Novel Evaluation Method of Foam Agents for Thermal Recovery in

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A Novel Evaluation Method of Foam Agents for Thermal Recovery in Heavy Oil Reservoirs Zhanxi Pang, Yalong Wu, and Meng Zhao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00455 • Publication Date (Web): 01 Apr 2016 Downloaded from http://pubs.acs.org on April 2, 2016

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A Novel Evaluation Method of Foam Agents for Thermal Recovery in Heavy Oil Reservoirs Zhanxi Pang a,*, Yalong Wu, Meng Zhao a

MOE Key Laboratory of Petroleum Engineering, China University of Petroleum, Beijing 102249, China

ABATRACT: Aiming at the influence of temperature on foaming ability and blocking characteristics during steam injection, a study is carried out to establish a new evaluation method of foaming agent at variable temperatures in heavy oil reservoir. The method synthetically considers the influence of temperature variation on foaming ability, foam stability and resistance factor by introducing some important parameters, such as the average foam comprehensive index, the average foam resistance factor, the weighted factor, the comprehensive value of foam performance. In laboratory, five foaming agents are quantificationally evaluated according to the method introduced in this article. The experimental results indicates that the agent A, ZWF-1, is the optimum foaming agent in terms of the order of the dimensionless evaluation parameters. Aiming at an actual well-group of an oilfield from China, the pilot test of foam profile control is implemented. The practice results show that the cumulative incremental oil production reaches 675.9 m3 within three and a half months and the injection pressure largely increases after foam injection during steam flooding.

KEYWORDS: Heavy oil reservoir; Thermal recovery; Foaming agent; Evaluation method; Physical simulation

1. INTRODUCTION Steam injection, which accounts for more than 80% of annual heavy oil production in the world, is being developed as one of the major recovery technologies for heavy oil reservoirs.1,2 However, due to the low viscosity and high mobility of steam, steam override and breakthrough exist widely in the application of steam injection for heavy oil reservoirs, which leads to reduction of steam sweep volume. Moreover, reservoir heterogeneity will make steam breakthrough worse in general.3 Field practice indicates that addition of foaming agent into steam can effectively decrease steam mobility and sequentially extend sweep volume of steam. Meanwhile, the foaming agent serves as a surfactant, which results in remarkable improvement of displacement efficiency.3-10 Foams are composed of a large number of gas/liquid interfaces or lamellae to control mobility, and they can be generated in steam channels so that the subsequently injected steam will be diverted to previously unswept or oil-rich regions in the reservoir.6,9 Although foams have relatively low fluid 1

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density due to high gas content, they can exhibit a viscosity that is enormously higher – often several orders of magnitude higher – than that of bulk gas or liquid phase.11 Many researches about foams have been conducted before, especially the performance of stability and foaming ability.12-15 The results demonstrated that the stability of foams acted as a critical factor for EOR processes in the reservoir.13 Currently, the combination of steam and foams has been widely adopted to improve performance of steam injection.3,6,7,12 Most foaming agents show excellent performance at relatively low temperature, while their performance becomes poorer with increased temperature. But the buried depth of 70% of heavy oil reservoirs in China is 600 − 1400 m, and the corresponding steam temperature is over 250°C, at which the weak stability of foaming agent is observed.12 Previously, few studies were reported on unified standard of evaluation method for foaming ability and stability of foaming agent at high temperature. At low temperature, the Waring Blender or Ross-Milles method is generally employed to determine foaming volume and half-life, which are used to evaluate foaming ability and stability.16,17 Furthermore, foam blocking capacity, typically characterized by foam resistance factor in porous media, is considered as an significant property to identify which foaming agent is suitable for steam-foam flooding in oil industry.18,19 In laboratory, the evaluation methods of foaming ability are all utilized effectively at temperatures below 100 oC, while they cannot efficiently accomplish performance evaluation of foaming agent at high temperatures (above 200 oC, even as high as 300 oC).20 In addition, the temperature conditions are constantly changing during the practical application of foams. Particularly, while steam and foam migrate in porous media, the temperature of heat front gradually declines, which brings a large impact on foaming ability and foam stability of foaming agent. But at present there is still no complete evaluation method for foaming ability and foam stability of foaming agent at variable temperatures. The foam fluid, which provides significant resistance to the flow of gas and water phase，is regarded as a selective blocking agent in porous media.21 Foam resistance factor is generally employed to characterize blocking ability of foams in laboratory. When liquid and gas flow simultaneously in porous media at a certain temperature, the steady-state pressure difference between the inlet and outlet is named as the basic pressure difference. When gas and foaming agent solution with the same flow rate flow simultaneously in porous media at the same temperature, the steady-state pressure difference between the inlet and outlet is named as the resistance pressure difference. Then the foam resistance factor is defined as the ratio between the resistance pressure 2


