On the Effect of Polymer Elasticity on Secondary and Tertiary Oil

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On the Effect of Polymer Elasticity on Secondary and Tertiary Oil Recovery Santhosh K Veerabhadrappa, Ankit Doda, Japan J Trivedi, and Ergun Kuru Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 30 Oct 2013 Downloaded from http://pubs.acs.org on November 5, 2013

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Industrial & Engineering Chemistry Research

On the Effect of Polymer Elasticity on Secondary and Tertiary Oil Recovery Santhosh K. Veerabhadrappa‡, Ankit Doda, Japan J. Trivedi∗, Ergun Kuru University of Alberta, Edmonton, AB Canada [email protected], [email protected], [email protected] [email protected]

ABSTRACT: Typically, a polymer for enhanced oil recovery (EOR) is selected based on the viscosity range or average molecular weight, concentration, and brine composition, besides other reservoir properties. There is not much emphasis given on how the elasticity of polymers could enhance the oil recovery. In this study, in an effort to find a systematic approach for selecting the best polymer for water flooding, effect of molecular weight distribution (MWD), a direct measure of polymer's elasticity was studied on oil recovery performance. Individual effect of elasticity of polymers on oil recovery, breakthrough and overall recovery, and residual resistance factor (RRF) was determined by keeping the viscosity constant and varying the elasticity during secondary and tertiary recoveries experiments. Within two different groups of polymers each with similar average molecular weight studied here, nearly 10% higher recovery for highest elastic polymer was observed during secondary recovery; whereas for tertiary flood ~ 6% higher recovery with ~5 times higher RRF value was observed for highest elastic polymer solution studied here. Results have shown that average molecular weight by itself might not be the best criteria to select the optimum polymer fluid composition for polymer flooding operations. Polymer elasticity should be weighted more than the average molecular weight as it could correspond to higher sweep efficiency due to the stretching of polymer along the pores. Considering the polymer elasticity or MWD together with average molecular weight seems to be a better approach for achieving higher oil recovery performance at lower polymer concentrations.

1. INTRODUCTION Over the past 5 decades or so, polymers have been used extensively for enhanced oil recovery (EOR) or improved oil recovery (IOR). Polymer flooding has been applied to reservoirs under a wide range of operating ∗

Corresponding Author : Japan J Trivedi E-mail: [email protected] ‡ Now with EOR Processes, Energy Division, Saskatchewan Research Council

ACS Paragon Plus Environment


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environments such as, reservoir temperature and pressure, permeability, geology, oil viscosities, variable net pay thicknesses and brine chemistry etc., to name a few.1 A large number of commercially available polymers, both synthetic and biopolymers, have been tested in EOR/IOR applications. The two most commonly used are the partially hydrolyzed polyacrylamide (HPAM), synthetic polymer, and xanthan biopolymer.2 Continued improvements in technology and expertise in the field of polymer aided EOR operations in recent times have made polymer flooding more and more economical but it still offers considerable scope for further improving the technology. Key property of EOR polymers that makes polymer flooding one of the most widely used chemical EOR techniques is its viscoelasticity. Laboratory and field experiments along with numerical simulations have shown that the viscoelastic characteristics of polymer solutions help improve polymer flood efficiency.3-9 Han et al. 4, in their study using core flooding experiments and numerical simulation, concluded that displacement efficiency of a polymer flood operation would reach its maximum when the viscoelastic property of polymer solution is brought into full play. Extensive literature is available aimed towards understanding the role played by viscoelasticity of polymers in improving polymer flood efficiency. But the individual effect of elasticity of viscoelastic polymers on improved oil recovery remains vaguely understood. Field pilots have shown an increase in oil recovery with increasing the concentration and molecular weight of polymer solutions. Yang et al.10 have described the role of higher molecular weight polymer samples (i.e., higher viscosity samples) in achieving higher oil recovery in Daqing oil field, China. But it is also necessary to take elasticity into account in conjunction with viscosity while selecting a polymer for EOR. Hence, it becomes imperative to delineate the individual effect of elasticity on improved oil recovery in order to have a better screening model for any polymer flood operation. One way of doing that is by testing the performance of polymer samples of same viscosity but different elasticity. Veerbhadrappa et al.11 studied the mechanism of viscous fingering for viscoelastic polymers in two-phase horizontal immiscible flow systems in terms of elasticity. They confirmed that higher elastic polymers are better suited for achieving higher sweep efficiency with stable displacement fronts. Depending on the elasticity of polymer viscous fingering patterns 2|2 0


