Experimental Study on Hydrophobically Associating Hydroxyethyl

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Experimental Study on Hydrophobically Associating Hydroxyethyl Cellulose Flooding System for Enhanced Oil Recovery Yingrui Bai, Xiaosen Shang, Zengbao Wang, and Xiutai Zhao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01138 • Publication Date (Web): 07 May 2018 Downloaded from http://pubs.acs.org on May 7, 2018

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Experimental Study on Hydrophobically Associating Hydroxyethyl Cellulose Flooding System for Enhanced Oil Recovery Yingrui BAI, Xiaosen SHANG*, Zengbao WANG, Xiutai ZHAO School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, P.R.China

ABSTRACT A hydrophobically associating hydroxyethyl cellulose (HAHEC) used for enhanced oil recovery (EOR) was studied in the present study. The effects of HAHEC concentration, temperature, and shear rate on apparent viscosity of HAHEC solution were explored. Results show that because of the hydrophobic association of HAHEC molecules and the formation of supramolecular aggregates, the viscosifying performance of HAHEC is obviously better than that of HEC. But the apparent viscosity of HAHEC solution are sensitive to the temperature and it declines significantly especially when the temperature is less than 50℃. HAHEC solution also has satisfactory shear resistance performance and its apparent viscosity can basically return to the initial value after withdrawing severe shear action. Moreover, HAHEC shows favorable surface and interfacial activities because of the adsorption and arrangement of HAHEC molecules onto water/air surface and water/oil interface. Sand pack core experiments were conducted to investigate the enhanced oil recovery (EOR) ability of the HAHEC flooding system, results display that both the resistance factor and residual resistance factor of HAHEC solution in cores are higher than those of HEC solution. Favorable EOR performance of the HAHEC flooding is proved and high incremental oil recovery can be achieved with the application of optimized injection concentration, injection rate and injection slug size after initial water flooding. In addition, the emulsification phenomenon is obvious during the HAHEC flooding because of the favorable surface and interfacial activities of HAHEC.

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1. INTRODUCTION Water flooding is the main secondary exploitation method after the primary exploitation (natural recovery) stage during the development of oilfields, and it has presented favorable oil development performance in recent decades.1 However, because of the natural heterogeneity of reservoirs, combined with the adverse water/oil mobility ratio, the injected water easily breaks through high permeable channels and forms a fingering pattern, which can greatly lower the sweep efficiency and finally reduce the ultimate oil recovery of water flooding.2.3 Therefore, a large quantity of remaining oil still retains in the water unswept zone after water flooding.4 Moreover, because of the relatively low displacement efficiency of water, lots of residual oil also stays in pores which is already swept by water.5 Chemical flooding, especially polymer flooding, has been field tested extensively and become an effective technique for tertiary oil recovery after water flooding in mature oilfields. In China, polymer flooding has been widely applied in many oilfields, such as Daqing and Shengli oilfields.6,7 The main objective of the polymer flooding is to increase the apparent viscosity of aqueous phase, decrease the water/oil mobility ratio, in turn improve the sweep efficiency of flooding fluid, and finally enhanced oil recovery (EOR).8 The most widely applied water-soluble polymer is the partially hydrolyzed polyacrylamide (HPAM), and it has presented remarkable performance in EOR applications. Liao et al. 9 reported that by the end of 2015, the cumulative producing oil reserves achieved by polymer (HPAM) flooding was about 10×108 t and the enhanced oil recovery is about 12.5 %OOIP in PetroChina. However, with the deep development of mature oilfields and the investments in the harsh reservoirs, there are some limitations with the existing polymer flooding technology, such as the degradation (thermal, physical, bacterial, and chemical) or polymer rheological.10 As the most common used polymer, HPAM recently also suffers from severe viscosity loss mainly caused by strict temperature, high salinity and strong shear action in reservoirs.11 As is

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known that the thickening capability of HPAM mainly lies in its high molecular weight, therefore, a common and simple method used in oilfields to maintain the viscosity of polymer solution is to improve the molecular weight of HPAM.12 Lai et al.13 reported that the thickening capability of HPAM has been improved significantly with the increase of

the

molecular weight, but this method would become poor in high temperature or salinity reservoirs, and the cost would also be greatly enhanced. Lewandowska13 and Seright14 found that the HPAM demonstrates obviously shear thickening characteristics in porous media at relatively high injection rate, and the high rupture degree of long HPAM molecular chain is responsible for the aforementioned phenomenon. It also proves that the just improvement of HPAM molecular weight cannot solve the viscosity loss problem in reservoirs. To improve the adaptability of polymer flooding in harsh reservoirs, an alternative concept is to add some functional groups into the linear molecular chain of polyacrylamide.15 The application of the association between hydrophilic and hydrophobic groups that are incorporated in the same backbone of polymer molecule is the research hot spot in recent years.16 The hydrophobically associating polymers have attracted much attention in oil industry because of their unique properties, including thickening property, recoverable shear thinning property.17-19 Several different types of associating polymers, including the hydrophobically associating polyacrylamide (HAPAM) and hydroxyethyl cellulose (HAHEC), have been studied.20,21 Compared with the commonly used polymer HPAM, the hydrophobic interactions confer HAPAM interesting rheological and solution properties. At low polymer concentration (in the dilute region), the intramolecular association dominates and the hydrodynamic volume of HAPAM molecules is small, therefore the viscosity of the HAPAM solution is low. When the polymer concentration is increased, the HAPAM solution ideally moves to the semi-dilute region where the intermolecular association dominates, which leads to the network formation and substantially increases the viscosity of the solution.22,23 Liu et

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al.24 reported that the intermolecular interactions of polymeric chains provided HAPAM with high mobility control ability, and the EOR efficiency of HAPAM was 8 % higher than that of common HPAM at the same condition. Zou et al.25 presented a β-cyclodextrin functionalized HAPAM and also proved that the EOR performance of the HAPAM was obviously better than that of HPAM. However, no matter HPAM or HAPAM used for EOR, their molecular weights are very high (＞10,000 kDa), and they usually suffers from strong flow resistance and severe shear degradation in porous media. Pore space plugging often happens in low permeable formation during high molecular weight polymer flooding, which reduces the effectiveness of the polymer flooding.26 Moreover, the current demand for environmental-friendly materials is relevant also for EOR applications, and therefore a polymer with relatively low molecular weight and high thickening property may be an alternative suitable for the EOR application. The hydroxyethyl cellulose (HEC) with low molecular weight is a nonionic hydrophilic polysaccharide that has antibacterial properties and can be classified as an environmentally friendly polymer.27 Li et al.28 reported that the stability of O/W Pickering emulsion could be greatly enhanced by using a kind of regenerated HEC. To enhance the thickening property and anti-temperature/salinity property, the hydrophobically modified hydroxyethyl cellulose (HMHEC) was also synthesized by researchers.29-31 In the present study, we combined the hydrophobic association with the polymeric chain modification of HEC, and synthesized a kind of hydrophobically associating hydroxyethyl cellulose (HAHEC) used for EOR. First of all, the effects of HAHEC concentration, temperature and shear action on apparent viscosity properties of the HAHEC solution were studied; then, the surface tension and interfacial tension of HAHEC solution were explored to determine its special surface and interfacial activities; what’s more, the EOR performance of HAHEC was investigated through sand pack core experiments, and the effects of injection

