanning calorimetry method was used for the study of thermal properties of terpolymers of styrene (ST) or methyl methacrylate (MMA) with dodecyl methacrylate and octadecyl methacrylate. Particularly, the interdependencies of the crystallinity content and composition of terpolymers were examined. The increase of the MMA or ST content in terpolymers resulted in the increased glass transition temperatures and decrease of the ratio of crystalline relative to amorphous phase (from 10% for xMMA = 10 mol% to 5.7% for xMMA = 30 mol%, and from 8.5% for xST = 16 mol% to 4% for xST = 40 mol%). These kinds of copolymers are commonly used as flow improvers at low temperatures for lubricating mineral oils; therefore a direct correlation between flow behavior of polymer solutions in mineral oil (pour point) and side‐chain crystallinity of copolymers was examined. Thus, by increasing the proportion of crystalline phases, i.e. the long‐chain alkyl methacrylates in copolymer, the pour point of oil solutions lowers. Thus, the solution of terpolymer with crystalline phase content of 4 mol% displays the pour point of −9°C while in those with crystalline phase content higher than 7 mol% pour point lowers below −30°C. POLYM. ENG. SCI., 53:2299–2307, 2013. © 2013 Society of Plastics Engineers

A hierarchical model for surface effects on chain conformation and rheology of polymer solutions. I. General formulation

The flow behavior of polymer solutions near a solid surface (either neutral or adsorbing) is modeled through a new, hierarchical (macroscopic and microscopic) approach which enables the thermodynamically consistent extension of equilibrium (static) considerations to nonequilibrium (flow) conditions. The approach involves two steps: First, the set of primary, independent, variables defining the state of the system at the macroscopic level is chosen, and a complete set of transport and constitutive equations is constructed for them through a two fluid, Hamiltonian model. In the present work, the macroscopic variables include the polymer chain concentration, the macroscopic fluid velocity, and the conformation tensor (defined as the tensor of the second moment of the chain end-to-end vector). The governing equations involve the (extended) free energy or Hamiltonian of the system, H, and are valid both in the bulk of the fluid and in the interfacial region. Thus, to solve them one needs to specify H. This is done in a second step, by invoking a microscopic model, which consistently takes into account the simultaneous effect on chain conformations of both the solid boundary and the imposed flow field. Solid boundary effects are taken into account in the solution of a diffusion equation for the chain propagator G(r,n;r0) which represents the weighted probability that an n-segment long chain which starts at r0 will end at position r. Flow field effects are taken into account through the definition of a generalized propagator G′(r,n;r0,α), which further depends on the apparent strain tensor α, representing chain deformation effects due to flow. The present part of the paper describes the general formulation of the approach and its relevance with previous works. Results from applying the methodology to the case of a polymer solution flowing past a purely repulsive surface (a wall) are presented in the second part of this work.

Rheological characterization of the dilatant flow behavior of highly substituted hydroxypropylmethyl- cellulose solutions in the presence of sodium lauryl sulfate

The flow behavior of aqueous solutions of three highly substituted, hydrophobic hydroxypropylmethylcelluloses (HPMC) in mixtures containing the anionic surfactant sodium lauryl sulfate (SLS) was investigated both rheo-mechanically and rheo-optically. For the first time it was possible to demonstrate dilatant flow in these systems, a phenomenon which is otherwise only known of some suspensions and associative thickening solutions. Without addition of SLS, the aqueous HPMC solutions showed the predicted flow behavior of polymer solutions, and the Cox–Merz rule was fulfilled. With the addition of SLS to these HPMC solutions, the least hydrophobic HPMC displayed no dilatancy. The solutions of a more hydrophobic HPMC with SLS exhibited on the one hand an increase in viscosity, and on the other hand shear thinning as well as shear thickening. The most hydrophobic HPMC displayed more clearly the effects of an SLS-dependent viscosity increase and the appearance of dilatant flow. At constant HPMC concentration (0.5% w/w), a maximum increase in viscosity (factor 15) was observed in the critical micelle concentration range for SLS. By rheo-optical measurements it was possible to detect an unusually pronounced alignment of the polymer segments as well as a sharp increase in the birefringence values, even before the macroscopic occurrence of dilatant flow. According to the existing network theories, this behavior of the aqueous solutions of highly substituted HPMCs in mixture with SLS has been interpreted as a shear-induced transition from intra-molecular to intermolecular interactions.

Measurement of pressure loss in the flow of polymer solutions through packed beds of particles

Flow behavior of polymer solutions through packed beds of particles, which are used as a model of porous media, is experimentally examined. Two packing patterns are prepared and the test fluids used here are aqueous solutions of polyacrylamide (PAA) at three different concentrations. In the measurement of pressure loss, it is observed that the curve of pressure loss makes a sudden change at the critical flow rate. Below the critical flow rate, the pressure loss depends on the shear property of the fluids and can be expressed by the modified Darcy’s law applying the power law model to the shear viscosity of fluids. Beyond the critical flow rate, however, the transient elongational property of the fluids dominates the flow behavior in packed beds of particles and yields the excess pressure loss for the PAA solutions.