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can be different at the displacement front. A polymer that has many molecular weight components with a range of molecular weight distribution is said to be polydisperse and on the other hand, a polymer with only one molecular weight component is said to be monodisperse.12 Polymers with similar average molecular weight but different molecular weight distribution will have same viscosity but different elasticity. Thus, MWD is used as a measure of elasticity of polymer solutions. In this work, an attempt has been made to study the recovery performance of HPAM polymers having identical average molecular weights but with a range of MWD values. Radial and linear core flooding experiments were conducted to study the secondary and tertiary recovery performances.

2. EXPERIMENTAL PROCEDURE 2.1 Materials 2.1.1 Polymers Four different grades FLOPAAM polymers, AB005 V, 3130 S, 3330 S and 3630 S, supplied by SNF SAS in dry powder form, were used in the preparation of four HPAM solutions. These polymers are anionic and water-soluble with a degree of hydrolysis of 25-30 mole % Table 1 shows these four HPAM polymer grades with their average molecular weights. By keeping same average molecular weight but different MWD, it was possible to prepare polymer solutions with similar shear viscosity and variable elastic characteristics (rheology is presented in the next section). The average molecular weight of polymer blend is given by the equation11,13-15.

, ,

(1)

Where, , is the average molecular weight of the blend, is the weight fraction of polymer grade i and , is the average molecular weight of polymer grade i.

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MWD is well represented by polydispersity index (I), which is the ratio of the weight average molecular weight to the number average molecular weight, given by equation 2.16 Higher value of polydispersity index implies wider molecular weight distribution and hence higher elasticity.

(2)

Even though polydispersity index cannot be used as an absolute measure of MWD, it is true without an exception that, higher polydispersity index indicates wider MWD. Statistical explanation given by Sheu17 states that, polydispersity index is a good measure of the width of molecular weight distribution of polymers. Due to the unavailability of Mn data for the polymer grades used, polydispersity index of polymer solutions were not calculated. Instead, the elastic nature of these solutions was quantified using their elastic modulus. By adjusting the weight fraction of polymer grades by trial and error method, it was possible to come up with two different groups of HPAM samples, one having a similar average molecular weight of approximately 2,000,000 and second with 8,000,000. Table 2 shows weight fractions of pure grade polymers used prepare different HPAM samples, denoted as HPAM-1 to HPAM-7 and their average molecular weight. The first four HPAM blends (HPAM-1 to HPAM-4) have the same average molecular weight of 2,000,000 Dalton. Similarly, HPAM-5, HPAM-6 and HPAM-7 were prepared to have the same average molecular weight of 8,000,000 Dalton. Samples with same average molecular weight should have similar shear viscosity; whereas different MWD imply different elastic characteristics. This will be further tested in the rheological section next. All polymer solutions were prepared by adding calculated quantities of HPAM grades directly to deionized water. HPAM grades were added in the decreasing order of their molecular weights and mixed using a magnetic stirrer at 300 rpm for 24 hours until it became completely transparent and no filtration was needed. 2.1.2 Mineral Oil Light mineral oil used in the experiments had a viscosity of 27.8 cp and a specific gravity of 0.83 at 24 ºC. It is composed mainly of paraffins and cyclic paraffins.

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2.1.3 Porous Media Potters Industries Inc. supplied SPHERIGLASS A-GLASS 3000 grade glass beads were used as porous media in all flooding experiments. Glass beads had a particle size distribution of 30-50 microns and a specific gravity of 2.5. The absolute permeability of the porous medium was found to be 450 mD ± 2%.