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concentration, injection rate and injection slug size were measured to optimize the HAHEC flooding parameters. 2. EXPERIMENTAL SECTION 2.1. Chemicals and Fluids Hydroxyethyl cellulose (HEC, Sinopharm chemical reagent Co., Ltd, China) with a molecular weight of 370 kDa and 1-Bromododecane (Sinopharm chemical reagent Co., Ltd, China) with a purity of over 99.5 wt.% were two main chemical agents to synthesize the hydrophobically associating hydroxyethyl cellulose (HAHEC). Sodium hydrate (NaOH) was used as the activating agent; isopropyl alcohol, n-hexane and propanone were applied as the treating agent in the synthetic process. The molecular structure of HEC is shown in Figure 1a. The degassed crude oil was sampled from Shengli oilfield. The apparent viscosity of the oil was 72 mPa·s at 50℃ as measured by Brookfield DV-II+ Viscosimeter. The density of oil was 902 kg/m3. The oil was centrifuged to remove water and solids before experiments. The deionized water was applied for preparing the cellulose solution. The formation brine also sampled from Shengli oilfield was used to conduct the core flooding tests after filtration, and its compositional analysis is shown in the Table 1. 2.2. Synthesis of Hydrophobically Associating Hydroxyethyl Cellulose The brief synthesis procedure of the hydrophobically associating hydroxyethyl cellulose (HAHEC) is as follows: (a) uniformly mixing the hydroxyethyl cellulose (9.0 wt.%) with the isopropyl alcohol in a flask with three mouths; (b) dropwise adding the NaOH aqueous solution (3.0 wt.%) into the flask with rapid agitation; (c) ventilating the nitrogen gas into the flask under a sealed condition for 24 h at 25℃; (d) positioning the flask in a thermostat water bath with 80℃, and then dropwise adding the 1-Bromododecane (3.3 wt.%) into the flask; (e) ventilating the nitrogen gas again into the flask again under a sealed condition for 5 h at 80℃; (f) rapidly cooling the flask down using cool water, and taking the solid product out; 5


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(g) washing the product two times using the n-hexane, and then soaking the product using propanone for 5 h; (h) neutralizing the product to using acetic acid; (i) soaking the product using propanone again for 5 h; (j) filtrating and putting it into a oven at 45℃ for 5 h, then the target product HAHEC with a purity of 91.6 wt.% can be achieved. The molecular structure of HAHEC is shown in Figure 1b. 2.3. Apparent Viscosity Measurements In the present study, the apparent viscosity of HAHEC solution was measured with the use of a Brookfield DV-III viscometer. A sample adapter which can be sealed was installed on the viscometer, and it consisted of a cylindrical sample holder, a water jacket, a spindle and a sealing element. Calibrations of the instrument voltage and torque were done using the standard sample fluid of silicon oil. During each measurement, the HAHEC solution was poured into the sample holder, and then it was sealed and statically held for a period of time to make sure the arrival of the desired temperature. After that, the spindle was immersed into the solution at a desired shear rate and temperature. Data was automatically recorded using of processing software when the amplitude of the data variation was less than ±1.0 %. What needs to be explained is that the shear rate of the normal measurement was 7.34 s-1 except the measurement of the shear rate effect. 2.4. Surface Tension and Interfacial Tension Measurements The surface tension between HAHEC aqueous solution and air was measured using the OTB-100 optical surface tension meter and the pendant drop method to assess the surface activity of HAHEC and HEC. The experimental temperature was 30℃ (solution temperature) and the pressure condition was the atmospheric pressure. The dynamic interfacial tension (IFT) of crude oil and the aqueous solution of HAHEC was measured using the Texas-500 spinning drop tensiometer with the rotation rate of 5000 rpm at 30℃, and the minimum IFT of each sample was achieved to evaluate the interfacial 6


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activity of HAHEC and HEC. The calculation and analysis principle of the IFT measurement is shown as the equation (1). D L A = 1.2336(r w - r o )w 2 ( )3 , (1) ≥4 D n where A is the oil/water interfacial tension (mN/m); r w is the density of the water phase

(g/cm3); r o is the density of the oil phase (g/cm3); w is the rotational velocity (rpm); D is the measured drop width (mm); L is the length of oil droplet (mm); n is the refractive index of water phase. 2.5. Resistance Factor and Residual Resistance Factor Measurements The resistance factor ( FR ) and the residual resistance factor ( FRR ) were adopted to evaluate the flooding performance of HAHEC system in sand pack cores. The resistance factor reflects the capability of polymer solution to adjust the fluid flowability in core; it is equal to the ratio of the water mobility to the polymer mobility in core, and its formula is written as the equation (2):

FR =

l w kw k p / = l p mw mp

(2)

where l w and l p are the mobility of water and polymer solution; kw and k p are the water and polymer permeability (mD), mw and mp are the apparent viscosity of water and polymer solution (mPa·s). If combining the equation (2) with the Darcy formula of polymer solution, it can be changed to the equation (3): k w QL / mw Ap

FR =

(3)

where Q is the flow rate of polymer solution in core (mL/min); L is the length of core (cm); A is the cross sectional area of core (cm3); p is the pressure drop between the inlet and the oulet of core (0.1 MPa). 7


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The residual resistance factor reveals the capability of the polymer solution to lower water permeability. It can be calculated according to the equation (4) by simplifying the Darcy formula: FRR =

k w0 k w1

(4)

where k w0 and k w1 are the initial water permeability and the subsequent water permeability after the polymer treatment (mD). The experimental procedure for resistance factor and residual resistance factor measurements will be shown in the section 2.6. 2.6. Sand Pack Core Experiments Sand pack cores were prepared using a coreholder with a diameter of 1 in.(2.54 cm) and a length of 0.98 ft (30 cm). During the core packing process, the coreholder was first filled with the formation brine, and then it was vertically positioned to pack the fresh quartz sand with meshes of 60-100 in five steps. To ensure the same initial status of sand wettability and the homogeneity of the core, the coreholder was vibrated for about 5 min in each step. The procedure of flooding experiments for resistance factor and residual resistance factor measurements is as follows: (a) the sand pack core with horizontal position was vacuumed using a vacuum pump for 2 h; (b) the sand pack core was saturated with the formation brine and the initial water permeability of each core was measured; (c) the HAHEC solution with desired injection concentration or injection rate was injected into cores until the pressure drop was stable, then the resistance factor can be calculated using the equation (3) ; (d) the subsequent water flooding was performed until the pressure drop was stable, then the residual resistance factor can be calculated using the equation (4). The procedure of flooding experiments for enhanced oil recovery (EOR) is as follows: (a) the sand pack core with horizontal position was vacuumed using a vacuum pump for 2 h;

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(b) the sand pack core was saturated with the formation brine and the initial water permeability of each core was measured; (c) the sand pack core was saturated with the crude oil until the water production became negligible; (d) the sand pack core was water-flooded until the oil production became negligible; (e) the HAHEC solution were injected with desired injection concentration, injection rate or injection slug size; (f) the subsequent water flooding was conducted until the oil production became negligible again. The produced fluid was collected using a measuring cylinder to record the oil and water production. In the present study, the parameters of sand pack cores prepared for EOR and FR / FRR measurements were similar. The average water permeability was about 1000 mD, and the average porosity was about 32 V%. The average initial oil saturation of cores used for EOR experiments was about 84 IOIP%, and the average residual oil saturation after water flood was about 49 OOIP%. The experimental apparatus of EOR and FR / FRR measurements are the same, and the schematic of the apparatus is shown in Figure 2. 3. RESULTS AND DISCUSSION 3.1. Apparent Viscosity Property of HAHEC 3.1.1. Effect of Concentration Figure 3 shows the apparent viscosity variation trends of HAHEC and HEC solutions with the concentration increasing at 30℃. It can be seen that the viscosifying property of HAHEC is similar to that of hydrophobic associated polyacrylamide; that is, the apparent viscosity of HAHEC solution monotonically and sharply increases with the increase of the HAHEC concentration. When the HAHEC concentration is lower than 2000 mg/L, the maximum apparent viscosity is 91.5 mPa·s, which is higher than that of HEC solution (15.8 mPa·s) with the same concentration. For the lower concentration of HAHEC, the average distance among HAHEC molecular chains in solution is longer and the intramolecular association mode among hydrophilic and hydrophobic groups of HAHEC chains occupies the 9