Measurement of pressure loss in the flow of polymer solutions through wavy channels

In order to examine the flow behavior of polymer solutions through porous media, the measurement of pressure loss and the experiment for flow visualization were carried out with wavy channels as one of the model channels of porous media. The test fluids used are aqueous solutions of polyacrylamide (PAA) with two different concentrations. The occurrence of the excess pressure loss, which was not due to the effect of the centrifugal force, was found for the PAA solutions. The relations between the friction factor ratio and the Deborah number were similar to that obtained for the flow through porous media. Furthermore, the results of the flow visualization suggest that the elongational property of the PAA solutions is connected with the occurrence of the excess pressure loss.

Measurement of Pressure Loss in the Flow of Polymer Solutions through Packed Beds of Particles

Flow behaviour of polymer solutions through packed beds of particles, which are used as a model of porous media, is experimentally examined. Two packing patterns are prepared and the test fluids used here are aqueous solutions of polyacrylamide(PAA) at three different concentrations. In the measurement of pressure loss, it is observed that the curve of pressure loss makes a sudden change at the critical flow rate. Below the critical flow rate, the pressure loss depends on the shear property of the fluids and can be expressed by the modified Darcy's law applying the power law model to the shear viscosity of fluids. Beyond the critical flow rate, however, the transient elongational property of the fluids dominates the flow behaviour in packed beds of particles and yields the excess pressure loss for the PAA solutions.

ポリマー水溶液の多孔質媒体内流動における振動効果の解析

In this paper, vibration theory of elastic body is applied as an analogy to the quantitative analysis of resistance factor of polymer solution measured when it flows through porous media.Resistance against flow of polymer solution through porous media is not caused only by viscosity of polymer solution, but also affected by the energy dissipation by experiencing rarefaction and compression of polymer solution while flowing alternately in the throat connecting pores and in the open pore spaces. Euler Equation is modified to express such elastic resistance of polymer solution caused by the oscillation of normal stress in the fluid. Flow equation comprised of both Euler Equation and Darcy Equation is introduced to calculate both elastic and viscous resistances against flow through porous media. New equation is applied successfully to demonstrate the dilatant flow behavior of polymer solution in the flooding experiences through a capillary tube packed by glass beads and through Berea sand cores.Diffusion equation modified to express the vibration effect of viscoelastic fluid is applied to solve the pressure loss of polymer solution flowing through porous media. Quantitative analysis of the resistance factor of flow of polymer solution through porous media is presented by the use of analytical solution of diffusion equation.

溶液の粘弾性を考慮したポリマー攻法の解析 その２．一次元ポリマー攻法の室内実験

To study how the viscoelastic flow behavior of polymer solution described in Part. 1 (ref. 1) had an effect on oil-recovery performance, 1 D flood experiments were carried out with glass-bead packed cores. Two white mineral oils of viscosity about 25mPa•s and 50mPa•s were used as displaced fluids. In each experiment, water and polymer floods were done with the same core at a relatively-high flooding velocity above 16μm/s. In polymer floods, polymer concentration of effluents was measured by the spectrophotometric method of M.W. SCOGGINS and J.W. MILLER.In polymer floods, oil was recovered faster as flooding velocity became faster. In high flooding velocity, interstitial velocity of polymer solution in the core becomes high and shear rate for flow becomes larger, too. The viscoelastic flow behavior of polymer solution that increased its viscosity with increasing shear rate was thought to improve mobility ratio and make oil recovery faster. By analysis of polymer-concentration histories of effluents, water bank was observed to be produced from the core before breakthrough of injected polymer solution. This water bank was thought to originate from mobile water which was initially present in the core before the flood. The histories of pressure of oil and water phase at the center of cores during flood experiments were measured separately with semi-permeable filters made of teflon and ceramics. Oil pressure could be measured well, but the method to measure water pressure was remained to be a problem.These data obtained in this study will be compared with calculated results by the simulater in the next paper.

溶液の粘弾性を考慮したポリマー攻法の解析 その３ フラクショナルフロー理論を用いた挙動予測

A new mathematical model was constructed to express flow behavior of polymer solution for two-phase flow of oil and the solution. By combining the fractional flow theory proposed by G. A. Pope with this model, a simple simulator was developed to predict performances of polymer flood. In this simulator, permeability reduction owing to adsorption of polymer molecules was modeled by reduction of hydraulic radius for flow of the solution. Two parameters (C*, mc) dependent on pore structure and fluid relaxation time were used to calculate the viscoelastic flow behavior of polymer solution.Calculated performances were compared with experimental data of 1D polymer flood described in the previous paper (ref. 5). The simulator could reproduce the experimental data well when viscoelastic flow behavior was assumed. By model calculations, the viscoelastic effects of polymer solution on oil recovery were foand to (1) increase flow resistance in two-phase flow, (2) make breakthrough saturation of polymer solution higher by shifting fractional flow curve to higher saturation, and (3) make oil recovery faster, therefore.