2.3 Rheological Characterization Two types of rheology tests were conducted in order to characterize HPAM solutions; viscometry test and oscillation test. A C-VOR 150 Peltier Bohlin rheometer with cone and plate measuring system was used for these tests. Polymer samples were placed in between a stationary plate, with a diameter of 60 mm, and a rotating upper cone with a 4º angle and a diameter of 40 mm, separated by a gap of 150 µm. All measurements were carried out at room temperature. 2.3.1 Viscometry Test Viscometry tests were carried out at a range of shear rates from 1s-1 to 100 s-1. Figure 1 and Figure 2 show shear stress vs. shear rate and shear viscosity vs. shear rate behavior of HPAM solutions respectively. As seen from the shear stress vs. shear rate plot (Figure 1), HPAM samples follow power law model. Shear viscosity values of HPAM solutions having the same average molecular weight were found to be lying very close to each other (Figure 2). HPAM-1 to HPAM-4 having an average molecular weight of 2,000,000 Dalton show shear viscosity values lower than HPAM-5 to HPAM-7, having an average molecular weight of 8,000,000 Dalton. 2.3.2 Oscillation Test Oscillation tests or frequency sweep tests measure viscoelastic properties such as viscous modulus and elastic modulus as a function of frequency at constant stress. A constant shear stress of 0.04775 Pa was maintained throughout and tests were carried out at a frequency range of 0.01 to 1 Hz. As shown in Figure 3, the viscous 5|2 0



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moduli of HPAM samples 2, 3 and 4 are very close to each other through the frequency range of 1 to 10 rad/s. Viscous modulus of HPAM-1 is slightly lower than the other HPAM samples in the low angular frequency region. However, at angular frequency between 0.5 to 5 rad/s, they all have similar viscous moduli. HPAM-5 to HPAM-7 samples with an average molecular weight 8,000,000 Dalton have identical viscous modulus but greater than that of HPAM-1 to HPAM-4 samples with an average molecular weight 2,000,000 Dalton. Results from Figure 2 and Figure 3 confirm that, HPAM samples with higher average molecular weight will have higher shear viscosity or viscous modulus. The elastic modulus vs. angular frequency graph (Figure 4) shows that among polymers having the average molecular weight 2,000,000 Dalton, HPAM-4 has the highest elasticity followed by HPAM-3, HPAM-2 and HPAM-1. Among polymers having the average molecular weight 8,000,000 Dalton, HPAM-7 has the highest elasticity followed by HPAM-6 and HPAM-5.

2.4 Core Flooding Experiments 2.4.1 Secondary Polymer Flood The main components of the experimental setup include a radial core holder designed to simulate radial flow. The core holder had an internal diameter of 98 mm and a height of 191 mm. It had one injection well located at the center and two production wells at the periphery. The lower 145 mm section of the injection well is perforated. Injection line had a radius of 7 mm and both production lines had a radius of 3.6 mm. Injector and producers were tightly wounded by a screen with 10 micron opening. A constant rate LC-5000 syringe pump for injecting oil and polymer, a pressure transducer for pressure measurements and a data logger for recording pressure data digitally on a computer, graduated measuring jars for collecting and measuring effluents constitute the other essential parts of the experimental set-up. A schematic of the experimental set-up is shown in Figure 5.

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2.4.2 Tertiary Polymer Flood To validate the results of secondary polymer flooding and role of elasticity on tertiary recovery four sets of experiments were performed during linear core flood in a tertiary polymer flood mode. Tertiary recovery experiments were conducted in a cylindrical core holder mounted horizontally to represent the linear flow. The core holder had an internal diameter of 28.57 mm and a height of 152.4 mm. 2.4.3 General Procedure 1. Sandpack preparation: Initially the core holder was tightly packed with dry spherical glass beads with the help of a mechanical vibrator operated by air pressure. 2. Oil Saturation: The core holder was then saturated with mineral oil using a constant rate syringe pump. The volume of oil required to saturate the core holder, which depends on the pore volume, was recorded. For secondary flooding experiments, pore volume of the porous medium was determined using direct method by subtracting the volume of glass beads in the core holder from the bulk volume of the core holder. For tertiary polymer flood experiments, prior to oil saturation water was injected into the core holder to calculate the pore volume and permeability of the core. Pore volume was calculated using material balance between water injected and water collected on the producer side. Permeability was calculated by varying the flow rates till a stable pressure was obtained on each flow rate. Mineral oil was then injected using a constant rate syringe pump. Water pushed by mineral oil was also collected to calculate irreducible water saturation in the core 3. Water Flooding: For tertiary flooding experiments 1 PV of water was injected into the core holder at a constant flow rate of 0.5 ml/min. 4. Polymer Flooding: In secondary flooding experiments, the polymer solution was injected into the radial core holder by using a syringe pump at a constant flow rate of 4 ml/min, while for tertiary flooding the polymer solution injection into the liner core holder was maintained at a constant flow rate of 0.25 ml/min. Effluents (oil + polymer) produced were collected at regular intervals and the volume of oil 7|2 0