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main position, leading to the tendency of the molecular chains to be curled. Therefore, the HAHEC manifests a commonplace viscosifying performance and the apparent viscosity of HAHEC solution is low. When the concentration of HAHEC is about 4000 mg/L, the apparent viscosity of the HAHEC solution sharply increases to 635 mPa·s while the apparent viscosity of HEC solution is only 61 mPa·s at the same concentration. Data reflect that the apparent viscosity of HAHEC solution is 10 times as that of HEC solution at that time. With the further increase of the HAHEC concentration, the apparent viscosity of HAHEC solution increases rapidly. When the HAHEC concentration reaches to 10000 mg/L, the apparent viscosity of HAHEC solution is 4230 mPa·s while that of HEC solution at the same concentration is only 216 mPa·s, showing a remarkable viscosifying property. What needs to be emphasized is that the concentration corresponding to the sharp increase in apparent viscosity is the critical associating concentration (CAC) of HAHEC solution. As shown in Figure 4, because of the introduction of the hydrophobic group -C12H25 into the HAHEC molecular chain, the intra or intermolecular hydrophobic association among hydrophilic and hydrophobic groups will happen in aqueous solution and the association degree is greatly affected by the HAHEC concentration. As mentioned above, the intramolecular association mode occupies the main position when the HAHEC concentration is low. After HAHEC reaches to its critical associating concentration, the main association mode among hydrophilic and hydrophobic groups in HAHEC molecular chains changes from intramolecular to intermolecular association. Then the supramolecular aggregates, a spatially cross-linked network, will be formed in aqueous solution, which significantly increases the hydrodynamic volume of HAHEC molecules and then rapidly enhance the apparent viscosity of HAHEC aqueous solution.32 To clearly explore the supramolecular aggregates formation in aqueous solution with the variation of HAHEC concentration, a series of AFM measurements under different HAHEC

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concentrations condition were conducted, the micrographs were achieved and shown in Figure 5. It shows that compared with the circumstance when the HAHEC concentration is zero, bright spots appear when the HAHEC concentration is 2000 mg/L, reflecting the initial formation of the supramolecular aggregates (Figure 5b); with the increase of the HAHEC concentration to 4000 mg/L, both the number and size of bright spots obviously grow (Figure 5c), revealing the rapidly formation of HAHEC supramolecular aggregates; with the further increase of the HAHEC concentration to 6000 mg/L, a large number of bright spots with the uniform size occupy the micrograph (Figure 5d), which reflects that the supramolecular aggregates already becomes a main occurrence state of HAHEC molecules in aqueous solution. Results are consistent with the analysis of apparent viscosity evolution, and it further proves that the viscosifying property of HAHEC has great relationship with the number and size of the supramolecular aggregates. 3.1.2. Effect of Temperature The effect of temperature from 30℃ to 90℃ on the apparent viscosity of HAHEC solution with the HAHEC concentration of 6000 mg/L was investigated, and results are shown in Figure 6. It shows that the apparent viscosity of HAHEC solution changes significantly with the variation of temperature. When the temperature is lower than 50℃, the apparent viscosity of HAHEC solution shows a rapid decline with the increase in temperature, and it decreases from 1356 mPa·s at 30℃ to 216 mPa·s at 50℃. As the temperature reaches to 50℃ or higher, the apparent viscosity of HAHEC solution slows down significantly and it is stabilized at around 89 mPa·s at 90℃. Meanwhile, the relationship between apparent viscosity and temperature of HEC solution with a concentration of 6000 mg/L was also measured. Data show that the apparent viscosity of HEC solution at 90℃ is also 7.5 mPa·s, indicating that the HAHEC solution has a better temperature resistance than that of the HEC solution. 11


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The increase in temperature has both positive and negative effects on the hydrophobic association.33 On one hand, because that the hydrophobic association among hydrophilic and hydrophobic groups is an endothermic reaction, a higher temperature is conducive to the interaction among groups and thus enhances the hydrophobic association. Meanwhile, the increase in temperature can intensify the thermal movement of hydrophobic associated polymer molecule, cause the stretching of molecular chains conducive to the increase of hydrodynamic volume, and finally enhance the apparent viscosity of the hydrophobic associated polymer solution. On the other hand, the intensified thermal movement of hydrophobic groups caused by the increase in temperature will damage the "iceberg" structure around hydrophobic groups, decrease the hydrophobic association degree, weaken the hydration degree of hydrophilic groups, and finally reduce the apparent viscosity of the hydrophobic associated polymer.34 As for HAHE, because of the relatively low molecular weight compared with that of high molecular weight polyacrylamide, the negative effect occupies the main position with the increase in temperature; namely, the intensified thermal movement and the weakened hydration degree of hydrophobic groups (-C12H25) onto HAHEC molecular chains greatly decrease the apparent viscosity of HAHEC solution. This is also the rebuilding process of the intra and intermolecular hydrophobic association structure with the temperature increasing. When the temperature is higher than 60℃, the rebuilding degree of hydrophobic association structure of HAHEC are almost completed and slightly affected by the further increase in temperature, and therefore results in a basically stable apparent viscosity. 3.1.3. Effect of Shear Rate The effect of shear action on the apparent viscosity of HAHEC solution was investigated at different temperatures with the HAHEC concentration of 6000 mg/L, and the results are shown in Figure 7. It shows that the apparent viscosity evolutions of HAHEC

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solution with the variation of shear rate in both 30℃ and 60℃ conditions are similar. With the increase of shear rate, the apparent viscosity of HAHEC solution first sharply decreases and then tends to be stable, and it can gradually increases and basically return to the initial viscosity with the decrease of the shear rate. An interesting phenomenon about the difference between apparent viscosity values under shear rate increase and decrease conditions is observed. As shown in Figure 7a, when the temperature is 30℃, with the decrease of the shear rate from 98.75 s-1 to 37.93 s-1, the apparent viscosity of HAHEC solution is slightly lower but basically the same with that of HAHEC solution under shear rate increase condition; when the shear rate decreases to the range of 37.93-18.33 s-1, the apparent viscosity is slightly higher than that of HAHEC solution under shear rate increase condition; with the further decrease of the shear rate to 18.33 s-1 or lower, the apparent viscosity is lower than that of HAHEC solution under shear rate increase condition again. Figure 7b indicates that when the temperature is 60℃, with the decrease of the shear rate from 98.75 s-1 to 30.52 s-1, the apparent viscosity is basically the same with that of HAHEC solution under shear rate increase condition; the apparent viscosity becomes higher than that of HAHEC solution under shear rate increase condition and remains this trend up to the shear rate of 7.343 s-1. Results indicate that the apparent viscosity of the HAHEC solution can basically return to its initial value with the reduction of the shear rate, and it proves the favorable shear resistance of HAHEC. The supramolecular aggregates formation in aqueous solution after the HAHEC concentration exceeds its critical associating concentration is mainly responsible for the above phenomenon. As mentioned above, the intermolecular association among hydrophilic and hydrophobic groups leads to the formation of the supramolecular aggregates, the association process is a reversible reaction, and it can be disassociated under certain circumstances.35 When the shear action is severe, the initial winding and intermolecular 13