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difference and the basic pressure difference.9,21 The foam blocking ability is affected by many factors, including the concentration of foaming agent solution, gas-liquid ratio, reservoir permeability, oil saturation and temperature.22 Presently, the performance of foaming agent for thermal recovery has not been fully studied. What is more, the change of foaming agent performance with temperature is also a complicated process.14,15 Therefore, it is necessary to establish an evaluation method for foaming agents, which is essential in optimization of foaming agents for thermal recovery in heavy oil reservoir. Aiming at foaming agent for thermal recovery, which is used to improve the efficiency of steam flooding, the evaluation method of foaming ability and blocking ability of foams is incomplete under the conditions of steam injection. Particularly, at variable temperatures, few unified standards are focused on the static and dynamic evaluation on foam performance of foaming agent for thermal recovery. In this article, a quantitative evaluation method is established to choose the optimum foaming agent during steam injection in heavy oil reservoirs.

2 THEORY 2.1 Evaluation Parameters (1) Foaming volume (Vmax) is defined as the maximum volume of foam system for a certain volume of foaming agent solution after a certain time of shear effect at a certain temperature. The greater foaming volume is regarded as a stronger foaming ability. (2) Half-life (T1/2 ) is defined as the time taken by the volume of foam system from Vmax to a half at a certain temperature. The longer half-life is taken as a slower speed of liquid drainage from foam system and a better foam stability. (3) Foam comprehensive index (S) is defined as an integral value about foam volume vs. time from the initial time to the half-life at a certain temperature. It takes the two key influence factors, Vmax and T1/2, into consideration together to analyze the static performance of foams. As shown in Fig.1, the shaded area, whose value is equal to foam comprehensive index (S), reflects foaming ability and foam stability of foaming agent. Therefore, the value of S is greater, which reflects a better performance of foaming ability and foam stability.

Fig.1 Relationship of foam volume vs. time

(4) Average foam comprehensive index ( S ) is defined as an average of foam comprehensive 3


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index (S) at multiple temperatures during steam flooding, as shown in Fig.2. The curve about foam comprehensive index (S) vs. temperature (T) can be drawn according to the above calculation method. The weighted average of foam comprehensive index, called as the average foam comprehensive index ( S ), is equal to the shaded area that reflects the effect of temperature on the foam comprehensive index (S).

Fig.2 Foam comprehensive index at different temperatures

(5) Basic pressure difference (∆pb): When liquid and gas flow simultaneously in porous media at a certain temperature, the steady-state pressure difference between the inlet and outlet of sand-pack is called as the basic pressure difference.9,21 (6) Resistance pressure difference (∆pr): When foaming agent solution and gas flow simultaneously in porous media at a certain temperature, the steady-state pressure difference between the inlet and outlet of sand-pack is called as the resistance pressure difference.9,21 (7) Foam resistance factor (Rf): The ratio between the resistance pressure difference (∆pr) and the basic pressure difference (∆pb) at a certain temperature is called as the foam resistance factor.9,21 (8) Average foam resistance factor ( Rf ): The curve about foam resistance factor (Rf) vs. temperature (T) can be drawn at different temperatures, as shown in Fig.3. The weighted average of foam resistance factor, called as the average foam resistance factor, is equal to the shaded area that reflected the effect of temperature on the foam resistance factor (Rf).