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and polymer collected were measured separately. Pressure needed to inject polymer solution was recorded throughout the experiment. Flooding was continued until either the volume of oil produced was too low or the water cut was greater than 95%. Typically the volume of polymer injected was around 2 PV. 5. Extended Water Flooding: For tertiary recovery experiments, finally, extensive water flooding (up to 20 PV) was done to produce remaining oil as well as to check the permeability change due to polymer retention. Residual and Residual Resistance factor was reported. Pressure readings were recorded throughout the experiment using a pressure transducer. 2.4.4 Effective Shear Rate in Porous Media Christopher and Middleman18 suggested the following equation to estimate shear rates in cores.

γ=

3n + 1 4Q 4n A(8kφ )0.5

(3)

Where is shear rate, 1/s; (3n + 1)/4n is a non-Newtonian correction factor for power-law fluids; Q is flow rate, cm3/s; A is cross sectional area of the core, cm2; k is permeability, cm2 and ∅ is porosity. For the type of fluids we have used n values changed between 0.45 and 0.56. For secondary flood, substituting n values of 0.45 and 0.56, k = 450 ± 2% md; φ = 42-44%; A= 63.77-413.62 cm2 (for radial core, area encountered by flow changes as fluid goes from injector to producer); and a flow rate of 4ml/min would yield to shear rate of ~ 10-70 s-1 in porous media. For tertiary flood, substituting n values of 0.45 and 0.56, k = 350-380 md; φ = 42-44%; A= 6.413 cm2; and a flow rate of 0.25ml/min would yield to shear rate of ~ 27-30 s-1 in porous media. 2.4.5 Discussion of Shear thinning in porous media At low velocities in porous media, HPAM solutions generally shows mild shear thinning behavior.3,19-22 Chauveteau et al.21 observed that the permeability reduction remained constant at lower shear rates and then increases as the shear rate increases. The onset of the shear thickening was observed at effective shear rate ~ 100 s-1. 8|2 0


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The effective shear rate in porous media for the experiments conducted for linear core setup, ~26-29 s-1, is well below the effective shear rate for onset of shear thickening as observed by Chauveteau et al.21 For radial core setup this shear rate varied from 10-70 s-1. Note that the permeability and polymer type could influence the onset of shear thickening however; it is safe to assume that the experiments performed in this study are in the effective shear rate of shear thinning. Recently, Seright et al.22 reported resistance factor vs. flux rate using porous media with 3000 to 5000 md permeability and HPAM polymers with molecular weight (M.W) ~ 18-20 millions. They have reported that shear thickening was observed when they used flux rate above 10 ft/day. The Flux rate for the model used in our experimental studies with injection rate of 0.25 ml/min and 4 ml/min were equal to 1.84 ft/day and 0.45 ft/day to 3 ft/day respectively for linear and radial cores that are well below that critical flux value of 10 ft/day reported by Seright et al.22 Comparing our experimental results with the previously published data, we have concluded that flow rates used in our experiments might not be high enough to induce shear thickening effect. 2.4.6 Residual Resistance Factor Residual resistance factor were calculated for this type of linear flooding. Residual resistance factor is defined as the ratio of the permeability to brine before and after the injection of polymer solution.23 RRF is defined as;

FRR =

( kw / µ w )before ( kw )before = ( k p / µ p )after ( kw )after

(4)

Under given flow rate in same core flooding system, RRF is expressed in terms of pressure drops as:

FRR =

( ∆Pw )after ( ∆Pw )before

(5)

Table 4 shows residual resistance factor of all 4 HPAMs for linear core flooding.