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association structure of HAHEC molecular chains is relieved due to the strong shear stress; moreover, the degree of the intramolecular association will be improved. Therefore, the apparent viscosity of HAHEC solution is low under high shear rate condition. With the decrease of the shear rate, the supramolecular aggregates will be gradually formed because of the improvement of intermolecular association degree, which results in the gradually increase of the apparent viscosity. During the preparation of the HAHEC solution using stirring method, a low degree of intramolecular association exists because of the weak shear action. After the severe shear action, the intramolecular association structure will be relieved and the intermolecular association degree will be enhanced, and a more perfect associated and cross-linked network (supramolecular aggregates) will be rebuilt after the remove of the shear action

36,37

, as shown in Figure 8. Therefore, the apparent viscosity of the HAHEC solution

can return to its initial or even higher value. In contrast, the effect of shear action on the apparent viscosity of HEC solution was also explored at 30℃ and 60℃ with the HEC concentration of 6000 mg/L. Unlike to the apparent viscosity evolution of the HAHEC solution, the apparent viscosity of the HEC solution when the shear rate increases is the same with that when the shear rate decreases. The main reason is that the HEC molecules do not have the hydrophobic association reaction because of the lack of the long-chain hydrophobic alkyl groups; therefore, it cannot form the supramolecular aggregates in solution and shows a shear–independent viscosity property. 3.2. Surface and Interfacial Activities of HAHEC When water-soluble alkylated cellulose derivatives with long molecular chain dissolve in water, they can behave as surfactant and reduce the surface tension between solution and gas and interfacial tension between solution and oil. At present study, the surface and interfacial activities of both HAHEC and HEC solutions (6000 mg/L, 30℃) with the cellulose concentration variation were conducted, the surface tension and minimum 14


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interfacial tension (IFT) values were measured and shown in Figures 9 and 10, respectively. It can be referred that the surface tension between water and air is 71.18 mN/m at 30℃, Figure 9 shows that both HEC and HAHEC can reduce the surface tension and manifest different surface activity properties. The surface tension between HEC solution and air can be reduced to the range of 64-65 mN/m, and it remains stable with the change of HEC concentration, revealing a surface activity of concentration-independent. In contrast, the surface tension between HAHEC solution and air is obviously affected by the HAHEC concentration. When the HAHEC concentration is low (＜2000 mg/L), the surface tension is sharply reduced with the increase of HAHEC concentration, it remains at low value range (54.1-54.7 mN/m) when the HAHEC concentration is in the range of 2000-4000 mg/L. With the further increase of the HAHEC concentration, the surface tension gradually raises and finally levels off at about 55.2 mN/m, which is obviously lower than that of HEC solution (64-65 mN/m) under the same conditions. Data indicate that the surface activity of HAHEC is better than that of HEC. Figure 10 indicates that the minimum IFT evolution between HAHEC or HEC solution and crude oil with the change of cellulose concentration is similar to the surface tension evolution shown in Figure 9. The minimum IFT is reduced from 30.8 to 23.5 mN/m with the HAHEC concentration increasing from 200 to 3000 mg/L, it reaches to the lowest value (22.5 mN/m) when the HAHEC concentration is 4000 mg/L; with the further increase of HAHEC concentration, the minimum IFT rises slight and finally reaches to 23.6 mN/m when the HAHEC concentration is 7000 mg/L. Date also show that the minimum IFT between HEC solution and crude oil continuously remains at about 35.7 mN/m after the HEC concentration exceeds 2000 mg/L. Results indicate that the interfacial activity of HAHEC is also better than that of HEC. The adsorption and arrangement of HAHEC molecules onto water/air surface or 15


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water/oil interface are responsible for the surface and interfacial activities of HAHEC.38 Taking the interfacial activity as an example, because that the HAHEC molecule has hydrophilic and hydrophobic groups at the same time, it is easier to adsorb onto the water/oil interface, then the hydrophilic group (-C12H25) of HAHEC molecule will be arranged onto the interface to lower the interfacial energy of water /oil interface, and then reduce the IFT, as shown in Figure 11. The adsorptive capacity of HAHEC molecules onto the interface greatly affects its interfacial activity. When the HAHEC concentration is low, the adsorptive capacity of HAHEC molecules onto the water/oil interface is small, but the initial adsorbed HAHEC molecules can significantly reduce the IFT compare with the missing of HAHEC molecules. With the increase of the HAHEC concentration, the adsorptive capacity of HAHEC molecules onto the interface gradually increases and the IFT is further reduced correspondingly. The adsorptive capacity of HAHEC molecules will reach to a saturated state after the HAHEC concentration exceeds a certain value, and the minimum IFT between water and oil will be achieved at that time. The above explanation also applies to the change trend of surface tension between HAHEC solution and air. Data in Figures 9 and 10 also reveal that the surface and interfacial activities of HAHEC are related with the critical associating concentration of HAHEC in solution. It is because that when the HAHEC concentration exceeds its critical associating concentration (2000 mg/L), the apparent viscosity of HAHEC solution begins to sharply increase due to the hydrophobic association among hydrophilic and hydrophobic groups of HAHEC molecules, then it will limit the movement of HAHEC molecules towards the water/air surface or water/oil interface; even some already adsorbed HAHEC molecules begin to associate with each other to form the molecular aggregate, which will destroy the initial oriented arrangement of HAHEC molecules and then correspondingly slow down the decreasing rates of both surface tension and IFT.

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3.3. Enhanced Oil Recovery Performance of HAHEC Flooding 3.3.1. Effect of Injection Concentration The effects of the injection concentration on the resistance factor and residual resistance factor of HAHEC and HEC in porous media were studied with HAHEC or HEC injection rate of 0.5 mL/min and with the temperature of 60℃. Figure 12a indicates that the resistance factor of HAHEC solution shows a continuously increasing trend with the increase of the injection concentration, but the increment rate of the resistance factor is different. In contrast, the resistance factor of HEC solution shows a slow but gradually growth trend. When the HAHEC concentration is low and increases from 200 to 2000 mg/L, the resistance factor of HAHEC is improves from 10 to 24, although it is higher than that of HEC, there is no obvious different between the resistance factor of HAHEC and that of HEC. After the HAHEC concentration exceeds 2000 mg/L, the resistance factor increases significantly with the improvement of the injection concentration and reaches to 374 when the HAHEC concentration is 10000 mg/L, which is about 10 times higher than that of HEC (38) with a same concentration. Figure 12a show that the change trend of resistance factor of HAHEC solution in porous media is similar with that of the apparent viscosity with the variation of the HAHEC concentration. The main reason is that the resistance factor is greatly affected by the apparent viscosity of the injected polymer solution, and the apparent viscosity is significantly influenced by the hydrophobic association reaction for the HAHEC solution. Therefore, when the HAHEC concentration is low, the intramolecular association mode occupies the main position, which leads to low apparent viscosity and small resistance factor. After the HAHEC reaches to its critical associating concentration (about 2000 mg/L), the main association mode among hydrophilic and hydrophobic groups in HAHEC molecules changes to the intermolecular association, and the apparent viscosity of HAHEC solution will be greatly