Fig.3 Resistance factor at different temperatures

(9) Comprehensive value of foam performance (FSR): By introducing a weighted factor, f, we can calculate the weighted summation of the two ratios, such as the dimensionless average foam comprehensive index ( Si S max ) and the dimensionless average resistance factor ( Ri Rmax ). This value, called as the comprehensive value of foam performance (FSR), can be employed to objectively characterize the comprehensive performance of foaming ability, foam stability and blocking capacity during a process of temperature variation. 2.2 Evaluation Methods (1) Foaming Ability and Foam Stability In order to evaluate static performance of foaming agent, the foam comprehensive index (S) is 4


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introduced to consider the influence of foaming volume and half-life on foam performance. Fig.1 shows the curve of foaming volume vs. time at experimental temperatures. On the assumption that the relationship between foaming volume and time is expressed as V = f1 ( t ) , the foam comprehensive index (S) can be described as the equation (1). t1

S = ∫ 2 Vdt 0

(1)

where S is the foam comprehensive index, ml·min; t1/2 is the foam half-life, min; V is foam volume, ml. Due to temperature variation during thermal recovery, the performance of foaming ability and foam stability can hardly be kept constant, which necessitates a study of foam comprehensive performance at different temperatures. The curve of foam comprehensive index vs. temperature is shown in Fig.2. The average foam comprehensive index ( S ) is considered as an evaluation parameter for preliminary screen of foaming agent under conditions of steam injection. The average foam comprehensive index is calculated according to the equation (2). S=

Tn 1 SdT ∫ Tn − T1 T1

(2)

where S is the average foam comprehensive index, ml·min; T1 is the lowest experimental temperature, oC; Tn is the highest experimental temperature, oC. (2) Foam Blocking Ability As shown in Fig.3, the shaded area reflects the effect of temperature on foam resistance factor. Considering temperature variation, the equation (3) is employed to calculate the average foam resistance factor. R=

Tn 1 RdT ∫ T Tn − T1 1

(3)

where R is the foam resistance factor, dimensionless; R is the average foam resistance factor, dimensionless. (3) Comprehensive Evaluation Method On the basis of the average comprehensive index ( S ), the maximum of average comprehensive index ( S max ), the average resistance factor ( R ) and the maximum of average 5


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resistance factor ( Rmax ), a new evaluation parameter is introduced to characterize the comprehensive performance for different foaming agents during a process of temperature variation. This new parameter, called as the comprehensive value of foam performance (FSR), can be calculated according to the equation (4). FSR = f

Ri Si + (1 − f ) R max S max

(4)

where FSR is the comprehensive value of foam performance, dimensionless; Rmax is the maximum of average foam resistance factor among all foaming agents, dimensionless; S max is the maximum of average foam comprehensive index among all foaming agents, ml·min; f is a weighted factor.

2.3 Determination of weighted factor At the same temperatures, foaming ability and foam stability are measured to reflect the static performance of foaming agents. Then the foam resistance factor is measured to reflect the blocking ability of foams under the conditions of high temperature and high pressure. (1) The Normalization of Experimental Results A normalization method of the range is introduced to normalize the average foam comprehensive index ( S ) and the average foam resistance factor ( R ) according to the equation (5).

y=

x − xmin xmax − xmin

(5)

Where y is the normalization value of experimental results; x is the value of experimental results; xmax is the maximum among experimental results; xmin is the minimum among experimental results. (2) The Average of Normalization Values The equation (6) is used to calculate the average of normalization experimental results.

y=

yi n

∑ yi 1

Where y is the average of normalization values; n is the number of foaming agents. (3) The Standard Deviation of Normalization Values 6


(6)

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The equation (7) is utilized to calculate the standard deviation of normalization experimental results.

1 n ( yi − y )2 ∑ n i =1

σ=

(7)

Where σ is the standard deviation. (4) The Coefficient of Variation The coefficient of variation can be calculated according to the equation (8).

CV =

σ y

(8)

Where CV is the coefficient of variation. (5) The determination of weighted factor The weighted factor, f, can be calculated according to the equation (9).

f =

CV R CV S + CV R

(9)

Where CVR is the coefficient of variation of the average foam resistance factor; CVS is the coefficient of variation of the average foam comprehensive index.