3. RESULTS AND DISCUSSION 3.1 Secondary Polymer flood Oil Recovery Performance The variation of cumulative oil recovery as a function of volume of polymer solution injected is shown in 9|2 0



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Figure 6. Of all the polymers with an average molecular weight of 2,000,000 Dalton, HPAM-4, which has the highest elasticity resulted in the highest oil recovery of 75.2% while, HPAM-1, which has the lowest elasticity, resulted in the lowest oil recovery of 64.7%. The elastic modulus of HPAM-4 is 16 times greater than that of HPAM-1 at an angular frequency of 0.1 rad/s and 3 times at an angular frequency of 1 rad/s. Figure 7 and Table 3 summarize the results of the influence of MWD (polydispersity index) and average molecular weight on breakthrough and cumulative oil recovery. The recovery performance of these four polymer samples is in the ascending order of HPAM-1 > HPAM-2 > HPAM-3 > HPAM-4. For all these four polymers, HPAM-1 to HPAM-4, shear viscosity and hence the viscous modulus values are similar within the range of shear rate application as shown earlier in Figure 2 and Figure 3. Hence, the reason for difference in higher ultimate recovery, ~10%, between HPAM-4 and HPAM-1 polymer solution injection could be mostly due to their elasticity difference. Elastic modulus trend as shown in Figure 4 is also in the ascending order of HPAM-1 > HPAM-2 > HPAM-3 >HPAM-4, and correlates well with the trend in oil recovery. Results from recovery experiments using low average molecular weight (2,000,000 Dalton) polymer solutions support the idea that, polydispersity index – a measure of elasticity – can be used to screen a polymer among available same average molecular weight polymers for better EOR performance. In order to confirm this conclusion further, we performed similar experiments using HPAM solutions of high molecular weight (8,000,000 Dalton). Among the three polymers with an average molecular weight of 8,000,000 Dalton, HPAM-7 and HPAM-5 resulted in highest and lowest oil recoveries respectively. The ultimate recovery for HPAM-5 polymer injection was 74.6% and that of HPAM-7 was 86.1%. The ~11% higher recovery in case of HPAM-7 correlated well with the fact that HPAM-7 had higher elastic modulus than HPAM-5. The elastic modulus of HPAM-7 is 4.5 times greater than that of HPAM-5 at angular frequency of 0.1 rad/s and 2 times higher at an angular frequency of 1 rad/s. The difference in oil recovery performance of HPAM-3 and HPAM-4 is very minimal in terms of breakthrough recovery as well as final recovery (Figure 7). This can be attributed to lower elasticity difference as shown in Figure 4, which indicates small difference in MWD widths. Therefore, along with the previous 10 | 2 0


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observation of an increase in elastic modulus resulting in higher breakthrough and final recoveries (HPAM-1 to HPAM-4 and HPAM-5 to HPAM-7), one can say that there exists an optimal MWD (polydispersity index) beyond which the recovery is not significantly affected by the increase in elastic properties. Conventional polymer flooding field approach assumes that viscoelastic polymers with highest average molecular weight are expected to give better recovery performance. The difference in ultimate recovery between HPAM-5 and HPAM-1 is ~10%, whereas HPAM-5 has four times higher average molecular weight than HPAM-1. It was interesting to see that all three HPAM polymer samples with average molecular weight 8,000,000 Dalton resulted in significantly higher breakthrough recoveries than the ones with average molecular weight 2,000,000 Dalton. The difference in ultimate recovery between HPAM-7 and HPAM-1 is more than 20%, due to the difference in average molecular weight between two polymer samples of four times and difference in elastic modulus of nearly 140 times at an angular frequency of 0.1 rad/s and 13 times at an angular frequency of 1.0 rad/s. However, if the average molecular weight was the only criteria for a polymer to perform better during EOR application, HPAM-5 should have performed better than HPAM-4. But, the final recovery of HPAM-5 polymer injection was not significantly different from that of HPAM-4 despite the fact that HPAM-5 polymer solution has higher average molecular weight (8,000,000 Dalton) than HPAM-4 (2,000,000 Dalton).

