Polymer Retention Research Articles

The Use of Tracer Data To Determine Polymer-Flooding Effects in a Heterogeneous Reservoir, 8 Torton Horizon Reservoir, Matzen Field, Austria

Summary Polymer-injection pilot projects aim at reducing the uncertainty and risk of full-field polymer-flood implementation. The interpretation of polymer-pilot projects is challenging because of the complexity of the process and fluids moving out of the polymer-pilot area. The interpretation is increasingly more complicated with the heterogeneity of the reservoir. In the polymer pilot performed in the 8 Torton Horizon (TH) reservoir of the Matzen field in Austria, a polymer-injection well surrounded by a number of production wells was selected. A tracer was injected 1 week before polymer injection. The tracer showed that the flow field in the reservoir was dramatically modified with increasing amounts of polymer injected. Despite short breakthrough times of 4 to 10 weeks observed for the tracer, polymer breakthrough occurred only after more than 12 months although injection and production rates were not substantially changed. The tracer signal indicated that the reservoir is heterogeneous, with high flow velocities occurring along a number of flow paths with a limited volume that are strongly connecting the injection and production wells. By injecting polymers, the mobility of the polymer-augmented water was reduced compared with water injection, and led to flow diversion into adjacent layers. The tracer response showed that the speed of the tracer moving from injection to production wells was reduced with increasing amount of polymer injected. This response was used to assess the changes of the amount of water flowing from the injection well to production wells. After a match for the tracer curve was obtained, adsorption, residual resistance factor (RRF), and dispersivity were calculated. The results showed that, even for heterogeneous reservoirs without good conformance of the pilot, the critical parameters for polymer-injection projects can be assessed by analyzing tracer and polymer response. These parameters are required to determine whether implementation of polymer injection at field scale is economically attractive. Along the flow path that is connecting injection and production well, as shown by the tracer response, an incremental recovery of approximately 8% was achieved. The polymer retention and inaccessible pore volume (IPV) in the reservoir were in the same range as in corefloods. Incremental oil recovery caused by acceleration along the flow path was estimated at approximately 20% of the overall incremental oil production caused by polymer injection and 80% was attributed to improved sweep efficiency.

Modelling of polymer retention during low concentrated HPAM polymer flooding in the heterogeneous reservoirs

The polymer retention has been regarded as one of the major concerns in the operating process. The polymer retention includes adsorption, mechanical entrapment, and hydrodynamic retention. Retention by mechanical entrapment occurs when large polymer molecules become lodged in narrow flow channels. A number of studies found that considerable amounts of emulsions are retained at junctions between two different permeability zones, with maximum retention at the front portion of the low permeability zone. Large permeability reductions are also found. These papers imply the strong dependence of retention on the permeability. In addition, researches associated with polymer flooding have identified the characteristic of polymer retention. Overall, polymer retention is attributed to both adsorption onto surfaces and entrapment within small pores. Adsorbed polymers induce greater resistance to flow in low-permeability layers than in high-permeability layers, although the radius of penetration is greater for high-permeability layers. Traditionally, retention has been modelled as only adsorption using Langmuir's adsorption model, even though macromolecules are retained in different locations within pore spaces. Therefore, the model of polymer retention needs to be modified with respect to pore size, which is strongly related to permeability. [Received: February 25, 2014; Accepted: January 14, 2015]

Polymer flow through water- and oil-wet porous media

The effect of wettability on polymer behavior in porous media is investigated through a series of synthetic polymer floods conducted in water- and oil-wet Bentheim and Berea sandstone cores. A new experimental setup is used in which the core effluent polymer concentrations are not measured during polymer flooding, but instead are passed through a capillary tube that is connected to the core outlet. Using the notion of intrinsic viscosity, an approximate expression is presented that can be used to determine the breakthrough time of the injected polymer solution. In addition, polymer adsorption, inaccessible pore volume, and apparent viscosities are evaluated for all cores and wetting conditions. In general, in the presence of residual oil, the oil-wet cores display the lowest degree of polymer retention (Berea) and the lowest inaccessible pore volume-IPV (Bentheim). The largest wettability impact on the polymer behavior in porous media appears to be for the Berea formation; polymer retention in oil-wet cores decreases 90% and IPV 52% compared to the corresponding amounts for the water-wet ones. On the other hand, the estimated polymer retention and IPV values appear to be similar for the oil- and water-wet Bentheim cores, this is attributed to questionable wettability alteration.