3. EXPERIMENTAL APPARATUS AND METHODS 3.1 Experimental Materials (1) Foaming Agents In our experiments, the foaming agents for thermal recovery include five kinds, foaming agent A: ZWF-1 (milky white, weak acid), foaming agent B: GMH-1 (milky white, weak alkali), foaming agent C: HFA-3 (milky white (a bit yellow), weak alkali), foaming agent D: FP-2 (brown, weak acid) and foaming agent E: DRF-3 (black, neutral), as shown in Fig.4.

Fig.4 The appearances of foaming agents for thermal recovery

(2) Properties of Reservoir Fluids The experimental oil sample, prepared by degassing from an actual oilfield of China, is characterized by density of 0.9598 g/cm3, colloid and asphaltene content of 42%, wax content of 9.96%, sulfur content of 0.39% and freezing point of 21 oC. In addition, the degassed crude oil can be defined as extra heavy oil with the viscosity of 18749.0 mPa·s at reservoir temperature. 7


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The total salinity of formation water varies from 4620 to 4850 mg/L. The main cationic is K+ and Na+ with concentration of 1537 – 1645 mg/L. The main anion is Cl- with concentration of 1898 – 1995 mg/L. The concentration of HCO3- is 911 – 961 mg/L. The concentration of CO32- is lower, only 125 - 135 mg/L. (3) Other Experimental Materials Non-condensate gas used to generate foams is industrial nitrogen with a purity of 99%. The porous media is a sand-pack, whose length is 60 cm and diameter is 3.8 cm. And it is packed with glass beads of 160 meshes.

3.2 Experiments of Foaming Ability and Foam Stability Foaming ability and foam stability of foaming agents are, respectively, expressed by two important parameters: foaming volume and half-life at different temperatures. Aiming at foaming agent solution with a mass concentration of 0.5wt%, we respectively measure their foaming volume and half-life through visual reaction oven. The schematic of experimental apparatus is shown in Fig.5. It mainly contains one high temperature and high pressure reaction oven with visual window, one constant-flux pump, one high pressure nitrogen cylinder, one condensing system, one foaming agent solution tank and etc.. Fig. 5 Schematic of evaluation device for static performance of foaming agent

The experimental procedures are presented as follows: (1) 100mL foaming agent solution is taken into the high temperature and high pressure reaction oven. Then the inlet valve of reaction oven is shut; (2) The temperature of reaction oven is set at an experimental temperature for 2 hours at least. Furthermore, through the back-pressure valve, the outlet pressure of reaction oven is controlled 0.5MPa higher than the saturated steam pressure corresponding to the experimental temperature; (3) The electromagnetic agitator of reaction oven is switched on. After 5 minutes of continuous stir at an appropriate rotating speed, the volume of foam fluid, named as the foaming volume (Vmax) is recorded. Then the agitator is shut; (4) The foam volume as a function of time is measured. When the foam volume becomes a half of Vmax, the time taken is called half-life (T1/2); (5) In order to cool the reaction oven to room temperature for next experiment, the heating power of reaction oven is switched off; (6) The new foaming agent solution is injected into the reaction oven. Then the reaction oven

8


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is controlled at another experimental temperature to conduct a new experiment; (7) Based on the measured foaming volume and half-life of different foaming agents at multiple temperatures, the curves of S vs. temperature can be drawn according to the equation (1); (8) The equation (2) is employed to calculate the average foam comprehensive index ( S ) of different foaming agents; (9) The foaming agents are sorted according to the values of the average foam comprehensive index ( S ) in descending order. Eventually, the optimum foaming agent can be determined according to the static performance of foams.