3.2 Tertiary Polymer flood Oil Recovery Performance Four HPAM samples (HPAM-1 to HPAM-4) with an average molecular weight of 2,000,000 Dalton were used in linear coreflooding experiments. Linear coreflooding experiments were done in three stages: secondary waterflooding (1 PV) followed by 2 PV of tertiary polymer flooding (HPAM-1 to HPAM-4) and finally an extensive waterflooding for up to 20 PV. Tertiary recovery for HPAM-4 is 33%, which is highest among four HPAM polymers tested. This higher recovery can be attributed to the high value of elasticity of HPAM-4. Since HPAM-1 has the lowest elasticity, it also has the lowest value of tertiary recovery that is 30%. The recovery performance of these four polymer samples is in the ascending order of HPAM-1 > HPAM-2 > HPAM-3 > HPAM-4 and correlates well 11 | 2 0



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with the ascending order of elasticity of HPAM samples as observed in secondary radial core flood experiments in previous section. Similar observations were made in case of radial coreflooding as discussed earlier. One of the advantages of polymer flooding is that polymer pore plugging results into ‘inaccessible pore volume’ and redirects the injected polymer to unswept areas.24 Higher value to RRF for HPAM-4 than other polymer solutions also indicates that polymer elasticity can contribute significantly in the plugging that is taking place for porous media and reduce water-phase permeability. The injection of higher elasticity of polymer solution is likely to have higher tendency to form polymer agglomerates or associations within the porous media, plugging the small pores and reducing permeability. This phenomenon together with adsorption may have resulted into ~ 5 times higher RRF value for highest elastic HPAM polymer solution, therefore could decreases the requirement of viscosity enhancement, and produces more stable viscous front propagation than the lowest elastic polymer solution.

4. Conclusions 1. A rheological characterization study of polymer solutions in association with polymer flooding experiments was conducted as part of the efforts to develop a systematic approach for selecting best polymer for conventional polymer flooding operations. Individual effect of elasticity of polymers on oil recovery was determined by keeping the viscosity constant and varying the elasticity i.e., by having polymers of same average molecular weight but different molecular weight distribution. 2. Within the range of applicable shear in porous media, the reason for difference in ultimate recovery, ~10% during secondary recovery and ~6% during tertiary recovery, between HPAM-4 and HPAM-1 polymer solution could be mostly due to their elasticity difference. For both groups of similar average molecular weight polymers studies, nearly 10% higher recovery for highest elastic polymer was observed during secondary recovery. These results have shown that average molecular weight by itself

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might not be the best criteria to select optimum polymeric fluid composition for water flooding operations. 3. The final recovery of HPAM-5 polymer injection was not significantly different from that of HPAM-4 despite the fact that HPAM-5 polymer solution has higher average molecular weight (8,000,000 Dalton) than HPAM-4 (2,000,000 Dalton), echo the previous conclusion that the molecular weight distribution or elasticity together with average molecular weight seems to be the better approach for formulating optimum polymer solutions with higher oil recovery performance.

Acknowledgements

The authors wish to acknowledge the financial support from NSERC Discovery Grant and the University of Alberta for this research. We also extend our thanks to SNF SAS for polymer samples.