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enhanced, resulting in high resistance factor of HAHEC solution. Figure 12b reflects that the change trends of residual resistance factors of HAHEC and HEC are similar with those of resistance factors. In addition to the effect of apparent viscosity, the adsorption capacity of HAHEC molecules onto the pore surface greatly affects the residual resistance factor. Generally speaking, a high residual resistance factor is always accompanied by a large adsorption capacity of HAHEC molecules, and the adsorption capacity rises as the HAHEC concentration increasing. Therefore, the residual resistance factor of HAHEC shows a continuously increasing trend with the increase of the HAHEC concentration. The enhanced oil recovery performances of the HAHEC and HEC solutions with different injection concentrations were investigated using sand pack cores (60℃), and the incremental oil recovery results are shown in Figure 13. It shows that the incremental oil recovery increases slightly from 7.6 to 8.4 %OOIP when the HAHEC concentration rises from 500 to 1000 mg/L, but it sharply increases to 15.9 %OOIP as the HAHEC concentration is enhanced to 2000 mg/L; with the further increase of the HAHEC concentration to 6000 mg/L, the incremental oil recovery continuously rises to 24.5 %OOIP; after that, the incremental oil recovery slightly increases and finally levels off at about 25.8 %OOIP when the HAHEC concentration is enhanced to 10000 mg/L. In contrast, the incremental oil recovery always keeps a slight rising trend with the HEC concentration increases, but data reveals that the enhanced oil recovery performance of HEC is obviously lower than that of the HAHEC. Figure 13 also indicates that when the HAHEC concentration increases from 500 to 6000 mg/L, the increasing trend of the incremental oil recovery is similar with that of the resistance factor of HAHEC solution in porous media, as shown in Figure 12a. Because of the increase in resistance factor (or apparent viscosity) of HAHEC solution, the water-oil mobility ratio will be reduced with the increase of HAHEC concentration, and more flooding

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fluid can be diverted into small pores without being flooded previously, which will contribute to the enhancement of the conformance efficiency and finally enhance the oil recovery. Moreover, the improvement of the viscoelasticity of HAHEC solution caused by the supermolecular aggregates formation will benefit for the enhancement of the displacement efficiency, which also can enhance the oil recovery. It manifests that there is an optimum injected HAHEC concentration (6000 mg/L in the present study) to achieve almost the best EOR performance in porous media for HAHEC flooding. 3.3.2. Effect of Injection Rate The effects of the injection rate on the resistance factor and residual resistance factor of HAHEC and HEC in porous media were explored with the HAHEC or HEC concentration of 6000 mg/L (60℃), and results are shown in Figure 14. Data in Figure 14a indicate that the resistance factor curve can be divided into three segments. Segment a: when the injection rate of HAHEC solution is lower than 1.0 mL/min, the resistance factor shows a sharp decreasing trend with the injection rate increasing from 0.2 to 1.0 mL/min. Segment b: the resistance factor rises slightly with the injection rate increasing from 1.0 to 1.5 mL/min. Segment c: the resistance factor of HAHEC gradually decreases with a further increase of the injection rate. The shear stress and tensile stress forced on HAHEC molecules in porous media are responsible for the resistance factor evolution of HAHEC solution. When the injection rate is low, the shear flow of HAHEC solution occupies the main position in porous media, then the shear stress forced on HAHEC molecules is relatively strong but the tensile stress is weak. At that time, the disassociation reaction among hydrophilic and hydrophobic groups will be severe and the supermolecular aggregates of HAHEC molecules will be destroyed in a large scale, leading to the apparent viscosity reduction of the HAHEC solution in porous media, which further results in the resistance factor decrease of HAHEC solution. The tensile stress forced on HAHEC molecules will gradually increase with the injection rate improving, and

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the resistance factor will be reduced to the minimum value when the shear stress and tensile stress are balanced. Moreover, the elasticity property of HAHEC molecules (supermolecular aggregates) is gradually revealed with the increase of the tensile stress, which will enhance the flow resistance of HAHEC solution in pore throat and then contributes to the increase of the resistance factor. When the injection rate is high enough, the tensile stress forced on the HAHEC supermolecular aggregates is strong correspondingly, which can break the aggregates structure up, reduce the association degree and then result in the decrease of the resistance factor. Figure 14b shows that the evolution of residual resistance factor of HAHEC solution with the injection rate variation in porous media is different from that of the resistance factor. The residual resistance factor raises form 32 to 40 when the injection rate increase from 0.2 to 0.5 mL/min, and it continuously declines with the injection rate further increasing. The main reason for this phenomenon is that when the injection rate is relatively low, some HAHEC molecules will be freed from the supermolecular aggregates because of the disassociation reaction among hydrophilic and hydrophobic groups of HAHEC molecules, and then the adsorption capacity of HAHEC molecules onto the pore surface will be improved, which contributes to the increase of the residual resistance factor. When the injection rate exceeds a certain value (0.5 mL/min in present study), although a higher amount of HAHEC molecules will be freed, the adsorption capacity of HAHEC molecules will instead decrease because of the strong washing action and the contact time reduction between freed HAHEC molecules and pore surfaces, which will results in the decline of the residual resistance factor of HAHEC solution. In contrast, both the resistance factor and residual resistance factor of HEC solution are insensitive to the change of the injection rate; moreover, they are obviously lower than that of HAHEC solution. The main reason is that there are no hydrophobic association and

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supermolecular aggregates in HEC solution, the apparent viscosity of HEC solution is low and the elasticity property of HEC solution is weak, therefore both shear stress and tensile stress have small effects on the solution viscosity, resulting that the HEC solution shows a “injection rate-independent” presentation. Figure 15 illustrates the effect of the injection rate which increases from 0.2 mL/min to 3.0 mL/min on the incremental oil recovery after water flooding, and both the injected chemical slug sizes of HAHEC and HEC are 0.80 PV. It shows that when the injection rate is 0.2 mL/min, the incremental oil recovery of HAHEC is 22.3 %OOIP; with the increase of the injection rate from 0.2 to 0.5 mL/min, the incremental oil recovery is correspondingly enhanced to 22.3 %OOIP; with the further increase of the injection rate to 3.0 mL/min, the incremental oil recovery of HAHEC levels off to about 17.3 %OOIP. The evolution of the incremental oil recovery of HEC is different with that of HAHEC, when the injection rate increases from 0.2 to 0.5 mL/min, it is similar with that of HAHEC and shows a rising trend, and the highest incremental oil recovery data is 10.3 %OOIP; with the injection rate further increasing to 3.0 mL/min, the incremental oil recovery of HEC continuously declines to 6.0 %OOIP. Data show that the EOR effectiveness of HEC is not a patch on that of HAHEC, and it also indicate that a proper injection rate is important for the HAHEC flooding system to achieve a satisfactory oil recovery. According to the contrastive analysis of the resistance factor/residual resistance factor and the incremental oil recovery, the highest incremental oil recovery of HAHEC does not match with its highest resistance factor but go well with the highest residual resistance factor. The reason is that when the injection rate is low (0.2, 0.5mL/min), the disassociation of the HAHEC supramolecular aggregation caused by the shear action in porous media sets lots of HAHEC molecules free, then more HAHEC molecules can absorb onto the sand surface and oil/water contact to make the oil easily being stripped and displaced, which results in a

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relatively high incremental oil recovery. With the increase of the injection rate, the fingering phenomenon becomes easier to happen which leads to a weak sweep efficiency of the HAHEC solution and a low oil recovery. When the injection rate is high, the elastic property of the HAHEC solution under that condition plays an important role to maintain the resistance factor, and thus guarantees the stabilization of the incremental oil recovery.39 In contrast, because the HEC solution lacks the elastic property under high injection rate condition, it will be thinned under shear action and thus weaken the sweep efficiency. 3.3.3. Effect of Injection Slug Size The injection slug size is one of major considerations during the design of chemical flooding system because of the economic fact. The aim of the injection slug size investigation is to optimize a small but appropriate slug size which can achieve satisfactory incremental oil recovery. In the present study, six sand pack flooding experiments were conducted using the HAHEC flooding system (6000 mg/L, 0.5 mL/min, 60℃) while increasing the injection slug size from 0.2 to 1.2 PV after the initial water flooding process, and results are shown in Figure 16. According to the data analysis of the incremental oil recovery with the injection slug size changing in Figure 16, the range of the slug size can be divided into three sections. Section a: when the injected HAHEC slug size is enhanced from 0.2 PV to 0.6 PV, the residual oil which still remains in cores after initial water flooding is markedly extracted by the HAHEC flooding system, the incremental oil recovery shows an almost linear growth and increases from 8.1 %OOIP to 20.1 %OOIP. Section b: with the injection slug size of HAHEC solution increasing from 0.6 PV to 0.8 PV, although the incremental oil recovery keeps rising from 20.1 %OOIP to 23.9 %OOIP, the increment slows down compared with that in the section a. Section c: with the HAHEC slug size further increasing to 1.2 PV, the incremental oil recovery slowly increases and finally reaches 25.3 %OOIP. In contrast, the incremental oil