3.3 Experiments of Blocking Ability The foam resistance factor is typically selected to investigate foam blocking ability in field and laboratory. However, because heat transfer leads to temperature variation during foam migration, the conventional resistance factor is difficult to characterize blocking performance of foaming agents for thermal recovery. In this article, aiming at foams in porous media at high temperature, the weighted average foam resistance factor is employed to evaluate blocking ability more objectively. The experimental apparatus includes one constant temperature oven, one steam generator, two injection pumps, one nitrogen cylinder, one gas mass flowmeter, two intermediate tanks, one back-pressure valve, one hand pump, one sand-pack of 60 cm in length and etc.. The experimental procedures are presented as follows: (1) The sand-pack is filled with glass beads of certain mesh and then the whole experimental apparatus are installed, as shown in Fig. 6. With the aid of high pressure nitrogen, the pressure test is conducted under the pressure of 10 MPa for 30 minutes to ensure no leakage; (2) Formation water is injected into sand-pack at a flow rate of 2 mL/min until it get to a steady state at the outlet. The porosity of sand-pack can be calculated according to the volume of water detained in sand-pack. Darcy's formula is employed to calculate the absolute permeability; (3) The electric heating belts are bound round experimental pipelines. The temperature of the constant temperature oven and the electric heating belts is controlled at an experimental temperature for 2 hours. Furthermore, the outlet pressure of sand-pack is controlled 0.5MPa higher than the corresponding saturated pressure by using the back-pressure valve; (4) Hot water (2mL/min) and nitrogen (100mL/min, standard conditions) are simultaneously injected into sand-pack. Until a steady state, the pressure difference between the inlet and outlet of sand-pack, named as the basic pressure difference (∆pb), is measured at this temperature; 9


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(5) Then foaming agent solution (2mL/min) and nitrogen (100mL/min, standard conditions) are simultaneously injected into sand-pack. Until a steady state, the pressure difference between the inlet and outlet of sand-pack, named as the resistance pressure difference(∆pr), is measured at the same temperature; (6) At this experimental temperature, the foam resistance factor is calculated according to the ratio between the resistance pressure difference (∆pr) and the basic pressure difference (∆pb); (7) The temperature of injected fluids and the whole system is adjusted to measure the foam resistance factor at another temperature; (8) Aiming at all the foaming agents, the curves of foam resistance factor vs. temperature are drawn. The equation (3) is employed to calculate the average foam resistance factor of each foaming agent; (9) All the foaming agents are sorted according to the values of the average foam resistance factor in descending order. The foaming agent with the best blocking ability can be recommended.

Fig. 6 Schematic of foam blocking ability experiments

4. EXPERIMENTAL RESULTS AND ANALYSIS 4.1 Determination of Shear Velocity Before measuring the foaming ability and foam stability at high temperature, an experiment is firstly carried out to choose an appropriate shear velocity to generate foams at 45 oC. At the constant temperature, 100ml solution of ZWF-1 (agent A) with a mass concentration of 5% is put into the visual reaction oven. The solution is stirred for 5 minutes under a fixed shear velocity. Then a micro photograph of foams is rapidly taken to count the number of bubbles within the field of vision. Finally, the average diameter of bubbles can be obtained. Fig.7 to Fig.12 depicts the size of bubbles and the distribution frequency of bubble diameter at different shear velocity. When the shear velocity is lower, the shear stress is weaker, which leads to a chaotic distribution of bubbles. Big bubbles are mixed up with many small bubbles. With the increased shear velocity, the big bubbles are stretched to burst into new small bubbles. Moreover, since more and more small bubbles are produced, the number of large bubbles reduces and the average bubble size decreases, as shown in Figs.7 to 9. When the shear velocity is kept at 3103 r/min, the average bubble size further diminishes and the number of small bubbles significantly increases. Within the field of vision, the equilibrium degree of bubble distribution is obviously improved and the average diameter of 10


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bubbles mainly distributes between 0.14 – 0.16 mm, as shown in Fig.10. When the shear velocity is above 3103 r/min, the higher speed makes the average bubble size further decline. Meanwhile, the number of small bubbles gradually increases due to higher shear velocity. However, the larger surface energy of small bubbles makes foam system weakly stable, which increases the coalescence speed among bubbles. Therefore, the phenomenon of chaotic distribution is observed again, as shown in Figs.11 to 12. Fig.7 Bubble size photo and diameter distribution at a shear velocity of 1171 r/min Fig.8 Bubble size photo and diameter distribution at a shear velocity of 2167 r/min Fig.9 Bubble size photo and diameter distribution at a shear velocity of 2645 r/min Fig.10 Bubble size photo and diameter distribution at a shear velocity of 3103 r/min Fig.11 Bubble size photo and diameter distribution at a shear velocity of 3575 r/min Fig.12 Bubble size photo and diameter distribution at a shear velocity of 4049 r/min