EFFECT OF DEFORMATION SEQUENCE ON RHEOLOGICAL BEHAVIOUR AND MECHANICAL DEGRADATION OF POLYMER SOLUTIONS

The flow behaviour of polymer solutions of non-hydrolyzed polyacrylamide and Xanthan was investigated in two rectangular and similar plexiglas models containing 3 cylindrical enlargements of the same dimensions. These three enlargements were located successively at the mid point of the first model length, whereas they were equally spaced along the second one. Only non-hydrolyzed polyacrylamide polymer solutions have shown viscoelastic behaviour in these plexiglas models. However, the behaviour of these polymer solutions in the first model was different from that in the second one. The multipass mechanical degradation of the non-hydrolyzed polyacrylamide polymer solutions was studied extensively in the two plexiglas models. It was shown that, at high flow rates, the multipass mechanical degradation was stronger in the second model than in the first one. The mechanical degradation in model 1 converges with that in model 2 as the flow rate decreases. The difference in flow behaviour and mechanical degradatio...

Retention and Flow Characteristics of Polymer Solutions in Porous Media

Abstract Retention and flow characteristics of a solution containing Pusher 700, a high-molecular-weight, partially hydrolyzed polyacrylamide, were studied partially hydrolyzed polyacrylamide, were studied in an 86-md core made by compacting Teflon powder. The quantity, of polymer retained during linear displacement experiments ranged from 10 to 21 mu gm/gm for polymer concentrations of 100 to 500 ppm in 2-percent NaCl solutions. Nearly all retention ppm in 2-percent NaCl solutions. Nearly all retention was attributed to mechanical entrapment because of low polymer adsorption on the Teflon surface. Flow rate affected polymer retention. In increase in velocity was accompanied by polymer retention. Polymer was expelled when the flow rate was Polymer was expelled when the flow rate was reduced. Inaccessible pore volume was about 19 percent of the total pore volume. percent of the total pore volume.Resistance factors in different sections of the core ranged Pam 2 to 10 /or solutions of 100 to 500 ppm polymer concentration in 2-percent NaCl. ppm polymer concentration in 2-percent NaCl. Permeability reduction resulting from polymer Permeability reduction resulting from polymer retention produces the resistance factor in most of the core at a velocity of 3.2 ft/D. Resistance factors in the Teflon cores were two to three times lower than those reported for natural porous media where polymer is also retained by adsorption. Introduction The search for a low-cost, effective mobility control agent is currently focused on dilute aqueous solutions containing partially hydrolyzed polyacrylamides or polysaccharides. Rheological polyacrylamides or polysaccharides. Rheological properties have been studied, including the properties have been studied, including the effects of polymer concentration, shear rate, electrolyte concentration, and type of electrolyte. Correlation of rheological data and models with the flow behavior of polymer solutions in porous media has been complicated by the many interactions that occur between the complex porous matrix and the polymer solutions. Some data have been correlated using non-Newtonian rheological models to describe the variation of fluid viscosity with the apparent shear rate that the fluid experiences as it flows through the tortuous paths in porous media. These correlations have adjustable parameters determined from the particular set of parameters determined from the particular set of data used to develop the correlation. Investigators studying partially hydrolyzed polyacrylamide solutions observed apparent polyacrylamide solutions observed apparent viscosities 5 to 20 times the values measured in a conventional viscometer at the shear rates believed to exist in the porous media. These viscosity increases were not anticipated from the rheological behavior of the fluids. Pye introduced the concept of the resistance factor to quantify this effect. Burcik observed a decrease in the mobility of brine in a Berea sandstone disk that had been previously contacted with partially hydrolyzed previously contacted with partially hydrolyzed polyacrylamide. The mobility reduction persisted polyacrylamide. The mobility reduction persisted even after 100 PV of brine had been flushed through the disk. Burcik concluded that polymer molecules retained in the pore structure by adsorption or mechanical entrapment were hydrophillic and restricted the flow of water. Gogarty made an extensive experimental study of partially hydrolyzed polyacrylamide solutions in porous media and concluded that these polymer porous media and concluded that these polymer solutions reduced the permeability of the porous media. He noosed that polymer retention in natural cores occurred by mechanical entrapment and adsorption. Both mechanisms contributed to the resistance and residual or flushed resistance factors observed with polyacrylamide solutions. Other evidence of interactions between the polymer solution and the porous matrix was found. polymer solution and the porous matrix was found. Adsorption of polymer molecules on the surface of materials present in the porous matrix has been demonstrated in batch adsorption experiments. Material-balance calculations made on the streams entering and leaving porous media following step changes in concentrations show retention of polymer molecules in the porous media. polymer molecules in the porous media. A dependence of polymer retention on flow rate has been reported. Szabo devised a set of static and flow experiments in which polymer adsorption was held to a low level by using silica sand with a small surface area. Mechanical entrapment was found to be the dominant retention mechanism in short sand packs. packs. SPEJ P. 111