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recovery of HEC flooding system is obviously lower than that of HAHEC flooding system with the same injection slug size. Results indicate that a higher incremental oil recovery is always companied by a larger injection slug size, but the 0.80 PV is an optimal injection size when the incremental oil recovery and the expense are both taken into consideration. Another phenomenon is that the turbid produced fluids were sampled during the HAHEC and HEC flooding process, and its micrographs were shown in Figure 17. It can be observed that the emulsified oil droplets in the produced fluid are responsible for the “turbid” phenomenon. In contrast, the emulsified oil droplets density in Figure 17a is greatly higher than that in Figure 17b. It proves that more emulsified oil droplets are generated during the HAHEC flooding, and the favorable surface and interfacial activities of HAHEC accounts for the emulsification phenomenon. Just as the discussion in the section 3.2, the surface tension and IFT can be reduced because of the adsorption and arrangement of HAHEC molecules onto water/air surface and water/oil interface, which contributes to the emulsification of oil in water, part of the incremental oil is extracted out in the form of emulsified oil droplets or emulsion during the HAHEC flooding. To visually explore the microscopic flooding phenomenon of the HAHEC system, the glass-etched micromodel tests were carried out; the intrusion phenomenon and the entrainment phenomenon of HAHEC flooding system for oil phase were observed and shown in Figures 18 and 19, respectively. The oil/water interfacial film is initially rigid because of the existence of the gum asphaltic, the adsorption of HAHEC molecules onto the oil/water interface can replace some gum asphaltic molecules and make the rigid film soft; therefore, the displacement front of HAHEC system easily intrudes into the oil phase under the driving force of subsequent fluid and shows the intrusion phenomenon, as shown in Figure 18a. At that moment, the oil in and around the intruded area suffered high shear stress and is easily emulsified to form emulsified oil droplets (Figure 18b). With the gradually expansion of the

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intruded area, more oil will be emulsified and produced in the form of emulsified oil droplets (Figures 18c and 18d). A reason for the entrainment phenomenon is also closely related to the adsorption of HAHEC molecules onto the pore surface. The adhesive force between oil phase and pore surface is usually high if the pore surface is oil-wet, lots of the residual oil remains onto the pore surface although the oil in the pore center can be easily flooded forward.40 During the HAHEC flooding, the adsorption of HAHEC molecules can convert the part of pore surface from oil-wet to water-wet to reduce the adhesive force, and then the adherent oil will be flooded forward along the surface (Figure 19).41 To more clearly prove that the adsorption of HAHEC molecules can alter the wettability of pore surface, the wetting angle of oil-wet slabbed core of sandstone which were soaked in the HAHEC solution (2000 mg/L) for 24 h was measured, and it decreased form to 112° to 76°. Moreover, the adherent oil can also be entrained by the HAHEC flooding system due to the viscoelasticity of HAHEC solution. The above reasons results in the entrainment phenomenon during the HAHEC flooding and finally contributes to the enhancement of residual oil recovery. 4. CONCLUSIONS A hydrophobically associating hydroxyethyl cellulose (HAHEC) was synthesized and its apparent viscosity property, surface activity, interfacial activity, and enhanced oil recovery performance were investigated. Results of the present study are as follows: (1) The thickening or viscosifying property of HAHEC is obviously better than that of HEC after its concentration exceeds its critical associating concentration (CAC), and the intermolecular association of HAHEC molecules which contributes to the formation of the supramolecular aggregates is responsible for this phenomenon. (2) The apparent viscosity of HAHEC solution are sensitive to the temperature and it declines significantly especially when the temperature is lower than 50℃. Moreover, HAHEC has satisfactory shear resistance performance and the apparent viscosity of HAHEC

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solution can basically return to the initial state after severe shear action. (3) HAHEC can sharply reduce the surface tension of solution/air and the interfacial tension of solution/oil to lower value after its concentration is higher than the CAC compared with that of HEC, and it is conducive to enhance oil recovery during the HAHEC flooding. (4) Both the resistance factor and residual resistance factor of HAHEC solution in cores are higher than those of HEC solution, and they are related with the injection concentration and injection rate of HAHEC solution. (5) The EOR performance of the HAHEC flooding in porous media is favorable, and high incremental oil recovery can be achieved after initial water flooding with the optimizations of injection concentration, injection rate and injection slug size. Moreover, the incremental oil is produced in the form of emulsified oil droplets during the HAHEC flooding, and the favorable surface and interfacial activities of HAHEC accounts for the emulsification phenomenon. CORRESPONDING AUTHOR INFORMATION Corresponding authors Name: Xiaosen SHANG; Telephone: +86 18562567190; Fax: 86-532-86981172; E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This research is financially supported by National Natural Science Foundation of China (Grant 51704310), China Postdoctoral Science Foundation Funded Project (Grant 2017M610456, 2016M602226), Natural Science Foundation of Shandong Province, China (Grant ZR2017BEE034), PetroChina Innovation Foundation (Grant 2017D-5007-0203), Fundamental Research Funds for the Central Universities (Grant 18CX02159A,

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18CX02163A), and Qingdao Postdoctoral Applied Research Project (Grant 2016221). REFERENCES [1] Zhang, P.; Wang, Y.F.; Chen, W.H.; Yu, H.Y.; Qi, Z.Y.; Li, K.Y. Preparation and solution characteristics of a novel hydrophobically associating terpolymer for enhanced oil recovery. J. Solution Chem. 2011, 40, 447−457. [2] Olajire, A.A. Review of ASP EOR technology in the petroleum industry: Prospects and challenges. Energy 2014, 77, 963−982. [3] Yan, L.; Cui, Z.; Song, B.; Pei, X.; Jiang, J. Dioctyl glyceryl ether ethoxylates as surfactants for surfactant−polymer flooding. Energ. Fuel 2016, 30, 5425−5431. [4] Barnaji, M,J,; Pourafshary, P; Rasaie, M,R. Visual investigation of the effects of clay minerals on enhancement of oil recovery by low salinity water flooding. Fuel 2016, 184, 826−835. [5] Bai, Y.R.; Xiong, C.M.; Wei, F.L.; Li, J.J.; Shu, Y.; Liu, D.X. Effects of fracture and matrix on propagation behavior and water shut-off performance of a polymer gel. Energ. Fuel 2015, 29, 447−458. [6] Le, J. J.; Wu, X. L.; Wang, R.; Zhang, J. Y.; Bai, L. L.; Hou, Z. W. Progress in pilot testing of microbial-enhanced oil recovery in the Daqing oilfield of north China. Int. Biodeter. Biodegr. 2015, 97,188−194. [7] Cao, Y.B.; Liu, D.Q.; Zhang, Z.P.; Wang, S.T.; Wang, Q.; Xia, D.H. Steam channeling control in the steam flooding of super heavy oil reservoirs-Shengli oilfield. Petrol. Explor. Develop. 2012, 39, 785−790. [8] El-hoshoudy, A.N.; Desouky, S.E.M.; Al-Sabagh, A.M.; Betiha, M.A.; El-kady, M.Y.; Mahmoud, S. Evaluation of solution and rheological properties for hydrophobically associated polyacrylamide copolymer as a promised enhanced oil recovery candidate. Egyptian J. Petrol. 2017, 26, 779–785.