As the shear velocity increases, the average diameter of bubbles shows a reduction trend in the form of exponential decline, as shown in Fig.13. The foam half-life firstly increases and then decreases with the increase of shear velocity, as shown in Fig.14. The maximum of half-life is achieved when the shear velocity is at 3103 r/min. Meanwhile, the distribution of bubble size is most uniform among the six shear velocities. The peak of distribution frequency has arrived to 21.7% (diameter ranged from 0.07 mm to 0.08 mm). Therefore, foam stability is strongest when the shear velocity is maintained at 3103 r/min. Fig.13 The influence of shear velocity on foam diameter Fig.14 The influence of shear velocity on foam half-life

4.2 Foaming Ability and Foam Stability Aiming at the five kinds of foaming agents, labeled A (ZWF-1), B (GMH-1), C (HFA-3), D (FP-2) and E (DRF-3), respectively, the evaluation for foaming ability and foam stability is performed based on the above experimental procedures. The experimental results are shown in Fig.15 and Fig.16. Fig.15 indicates that except for agent B, the foaming volumes of four agents (A, C, D and E) gradually decreases with the increasing temperature. The reason is that agent B has poorer solubility at lower temperatures. When the temperature is over 90 oC, agent B is wholly dissolved into formation water resulting in the largest value of foaming volume. Then the foaming volume gradually decreases as temperature increases. Many points of intersection are observed among the curves of different foaming agents, as shown in Fig.15. As shown in Fig.16, the curves 11


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of half-life basically present down-trends with the increase of temperature. Meanwhile, many points of intersection also appeare among the curves of different agents. These results demonstrate that the optimum foaming agent can hardly be chosen only according to the two parameters, foaming volume and half-life. Fig.15 The foaming volume of foaming agents at different temperatures Fig.16 The half-life of foaming agents at different temperatures

4.3 Blocking Performance of Foams The foam resistance factors of the five foaming agents are measured at 50, 70, 100, 150, 200, 250 and 300 oC, respectively. The physical property of sand-packs is listed in Table1. Fig.17 depicts foam structure from the outlet of sand-pack at 50 oC and 200 oC, respectively. The results show that many tiny and uniform bubbles are produced from the outlet of sand-pack at 50 oC, while the bubbles are larger and more inhomogeneous at 200 oC. The tiny foams have stronger capacity in trapping gas. In another word, a large number of gas is dispersed to generate foam fluids. However, the size of foams increases significantly at high temperature. This implies that the stability of foams sharply decreases, which results in quick separation between gas and liquid from foam fluids.23 Table 1 Physical properties of sand-packs

1

Experimental temperature (oC) 50

244.90

35.99

2

70

60

3.8

160

249.53

36.67

1872.63

3

100

60

3.8

160

240.27

35.31

1748.96

4

150

60

3.8

160

244.90

35.99

1816.54

5

200

60

3.8

160

235.65

34.63

1736.27

6

250

60

3.8

160

241.97

35.56

1796.23

7

300

60

3.8

160

245.79

36.12

1845.75

Experimental series

The length of The diameter sand-pack of sand-pack (cm) (cm) 60 3.8

The size of glass beads (mesh) 160

Pore volume (mL)

Porosity (%)

Permeability (×10-3µm2) 1792.12

Fig.17 Comparison of foam generated at outlet at different temperatures

The experimental results are shown in Fig.18. The best foaming agent can hardly be determined since there are differences on resistance factor of the foaming agents at multiple temperatures. As listed in Table 2, on the basis of the experimental results, the equation (2) and the equation (3) are employed to calculate the average foam comprehensive index and the average foam resistance factor of the five foaming agents. Furthermore, the equation (5) – (8) can be used to calculate the normalization values, the standard deviations, the coefficients of variation and the weighted factors. It can be concluded that the blocking performance of foaming agents follows the order of A>E≈C>D>B, but the foam comprehensive index follows the order of A≈D>E>C>B, as 12


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shown in Table 2. Therefore, we can only determine the optimum foaming agent is A and the worst foaming agent is B, but we can not give an appropriate order of the five foaming agents according to the above results.