Nomenclature A FR FRR k kw kp I Mw Mn Mw,B ωi Mw,i n φ

λw λp µw µp ∆Pw ∆PP rP

γ

Q

= = = = = = = = = = = = = = = = = = = = = = =

Cross sectional area of the core, cm2 Resistance Factor Residual Resistance Factor Permeability, cm2 Permeability of water, mD Permeability of Polymer, mD Polydispersity Index Weight average molecular weight Number average molecular weight Average Molecular Weight of Polymer Blend Weight Fraction of polymer grade i Average Molecular Weight of Polymer Grade i Flow Behaviour Index Porosity, fraction Mobility of water Mobility of Polymer Viscosity of water, cP Viscosity of polymer, cP Pressure Drop during Water Injection, kPa Pressure Drop during Polymer Injection, kPa Average Pore Diameter, µm Shear rate in porous media, 1/s Flow rate, cm3/s

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(1)

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(2)

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(7)

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(10) Yang, F.; Wang, D.; Wang, G.; Sui, X.; Liu, W.; Kan, C. Study on High-Concentration Polymer Flooding To Further Enhance Oil Recovery. Presented at the SPE Annual Technical Conference and Exhibition, San Antonio, TX, USA, 24-27 September, 2006; paper SPE 101202. (11) Veerabhadrappa, S. K.; Trivedi, J. J.; Kuru, E. Visual Confirmation of the Elasticity Dependence of Unstable Secondary Polymer Floods. Industrial and Engineering Chemistry Research, 2013, 52(18), 6234–6241. (12) Severs, E.T., 1967. “Rheology of Polymers”. New York: Reinhold Publishing Corporation (13) Dehghanpour, H. H. A. Investigation of Viscoelastic Properties of Polymer Based Fluids as a Possible Mechanism of Internal Filter Cake Formation. Master's Thesis, 2008. (14) Dehghanpour, H.; Kuru, E. Effect of Viscoelasticity on the Filtration Loss Characteristics of Aqueous Polymer Solutions. Journal of Petroleum Science and Engineering, 2010, 76 (1-2), 12-20. (15) Urbissinova, T. S.; Trivedi, J. J.; Kuru, E. Effect of Elasticity During Viscoelastic Polymer Flooding: A Possible Mechanism of Increasing the Sweep Efficiency. Journal of Canadian Petroleum Technology,

2011, 49(12), 49-56. (16) Zang, Y. H.; Muller, R.; Froelich, D. Influence of Molecular Weight Distribution of Viscoelastic Constants of Polymer Melts in the Terminal Zone. New Blending Law and Comparison with Experimental Data. Polymer, 1987, 28 (9), 1577-1582. (17) Sheu, W. S. Molecular Weight Averages and Polydispersity of Polymers. Journal of Chemical Education, 2001, 78 (4), 554-555. (18) Christopher, R.H.; Middleman, S. Power-Law Flow through a Packed Tube. Ind. Eng. Chem. Fund.

1965, 4 (4), 422-426. (19) Chauveteau, G.; Kohler, N. Influence of Microgels in Polysaccharide Solutions on Their Flow Behavior through Porous Media. Soc. Pet. Eng. J. 1984, 24 (3), 361-368.

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(20) Heemsker, J.; Rosmalen, R. J.; Janssen-van, R.; Hotslag, R. J.; Teeuw, D. Quantification of Viscoelastic Effects of Polyacrylamide Solutions. Presented at the SPE/DOE Enhanced Oil Recovery Symposium, Tulsa, 15−18 April, 1984; paper SPE 12652. (21) Chauveteau, G.; Denys, K.; Zaitoun, A. New Insight on Polymer Adsorption Under High Flow Rates. Presented at the SPE/DOE Improved Oil Recovery Symposium, Tulsa, OK, 13−17 April, 2002; paper SPE 75183. (22) Seright, R. S.; Fan, T,; Wavrik, K.; Balaban, R. C. New Insights into Polymer Rheology in Porous Media. Soc. Pet. Eng. J. 2010, 16 (1), 35-42. (23) Gogarty, W. B. Mobility Control with Polymer Solutions. Soc. Pet. Eng. J. 1967, 7 (2), 161-173. (24) Dawson, R.; Lantz, R. B. Inaccessible pore volume in polymer Flooding. Soc. Pet. Eng. J. 1972, 12 (5), 448-452.