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[9] Liao, G.Z.; Wang,Q.; Wang, H.Z.; Liu, W.D. Chemical flooding development status and prospect. Acta Petrolei Sinica 2017, 38, 196−207. [10] Abidina, A.Z.; Puspasaria,T.; Nugroho, W.A. Polymers for enhanced oil recovery technology. Procedia Chem. 2012, 4, 11–16. [11] Hu, S. S.; Zhang, L.; Cao, X. L.; Guo, L. L.; Zhu, Y. W.; Zhang, L.; Zhao, S. Influence of crude oil components on interfacial dilational properties of hydrophobically modified polyacrylamide. Energ. Fuel 2015, 29, 1564−1573. [12] Choi, J.; Ka, D.; Chung, T.; Jung, J.; Koo, G.; Uhm, T.; Jung, S. H.; Park, S.; Jung, H. T. Evaluation of highly stable ultrahighmolecular-weight partially hydrolyzed polyacrylamide for enhanced oil recovery. Macromol. Res. 2015, 23, 518−524. [13] Lewandowska, K. Comparative studies of rheological properties of polyacrylamide and partially hydrolyzed polyacrylamide solutions. J. Appl. Polym. Sci. 2007, 103, 2235–2241. [14] Seright, R.S.; Seheult, M.; Talashek, T. Injectivity characteristics of EOR polymers. SPE Reserv. Eval. Eng. 2009, 12, 783–792. [15] Lai, N.J.; Zhang, Y.; Zeng, F.H.; Wu, T.; Zhou, N.; Xu, Q.; Ye, Z.B. Effect of degree of branching on the mechanism of hyperbranched polymer to establish the residual resistance factor in high permeability porous media. Energ. Fuel 2016, 30, 5576−5584. [16] Wever, D.A.Z.; Picchioni, F.; Broekhuis, A.A. Polymers for enhanced oil recovery: A paradigm for structure–property relationship in aqueous solution. Prog. Polym. Sci. 2011, 36, 1558–1628. [17] Feng, Y.J.; Billon, L.; Grassl, B.; Bastiat, G.; Borisov, O.; Francois, J. Hydrophobically associating polyacrylamides and their partially hydrolyzed derivatives prepared by post-modification. 2. Properties of non-hydrolyzed polymers in pure water and brine. Polymer 2005, 46 , 9283–9295. [18] Zhao, Y.Z.; Zhou, J.Z.; Xu, X.H.; Liu, W.B.; Zhang, J.Y.; Fan, M.H.; Wang, J.B.

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Synthesis and characterization of a series of modified polyacrylamide. Colloid Polym. Sci. 2009, 287, 237–241. [19] Jiang, T.T.; Lu, J.; Wang, H.Y.; Wang, B.H.; Han, H.J.; Wu, H.J. Analysis on toxic and hazardous substances of polymer surfactants used in oilfields. Adv. Mater. Res. 2013, 805, 1344–1347. [20] Jiang, G. Q.; Liu, F. Q. Effect of mineral salts on steady rheological properties of nonionic hydrophobically modified polyacrylamide and its stress-relaxation behavior. J. Macromol. Sci., Part A: Pure Appl.Chem. 2013, 50, 1209−1217. [21] Taylor, K.C.; Nasr-El-Din, H.A. Water-soluble hydrophobically associating polymers for improved oil recovery: a literature review. J. Pet. Sci. Eng. 1998, 19, 265–280. [22] Feng Y, Billon L, Grassl B, Khoukh A, Franc¸ois J. Hydrophobically associating polyacrylamides and their partially hydrolyzed derivatives prepared by post modification 1: Synthesis and characterization. Polymer 2002, 43, 2055–2064. [23] Lara-Ceniceros, A.C.; Rivera-Vallejo, C.; Jimenez-Regalado, E.J. Synthesis, characterization and rheological properties of three different associative polymers obtained by micellar polymerization. Polym. Bull. 2007, 58, 425–33. [24] Liu, R.; Pu, W.F.; Sheng, J.J.; Du, D.J. Star-like hydrophobically associative polyacrylamide for enhanced oil recovery: comprehensive properties in harsh reservoir conditions. J. Taiwan Inst. Chem. E. 2017, 80, 639–649. [25] Zou, C.J.; Zhao, P.W.; Hu, X.Z.; Yan, X.L.; Zhang, Y.Y.; Wang, X.J.; Song, R.T.; Luo, P.Y. β-cyclodextrin-functionalized hydrophobically associating acrylamide copolymer for enhanced oil recovery. Energ. Fuel 2013, 27, 2827−2834. [26] Sabhapondit, A., Borthakur, A., Haque, I. Water Soluble acrylamidomethyl propane sulfonate (AMPS) copolymer as an enhanced oil recovery chemical. Energ. Fuel 2003, 17, 683–688.

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Energy & Fuels 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

[27] Kjøniksen, A.L.; Beheshti, N.; Kotlar, H. K.; Zhu, K.Z.; Nystrom, B. Modified polysaccharides for use in enhanced oil recovery applications. Eur. Polym. J. 2008, 44, 959– 967. [28] Li, Z.; Wu, H.R.; Yang, M.; Xu, D.R.; Chen, J.; Feng, H.S. Stability mechanism of O/W Pickering emulsions stabilized with regenerated cellulose. Carbohyd. Polym. 2018, 181, 224– 233. [29] Kjoniksen AL, Beheshti N, Kotlar HK, Zhu KZ, Nystrom B. Modified polysaccharides for use in enhanced oil recovery applications. Eur. Polym. J. 2008, 44, 959–967. [30] Kawakami K, Ihara T, Nishioka T, Kitsuki T, Suzuki Y. Salt tolerance of an aqueous solution of a novel amphiphilic polysaccharide derivative. Langmuir 2006, 22, 3337–3343. [31] Zhao GQ, Chen SB. Nonlinear rheology of aqueous solutions of hydrophobically modified hydroxyethyl cellulose with nonionic surfactant. J. Colloid Interf. Sci. 2007, 316, 858–866. [32] Yang, Z.L.; Gao, Y.B.; Li, C.X.; Yue, Q.Y.; Liu, B. Synthesis and characterization of hydrophobically associating cationic polyacrylamide. Chem. Eng. J. 2010, 161, 27–33. [33] Badiger MV, Lutz A, Wolf BA. Interrelation between the thermodynamic and viscometric behaviour of aqueous solutions of hydrophobically modified ethyl hydroxyethyl cellulose. Polymer 2000, 41, 1377–1384. [34] Gong, H.J.; Zhang, H.; Xu, L.; Li, K.N.; Yu, L.; Sang, Q.; Li, Y.J. The synergistic effect of branched preformed particle gel and hydrolyzed polyacrylamide on further enhanced oil recovery after polymer flooding. Energ. Fuel 2017, 31, 7904−7910. [35] Liu, J.X.; Lu, X.G.; Liu, J.F.; Hu, S.Q.; Xue, B.Q. Mechanism and gelling effects of linked polymer solution in the core. Petrol. Explor. Dev. 2013, 40, 474−480. [36] Zhao GQ, Khin CC, Chen SB, Chen BH. Nonionic surfactant and temperature effects on the viscosity of hydrophobically modified hydroxyethyl cellulose solutions. J. Phys. Chem. B

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2005, 109, 14198–14204. [37] Song, Z.; Liu, L.; Wei, M.; Bai, B.; Hou, J.; Li, Z.; Hu, Y. Effect of polymer on disproportionate permeability reduction to gas and water for fractured shales. Fuel 2015, 143, 28–37. [38] Li Q, Ye L, Cai Y, Huang RH. Study of rheological behavior of hydrophobically modified hydroxyethyl cellulose. J. Appl. Polym. Sci. 2006, 100, 3346–3352. [39] Wei, B.; Li, H.; Li, Q.Z.; Lu, L.M.; Pu, W.F.; Wen, Y.B. Investigation of synergism between surface-grafted nano-cellulose and surfactants in stabilized foam injection process. Fuel 2018, 211, 223–232. [40] Wei, B.; Li, Q.Z.; Jin, F.Y.; Li, H.; Wang, C.Y. The potential of a novel nano-fluid in enhancing oil recovery. Energ. Fuel 2016, 30, 2882–2891. [41] Hu, S.S.; Zhang, L.; Cao, X.L.; Guo, L.L.; Zhu, Y.W.; Zhang, L.; Zhao, S. Influence of crude oil components on interfacial dilational properties of hydrophobically modified polyacrylamide. Energ. Fuel 2015, 29, 1564–1573.