Fig.18 The resistance factor of foaming agents at different temperatures Table 2 The average foam parameter of different foaming agents Foaming agent

Parameter A Experiment S

C

D

The standard deviation

The coefficient of variation

The weighted factor

48.668

11.140

0.229

--

E

57.603 27.332 49.989 57.541 50.878

Normalization Experiment

R

B

The average

Normalization

0.778

0.705

0.368

0.522

0.467

109.542 69.039 97.041 86.193 97.769

1.000

91.916

13.618

0.148

--

0.565

0.336

0.595

0.533

1.000

0.000

0.000

0.749

0.691

0.998

0.423

0.709

4.4 Optimization of Foaming Agents Because foam fluids migrates under the conditions of temperature variation, neither static evaluation nor dynamic evaluation can reflect the actual foam performance during steam injection. Although the foam resistance factor is used to characterize dynamic performance of foams in porous media, it is difficult to reflect the blocking ability of foams under the conditions of temperature variation. In order to evaluate foam performance in a process of temperature variation, the parameters, including foaming volume, half-life, foam resistance factor and the others, are all adopted together. On the basis of the above experimental results, the equation (4) is employed to calculate the comprehensive value of foam performance (FSR) of the five foaming agents, as listed in Table 3. The value of weight factor, f, is equal to 0.533, as listed in Table 2. The comprehensive value for foam performance (FSR) ranks as follows: A>D>E>C>B. Therefore, the best foaming agent is agent A, as shown in Fig.19. Table 3 The table of performance evaluation for different foaming agents Category Measured value

Dimensionless value

Fig.19

S

A 57.603

B 27.332

Foaming agent C 49.989

D 57.541

E 50.878

R

109.542

69.039

97.041

86.193

97.769

S

1.000

0.474

0.868

0.999

0.883

R FSR

1.000

0.630

0.886

0.787

0.893

1.000

0.555

0.881

0.888

0.885

Parameter

Comparison of dimensionless values among the five foaming agents

5. FIELD APPLICATIONS The actual oilfield is characterized by the average net pay of 5.6m, the average depth of 220m, 13


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the average porosity of 34.82% and the average permeability of 2.25µm2. The oil layer shows serious heterogeneity in plane and vertical direction. Four inverted nine-spot well groups, L31513, L31713, L31717 and L31917, whose well spacing is 100m×141m (as shown in Fig. 20), were chosen to implement steam flooding pilot on Sept. 1, 2009. By the time of Jan. 8, 2010, steam has been injected for 130 days and the cumulative mass of injected steam was 2.91×104 tons. The cumulative liquid production was 2.46×104 m3. The cumulative oil production was 0.25×104 tons. The water cut has been over 90%. For single well, the average daily production of oil was only 0.8t/d and the oil-steam ratio was lower than 0.1, which mainly resulted from steam channeling among injection wells and production wells.24-26 Fig.20 Well pattern of steam flooding pilot

The profile control of foam injection was carried out in L31713 well group since July 12, 2010. Steam was injected into tubing at the injection rate of 54 t/d; Foaming agent A and nitrogen were injected into casing simultaneously to generate foams. The injection rate of foaming agent was 1.4 t/d and the injection rate of nitrogen was 6000 m3/d. As shown in Fig.21, when nitrogen and foaming agent were injected on July 12, 2010, the pressure of injection well dramatically increased by 86.4% (from 2.2 MPa to 4.1 MPa). And then the pressure of injection well showed reduction trend after foam injection was over. The response of injection pressure indicated that foam fluids effectively blocked steam channeling between injection wells and production wells. As shown in Fig.22, compared with steam flooding, a remarkable increase of oil production was observed after foam injection. The cumulative incremental oil production has reached 675.9 m3 until Oct. 31, 2010.