Characterisation of phenolic resin and nanoclay admixture and its effect on impreg wood

Bulking treatment with low molecular weight phenol formaldehyde (LmwPF) resin has been found to successfully enhance the properties of low-density wood but emit higher formaldehyde. Incorporation of nanoparticle to the phenolic matrix could possibly reduce the use of high concentration LmwPF and thus lower the formaldehyde emission (FE) without adversely affecting the other properties. The aim of the study was to examine the characteristics of LmwPF resin and nanoclay admixture and determine its effects on the performance of impreg wood. Montmorillonite nanoclay nanomer (0.5–1.5 % w/w based on solid PF) was dispersed in LmwPF resin (10–20 % w/v) using ultrasonication technique. The dispersion of nanoclay in LmwPF was examined using X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). XRD and TEM analyses confirmed that the nanoclay dispersion in the resin was in exfoliated form. Air-dried sesenduk (Endospermum diadenum) wood was impregnated with these admixtures using vacuum pressure process followed by curing at 150 °C for 30 min. The FE, dimensional stability and strength properties were evaluated and compared with impreg wood treated solely with LmwPF. The results showed that the polymer retention and density of the LmwPF/nanoclay-impregnated samples were higher than the LmwPF-impregnated samples. This admixture had successfully bulked the cell wall of the wood and imparted higher dimensional stability to the treated wood. The modulus of rupture and modulus of elasticity, compressive stress and hardness of the LmwPF/nanoclay impreg were more superior compared to the LmwPF impreg. The admixture was also found to be able to reduce the FE compared to LmwPF resin.

Effect of polymer concentration on the polymer adsorption-induced permeability reduction in low permeability reservoirs

This study presented the effect of polymer adsorption-induced permeability reduction on oil recovery, particularly in low permeability system. The polymer injecting experiments were conducted in a quarter of five-spot pattern with concentrations generally applied. Especially, by using the field oriented two-dimensional sandstone, we attempted to analyze the combined effect of polymer retention for concentration and high velocity near injection on oil recovery.Particularly in low permeable sandstone, oil recovery was not proportionally enhanced with increase in polymer concentration, rather decreased at concentrations above 1,000 ppm in this experiment. This could be understood by polymer adsorption phenomena corresponding to concentrations. The polymer adsorption layer formed at high concentration clogged effective pore radius by up to 59.8%, compared to clean sandstone and the permeability greatly decreased from 56 to 1.5 mD, resulting in rather decreased oil recovery. For this reason, there should be an optimum concentration for maximizing the oil recovery. It was also confirmed by shear rate analysis. At high concentration, the shear rate near injection where has the highest velocity was greater than critical rate. This means that polymer molecules adsorbed to mono-layer of adsorption by hydraulic force, and the adsorption became additionally thicker and hindered the oil flow.

Study on the Impact of Polymer Retention in Porous Media on Further Surfactant-Polymer Flood

Polymer flood gains expansive popularity as a promising EOR method in various oilfields worldwide. However, there are still substantial amount of resources underground after polymer application. To further enhance oil recovery, secondary chemicals are sometimes utilized to sweep the remaining hydrocarbons to maintain the consistent development of oilfields. In this paper, a series of experiments are established and conducted to explore the feasibility of surfactant/ polymer flooding applied to a polymer flooded reservoir, and also the influence of polymer retention in porous media to enhance the oil recovery performance of subsequent chemical drive. The data of the experiments suggest that surfactant/polymer flooding owns a very good potential as a subsequent EOR technique, and that polymer retention in pores helps block underground water channels, improving greatly the sweeping efficiency of secondary chemical flood.