FIGURES H

OH

CH2OCH2CH2OH

OH

H

H

O

H

H

H O

H

O

OH

H

H

OH

O

CH2OCH2CH2OH

(a) HEC

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H

Energy & Fuels

H

OH

CH2OCH2CH2OR O

OH

H

H

H

H O

H

H

O

OH

H

H

OH

H

O CH2OCH2CH2OH

(b) HAHEC Figure 1 Schematic of HEC and HAHEC molecular structures. R represents the hydrophobic group (-C12H25).

Figure 2 Schematic of the experimental apparatus for EOR and FR/FRR measurements. 5000 4500 Apparent viscosity, mPa.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

Page 32 of 42

HAHEC HEC

4000 3500 3000 2500 2000 1500 1000 500 0 0

2000 4000 6000 8000 Cellulose concentration, mg/L

10000

Figure 3 Relationship between apparent viscosity and concentration of HAHEC and 31


Page 33 of 42 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

Energy & Fuels

HEC.

(a)

(b)

Figure 4 Schematic of hydrophobic association. (a) intramolecular association; (b) intermolecular association.

(a)

(b)

(c)

(d)

Figure 5 AFM micrographs of supramolecular aggregates with different HAHEC

32


Energy & Fuels

concentrations in aqueous solution. (a) 0 mg/L; (b) 2000 mg/L; (c) 4000 mg/L; (d) 6000 mg/L. 1600 Apparent viscosity, mPa.s

1400 1200 1000 800 600 400 200 0 30

40

50 60 70 Temperature, ℃

80

90

Figure 6 Relationship between temperature and apparent viscosity of HAHEC solution (HAHEC 6000 mg/L). 1400 30℃

1200 Apparent viscosity, mPa.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

Page 34 of 42

1000

Increase of shear rate Decrease of shear rate 600 500

800

400

600

300 200

400

100 15

20

25

30

35

40

200 0 0

10

20

30

40 50 60 70 -1 Shear rate, s

80

(a)

33


90 100

Page 35 of 42

180 Increase of shear rate Decrease of shear rate


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

Energy & Fuels

140

60℃

120 100 80 60 40 20 0

0

10

20

30

40 50 60 70 -1 Shear rate, s

80

90 100

(b) Figure 7 Apparent viscosity evolution of HAHEC solution with the variation of shear rate (HAHEC 6000 mg/L).

(a)

(b)

(c)

Figure 8 Schematic of the rebuilding process of the associated and cross-linked network after shear action.

34


Energy & Fuels

66

Apparent viscosity, mPa.s

3000 2500

64

HEC

62

2000 1500

60

HAHEC

58

1000

56 500 HAHEC

Surface tension, mN/m

54

0 0

1000

2000 3000 4000 5000 6000 Cellulose concentration, mg/L

7000

52

Figure 9 Surface activities of HAHEC and HEC solutions with the cellulose concentration variation. 40


38 2500

HEC

36 34

2000

32 1500

HAHEC

30 28

1000

26 500

Minimum IFT, mN/m

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 36 of 42

24

HAHEC

22

0 0

1000

2000 3000 4000 5000 6000 Cellulose concentration, mg/L

7000

20

Figure 10 Interfacial activities of HAHEC and HEC solutions with the cellulose concentration variation.

35


Page 37 of 42

Figure 11 Schematic of adsorption and oriented arrangement of HAHEC molecules onto water/oil interface. 300 270

HAHEC HEC

240 Resistance factor

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

Energy & Fuels

210 180 150 120 90 60 30 0

0

2000 4000 6000 8000 Injection concentration, mL/min

(a)

36


10000

Energy & Fuels

100

Residual resistance factor

90

HAHEC HEC

80 70 60 50 40 30 20 10 0

0

2000

4000 6000 8000 Injection concentration, mg/L

10000

(b) Figure 12 Resistance factor evolutions with injection concentration variation of HAHEC and HEC solutions in porous media (both HAHEC and HEC injection rates are 0.5 mL/min). (a) resistance factor evolution; (b) residual resistance factor evolution. 30 Incremental 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

Page 38 of 42

27

HAHEC

24

HEC

21 18 15 12 9 6 3 0

500

1000

2000 4000 6000 8000 Injection concentration, mg/L

10000

Figure 13 Incremental oil recovery evolution with injection concentration variation of HAHEC and HEC solutions in porous media (both HAHEC and HEC injection rates are 0.5 mL/min).

37


Page 39 of 42

200 180

Resistance factor

160

segment b

140 120

HAHEC HEC segment c

segment a

100 80 60 40 20 0 0.0

0.5

1.0 1.5 2.0 Injection rate, mL/min

2.5

3.0

(a) 50 HAHEC HEC

45 Residual resistance factor

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

Energy & Fuels

40 35 30 25 20 15 10 5 0 0.0

0.5


2.5

3.0

(b) Figure 14 Resistance factor and residual resistance factor evolutions with injection rate variation of HAHEC and HEC solutions in porous media (both HAHEC and HEC concentrations are 6000 mg/L). (a) resistance factor evolution; (b) residual resistance factor evolution.

38


Energy & Fuels

Incremental oil recovery,% OOIP

27 24

HAHEC

21

HEC

18 15 12 9 6 3 0

0.2

0.5

2.5


3.0

Figure 15 Incremental oil recovery evolution with injection rate variation of HAHEC and HEC solutions in porous media (both HAHEC and HEC concentrations are 6000 mg/L). 30 27 Incremental 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

Page 40 of 42

section a

section b

section c

24 21

HAHEC

18

HEC

15 12 9 6 3 0

0.2

0.4

0.6 0.8 1.0 Injection slug size, PV

1.2

Figure 16 Incremental oil recovery evolution with injection slug size variation of HAHEC and HEC solutions in porous media (both HAHEC and HEC concentrations and injection rates are 6000 mg/L and 0.5 mL/min).

39


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Energy & Fuels

(a)

(b)

Figure 17 Micrographs of emulsified oil droplets in produced fluid. (a) HAHEC flooding; (b) HEC flooding.

(a)

(b)

(c)

(d)

Figure 18 Intrusion phenomenon of HAHEC flooding front into oil phase.

40


Energy & Fuels 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 42 of 42

(a)

(b)

(c)

(d)

Figure 19 Entrainment phenomenon of HAHEC flooding system for oil phase.

TABLES Table 1 Analysis of the formation brine sample. Ions

K+ + Na+

Ca2+

Mg2+

CO32-

HCO3-

SO42-

Cl-

Concentration (mg/L)

6756

205

75

63

298

75

7824

Total salinity (mg/L)

15296

41


Experimental Study on Hydrophobically Associating Hydroxyethyl

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