Table 1: HPAM grades and their average molecular weights HPAM Grade 3630 S 3330 S 3130 S AB 005V

Average Molecular Weight 20,000,000 8,000,000 2,000,000 500,000

Table 2: Composition and weight average molecular weights of HPAM samples HPAM Sample HPAM 1 HPAM 2 HPAM 3 HPAM 4 HPAM 5 HPAM 6 HPAM 7

Mass Fraction of HPAM Grades 3630 3330 3130 AB005 0 0 1.0 0 0.11 0.15 0.41 0.33 0.25 0.00 0.35 0.40 0.20 0.16 0.15 0.49 0 1.0 0 0 0.45 0.25 0.30 0 0.59 0.19 0.05 0.17

Avg. Molecular Weight 2.000E+06 2.008E+06 2.043E+06 2.006E+06 8.000E+06 8.000E+06 8.000E+06

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Table 3: Overall and Breakthrough recoveries for HPAM samples – Radial Coreflooding Polymer Sample HPAM-1 HPAM-2 HPAM-3 HPAM-4 HPAM-5 HPAM-6 HPAM-7

% Recovery at Cumulative Breakthrough 11.0 64.7 14.8 68.1 15.4 74.5 15.75 75.2 21.2 74.6 23.3 78.3 26.7 86.1

Table 4: Summary of results – Linear Coreflooding Polymer

K (mD)

Porosity

Pore Volume (ml)

OOIP (ml)

Swi (%)

% Secondary Recovery (water flooding)

%Tertiary Recovery (polymer + extensive water flooding)

Residual Resistance Factor

HPAM-1 HPAM-2

453.5 415.2

0.434 0.4287

42.41 41.89

35.5 34.5

0.163 0.175

47.9 51.5

32.8 34.3

1.5266 3.1248

HPAM-3

430.9

0.4307

42.09

35.0

0.169

48.0

36.0

4.5486

HPAM-4

432.1

0.4327

42.29

34.0

0.196

52.9

38.0

7.2430

10

1 HPAM 1 HPAM 2 HPAM 3 HPAM 4 HPAM 5 HPAM 6 HPAM 7

0.1

Shear Stress, Pa

Shear Viscosity, Pa.s

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 HPAM 1 HPAM 2 HPAM 3 HPAM 4 HPAM 5 HPAM 6 HPAM 7

0.1

0.01 1

10 Shear Rate, 1/s

100

1

10

100

Shear Rate, 1/s

Figure 1: Shear stress vs. Shear rate plot

Figure 2: Shear viscosity vs. Shear rate plot

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Industrial & Engineering Chemistry Research 10

10

1 1

Elastic Modulus , Pa

Viscous Modulus , Pa

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 20

HPAM 1 HPAM 2 HPAM 3 HPAM 4 HPAM 5 HPAM 6 HPAM 7

0.1

0.1 HPAM 1 HPAM 2 HPAM 3 HPAM 4 HPAM 5 HPAM 6 HPAM 7

0.01

0.001

0.01 0.01

0.1

1

10

0.01

Figure 3: Viscous modulus vs. Angular frequency plot

0.1

1

10

Angular Frequency, rad/s

Angular Frequency, rad/s

Figure 4: Elastic modulus vs. Angular frequency plot

Figure 5: Schematic diagram of the experimental setup

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Page 19 of 20 1.0 0.9 0.8

Cumulative Oil Produced, PV

0.7 0.6 0.5 0.4 HPAM 1 HPAM 2

0.3

HPAM 3 HPAM 4

0.2

HPAM 5

0.1

HPAM 6 HPAM 7

0.0 0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Polymer Solution Injected, PV Figure 6: Cumulative oil produced vs. polymer injected – Radial Coreflooding

100 90

Breakthrough Cumulative

86.1

80 70

Oil Recovery, % OOIP

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


74.5

60

75.2

78.3

74.6

68.1

64.7

50 40 30 26.7 20 10

21.2 14.8

15.4

23.3

15.75

11

0 HPAM-1

HPAM-2

HPAM-3

HPAM-4

HPAM-5

HPAM-6

HPAM-7

Figure 7: Breakthrough and Cumulative oil recovery for HPAM samples

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Page 20 of 20

Figure 8: Oil Produced at different pore volumes of polymer injected – Linear coreflooding

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On the Effect of Polymer Elasticity on Secondary and Tertiary Oil

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