Microvisual investigation of polymer retention on the homogeneous pore network of a micromodel

Abstract A new experimental technique is reported for visualization of polymer retention on the solid surfaces of porous media. Etched silicon micromodels with well-characterized pore networks were used during single-phase flow to examine the retention of 0.2 wt% partially hydrolyzed polyacrylamide (HPAM) solution. Image analysis included an image subtraction and an RGB-based global thresholding technique for quantification of polymer retention/adsorption. Results are reported as the percentage of porosity occupied by immobile polymer. Three factors were investigated including the salinity of displacing water, the change of wettability of the micromodel surface, and mechanical degradation of polymer. With respect to salinity in displacing water, the experiment confirmed that 5 wt% NaCl results in less polymer retention (6.3±0.3%) than without NaCl (7.5±0.3%). The increase in Na + concentration was sufficient to induce contraction of the size of the flexible HPAM molecules and, therefore, decrease the thickness of polymer adsorption on the grain. Two methods were used to alter the initially strongly water-wet surface of the micromodel. Wettability was changed by the deposition of crude oil and CTAB (cetyl trimethylammonium bromide) in aqueous solution. The micromodels treated using crude oil and CTAB showed polymer retention of 15.0±0.3%% and 5.0±0.3%%, respectively. Oil-wet micromodels aged by crude oil showed larger polymer retention than the polymer retention on water-wet micromodels (7.5±0.3%). Otherwise, the polymer retention on the CTAB treated micromodel was lower than the polymer retention on the water-wet micromodel. Finally, polymer solution flowed through a 7 µm filter was tested. Average polymer retention was 4.3±0.3% and this is 3.2±0.3% point lower than the value of unfiltered polymer solution. Further investigation of microgels within pore networks provided a chance to demonstrate that a size and structural flexibility of microgel leading to a transition from mobile to immobile conditions.

Integrated Analysis of Permeability Reduction Caused by Polymer Retention for Better Understanding Polymer Transport

Polymer retention is one of the most important factors to govern polymer propagation through porous media, determining whether successful or not. The focus of previous studies has been limited to polymer concentration loss caused by the retention; not only change in polymer concentration, but also reduction in reservoir permeability is the main issue for theoretical transport study. Due to the lack of accuracy of Langmuir isotherm describing the polymer retention mechanisms, this study proposes a new type of matching interpretation method to correlate the permeability reduction factors from experiments to permeability. In order to solve the problem of poorly matching results between estimation and observation, use of nonadsorptive constant conditionally selected in matching process was made. Based on the threshold permeability reduction factors, approximate critical permeability can be calculated to which nonadsorptive constant would be applied. Results showed significant improvements in the estimation of permeability reduction for both low and high permeability cores. In addition, effects of permeability reduction on polymer transport in field scale were analyzed using the proposed matching model. Thus, not only does this interpretation method help to evaluate prediction for accurate flow behavior, but also unwanted risk can be evaluated.

Literature review of implemented polymer field projects

Polymer flooding is a mature enhanced oil recovery (EOR) technology applied in field projects as early as the late 1950s. There exists extensive amount of experience, know-how and learning related to field implementation of polymer with respect to logistics, engineering design, reservoir properties and monitoring & surveillance in the literature. The aims of this paper are twofold. It is firstly to compile an up-to-date data base for implemented pilot/field polymer injection projects reported in the literature over the last 50 years. Based on the compiled data qualitative information and statistics are presented regarding differences between projects being classified as technical successes compared to the discouraging cases reported. Secondly, to assure that that planning and implementation of upcoming polymer projects can leverage on the large amount of experience and lessons learned built up in the industry over the years. 40 of the reported polymer projects were classified as successes and 6 were assessed discouraging. 46 projects have been performed in the U.S.A. (64 %) followed by 6 in Canada and P.R. China (8 %), 4 in Germany (5.6 %), etc. 66 projects were implemented onshore and only 6 offshore. HPAM was used as polymer in 92 % of the cases and the rest were using biopolymer (1 projects used a hydrophobic associative polymer). Data analysis reveals that 4 of the discouraging projects experienced significant drop in injectivity during the flood. The projects using emulsion-based synthetic polymers had more challenges related to injectivity compared to the cases using the powder type synthetic polymers. 3 of the discouraging cases injected only 17 % pore volume (PV) compared to 34 % PV slug size for the successful projects. Average permeability in the successful projects was 563 mD vs. only 112 mD in the discouraging cases. The success rate for projects implementing polymer injection in secondary mode was higher than when injecting polymer in tertiary mode. No major differences could be identified between successful and discouraging projects with respect to polymer concentration, resistance factor, residual resistance factor, polymer retention, well spacing, formation temperature and oil viscosity. The number of challenges and issues observed in the production wells due to polymer breakthrough and production was in general low and mostly related to increased tendency for corrosion and formation of emulsions in the production system.

Field vs. Laboratory Polymer-Retention Values for a Polymer Flood in the Tambaredjo Field

SummaryDuring a polymer flood, polymer retention can have a major impact on the rate of polymer propagation through a reservoir, and consequently on oil recovery. A review of the polymer-retention literature revealed that iron and high-surface-area minerals (e.g., clays) dominate polymer-retention measurements in permeable rock and sand (>100 md). A review of the literature on inaccessible pore volume (IAPV) revealed inconsistent and unexplained behavior. A conservative approach to design of a polymer flood in high-permeability (>1 darcy) sands would assume that IAPV is zero. Laboratory measurements using fluids and sands associated with the Sarah Maria polymer flood in Suriname suggested polymer retention and IAPV values near zero [0±20 μg/g for retention and 0±10% pore volume (PV) for IAPV]. A procedure was developed using salinity-tracer and polymer concentrations from production wells to estimate polymer retention during the Sarah Maria polymer flood in the Tambaredjo reservoir. Field calculations indicated much higher polymer-retention values than those from laboratory tests, typically ranging from approximately 50 to 250 μg/g. Field cores necessarily represent an extremely small fraction of the reservoir. Because of the importance of polymer retention, there is considerable value in deriving polymer retention from field results, so that information can be used in the design of project expansions.

Mechanical Properties and Flow Behavior of Polymers for Enhanced Oil Recovery

The mechanical properties and flow behavior in porous media of three different polymer systems including a hydrophobically modified acrylamide-based copolymer (HMSPAM), a partially hydrolyzed polyacrylamide (HPAM), and a polysaccharide (xanthan gum) were evaluated to establish their functional differentiation as mobility control agents in enhanced oil recovery (EOR). The rheological properties of the polymers were described by the power-law model to investigate their non-Newtonian behavior. The first normal stress difference (N1) and Weissenberg number (We) were also used to compare their elastic properties. The experimental results showed that, at comparable shear viscosity, HMSPAM exhibited significant elasticity compared to HPAM and xanthan gum. Shear resistance tests indicated that all of the polymers experienced an extra stress when converging into a capillary tube due to the “entrance effect.” Xanthan gum was the most mechanically stable polymer. Moreover, HMSPAM showed the superior reformability which was quantified by the regained viscosity with relaxation time. This could be explained by the rapid re-association of the hydrophobic interactions. Sandpack flood tests indicated that HMSPAM rendered extremely high mobility control ability during polymer flooding suggesting its potential in EOR. However, this polymer also experienced significant retention within the porous media (potential injectivity and plugging problems), which may be attributed to the formation of bulky associative polymer networks. In this work, UV spectrometry was employed to monitor the concentration of the produced polymer solutions and quantify the polymer retention within porous media. This analytical approach offers great reliability and simplicity. It was concluded that the use of a particular polymer system depends on the oil reservoir conditions and the target EOR application.

Effect of Concentration on HPAM Retention in Porous Media

Summary This paper investigates the effect of hydrolyzed polyacrylamide (HPAM) polymer concentration on retention in porous media by use of both static and dynamic measurements. Consistent results by use of these two methods show that different polymer-retention behaviors exist in dilute, semidilute, and concentrated regions. In both the dilute and concentrated regions, polymer retention has little dependence on concentration. In contrast, in the semidilute region, polymer retention is concentration dependent. If a porous medium is first contacted sufficiently with dilute polymer solution to satisfy the retention, no significant additional retention occurs during exposure to higher HPAM concentrations. On the basis of the experimental results, a concentration-related retention mechanism is proposed that considers the orientation of the adsorbed polymer molecules and the interaction between molecular coils in solution. By use of this model, we explain why polymer retention does not show much dependence on concentration in the dilute and concentrated regimes. Further, in the semidilute region, we explain how moderate coil interactions lead to mixed adsorbed-polymer orientation and magnitude on rock surfaces, and retention becomes concentration dependent. In field applications of polymer and chemical floods, reduced polymer retention may be achieved by first injecting a low-concentration polymer bank.

Experimental Investigation of Polymer Adsorption-Induced Permeability Reduction in Low Permeability Reservoirs

The polymer retention during polymer flooding causes reduction in pore throat size which can be detrimental to oil recovery. Especially, in low permeability reservoir unlikely in high permeability system, EOR effect of polymer flooding would not excel comparing to water flooding because of the polymer adsorption onto grain surface. This phenomenon is more significant as higher concentration of polymer solution is injected. In this study, we investigated oil recovery process during polymer flooding for a quarter of 2D 5-spot pattern of low permeability sandstone slab, in which the injected polymer solution flows in different shear rates corresponding to streamlines. The results showed that the ultimate recovery was 1.9 times higher in concentration of 1,000 ppm case than 0 ppm. The polymer adsorption layer formed during the flooding reduced the effective permeability of 1,000 ppm polymer solution. Therefore, it facilitated the oil flow and the stage of water-cut reaching 99% was slackened off.

Effects of the Water Absorbability of Superabsorbent Prepared by Graft Copolymerization of Acrylic Acid onto Milk Proteins

Super Absorbent Polymer is a new type of functional polymer material developing at a high speed since the late 70’s. It can absorb water quickly . After absorbing water it becomes a kind of achromatic hydromel, and the absorbed should be: water is hard to remove even under pressure. As a result, it is usually referred as high-absorbent polymer, super absorbent polymer retention or super absorbent polymer unnecessary . This study is concerned methods of preparation and application areas of water absorbency, the influence of the initiating agent and cross-linking agent amount on the water absorbency. When the initiating agent, cross-linking agent ratio were respectively 0. 4% and 0. 2%, the water absorbency was highest. The reversibility of PH is also discussed, as well as the best methods of preparing high-water-absorbent resin cut this.

Investigation on Polymer Adsorption and Retention in a Polymer Flooded Reservoir

During polymer flooding, certain amount of polymer would be lost. Polymer retention causes sweep volume expanding on one side, it also causes polymer loss on the other. Therefore, it is a very important topic to study the influencing factors of polymer retention. There are many factors affecting polymer retention process. This paper mainly studied the influence from dynamic factors such as polymer solution concentration, injection rate, injection time, injected pv number. This paper investigated the influence of these factors on polymer retention process, and optimized these factors to minimize polymer loss in reservoir.

Use of a novel pH-triggered polymer-gel system for optimal mobility-control applications

AbstractThere are two challenges in using polymers for conformance control applications in the petroleum industry. The first difficulty is to maintain a good injectivity to overcome the large pressure drop caused by the high viscosity of the polymers. Secondly, large polymer volumes required to be injected to compensate for polymer retention in a reservoir. The main objective of this work is to study the viability of using a pH-sensitive polyelectrolyte to alleviate the above two challenges. The results showed that the pH of the swelling medium has great effect on the swelling behavior of poly(acrylic acid) hydrogels. At low pH regime, the viscosity increases gradually as pH increases until certain pH value, ‘critical pH’ is reached. In the second regime and once critical pH value is exceeded, the viscosity increases sharply with the pH. This is followed by independency of the viscosity on pH, in the third regime. It was found that this sensitivity to the pH varies with the change in crosslink density and shear rates. At pH=4 (before the gellation), the sample (Carbopol 981) which has the lowest crosslink density exhibits the highest viscosity among the three samples. After the gellation (PH=8), the rheological behavior is reversed for the highest crosslinked density polymer (EZ-4) and the lowest crosslinked density polymer (981) which contradicts with the well known swelling ratio-crosslink density relation. It is concluded that the examined polymers are good candidates for mobility control applications. They can also be used for temporary zonal isolation since they can be easily broken down with mild acid wash and flowback

Application of PEO/Cofactor System on Papermaking Process for Recycled Fibers

Ionic trash in furnish decreases retention and drainage performance of the microparticle retention system using recycled fibers in closed papermaking system. Two retention systems, such as the microparticle system and the PEO/cofactor system, were compared and analyzed to improve retention. The PEO/cofactor system achieved similar retention performance at low addition level as the microparticle system. Optimum ratio of PEO/cofactor dual polymer system was 1:10. Ash retention was increased when using the fixing agent. As the TMP ratio increased, the PEO/cofactor system was more efficient in retention and drainage than the other system. The high molecular weight and non-ionic polymer retention system had less effect on flocculation hindrance than the traditional electrostatic retention system.

The study on Characteristics of Surface-Active Polymer

Through the indoor comparative experiments, this paper studied the viscosity and surface tension of surface-active polymer, and calculated the critical micelle concentration, the surface adsorption capacity, molecular occupied area, and other parameters. Through comparing with intermediate molecular weight polymer, it is found out that surface-active polymer has characteristics of high viscosity and its viscosity is higher than common polymer under the same concentration. As a new type of polymer, surface-active polymer can reduce the tension and present a certain activity. The critical micelle concentration of surface-active polymer is 0.2532 g/L, the surface adsorption capacity is 1.678×10 -10mol.cm -2,and the molecule occupies an area of 0.9899 nm 2 .This theme also studied the emulsifying power and the characteristic of static and dynamic adsorption. The results show that the agents have approved emulsifying power with only 38% of the excluded water during 30 days. The static adsorption capacity of surface-active polymer is 1.92 mg/g. Under the same condition, its dynamic retention volume is greater than the amount of polymer retention.

Metal-ion retention properties of water-soluble amphiphilic block copolymer in double emulsion systems (w/o/w) stabilized by non-ionic surfactants

Metal-ion retention properties of water-soluble amphiphilic polymers in presence of double emulsion were studied by diafiltration. Double emulsion systems, water-in-oil-in-water, with a pH gradient between external and internal aqueous phases were prepared. A poly(styrene-co-maleic anhydride) (PSAM) solution at pH 6.0 was added to the external aqueous phase of double emulsion and by application of pressure a divalent metal-ion stream was continuously added. Metal-ions used were Cu2+ and Cd2+ at the same pH of polymer solution. According to our results, metal-ion retention is mainly the result of polymer–metal interaction. Interaction between PSMA and reverse emulsion globules is strongly controlled by amount of metal-ions added in the external aqueous phase. In addition, as metal-ion concentration was increased, a negative effect on polymer retention capacity and promotion of flocculation phenomena were produced.

Activated Carbon Water Purification Filter Prepared by Wet Molding with a DualPolyelectrolyte Retention System

amboo-based activated carbon fibers were fabricated into paper- and cylinder-shaped composites using a simple wet molding technique combined with a dual polymer retention (DPR) system. The as-prepared activated carbon cylinders possessed high practical utility and were assessed for water purification purposes. They achieved the effective removal of colloidal organic contaminants in model tap water. In addition, calcium sulfite powder and carboxymethyl cellulose fiber were successfully embedded into the activated carbon cylinder. The resulting composite accomplished the efficient removal of residual hypochlorite compounds and lead ions. The simple wet-molding method combined with the DPR system is well suited to mass production, and the activated carbon cylinder is a promising material for future water purification systems.