Fig.21 The curve of steam injection pressure

Fig.22 The histogram of monthly oil production

6. CONCLUSIONS (1) During thermal recovery in heavy oil reservoirs, the foaming agent is used to generate foams in a process of temperature variation. In consideration of temperature variation, a new method is established to objectively evaluate foaming agent for thermal recovery. (2) Based on the experimental results of foaming volume and half-life at different temperatures, a calculation method about the average foam comprehensive index is introduced to preliminarily 14


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choose foaming agents. Furthermore, a calculation method about the average foam resistance factor is introduced to measure the blocking ability of foams in porous media. (3) A new parameter, the comprehensive value of foam performance, defined as a weighted summation of static and dynamic characteristics of foam fluids, is employed to quantificationally evaluate foaming agents. Aiming at the experimental results, the weighted factor can be obtained through calculating the normalization values, the average, the standard deviation and the coefficient of variation. (4) Five kinds of foaming agents are evaluated according to the method introduced in this paper. Agent A, ZWF-1, is chosen as the optimum foaming agent. The pilot test of foam profile control is carried out in an actual oilfield of China. Within three and a half months after foam injection, the cumulative incremental oil production reaches 675.9 m3. The profile control of foam injection achieves a perfect effect.

ACKNOWLEDGEMENTS The study was supported by National Natural Science Foundation of China (51104165), National Science and Technology Major Projects of China (2016ZX05009001) and the Science Foundation of China University of Petroleum, Beijing (2462015YQ0202).

AUTHOR INFORMATION Corresponding Author *Telephone: +86-010-89739827. E-mail: [email protected]. Notes The authors declare no competing financial interest.

REFERENCES (1) Yang, C.Z.; Han, D.K. Present status of EOR in the Chinese petroleum industry and its future. J. Pet. Sci. Eng. 1991, 6, 175–189. (2) Li, S.Y.; Li, Z.M.; Li, B.F. Experimental study and application on profile control using high-temperature. J. Pet. Sci. Eng. 2011, 78, 567–574. (3) Doscher, T.M.; Kuuskra, V.A. Reviving heavy-oil reservoirs with foam and steam. Oil Gas J. 1982, 80, 102–105. (4) Al-Attar, H.H.; Evaluation of oil foam as a displacing phase to improve oil recovery: a 15


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laboratory study. J. Pet. Sci. Eng. 2011, 79, 101–112. (5) Farajzadeh, R.; Andrianov, A.; Krastev, R.; Hirasaki, G.J.; Rossen, W.R. Foam–oil interaction in porous media: implications for foam assisted enhanced oil recovery. Adv. Colloid Interface Sci. 2012, 183, 1–13. (6) Solbakken, J.S.; Skauge, A.; Aarra, M.G. Foam Performance in Low Permeability Laminated Sandstones. Energy Fuels 2014, 28 (2), 803–815. (7) Nikpoor, M.H.; Dejam, M.; Chen, Z.X.; Clarke, M. Chemical–Gravity–Thermal Diffusion Equilibrium in Two-Phase Non-isothermal Petroleum Reservoirs. Energy Fuels 2016, 30 (3), 2021–2034. (8) Friedmann, F.; Chen, W.H.; Gauglitz, P.A. Experimental and simulation study of high-temperature foam displacement in porous media. SPE J. 1991, 6, 37–45. (9) Dicksen, T.; Hirasaki, G.J.; Miller, C.A. Mobility of foam in heterogeneous media: Flow parallel and perpendicular to stratification. SPE J. 2002, 7, 203–212. (10) Shen, D.H.; Wu, Y.B.; Liang, S.X.; Luo, J.H. Thermal stability of foam during steam drive. Petrol. Explor. Develop. 2015, 42, 712–716. (11) Karin, M.; Idar, S. Surfactant concentration for foam formation and propagation in snorre reservoir core. J. Pet. Sci. Eng. 2001, 30, 105–119. (12) Zhou, G.H.; Song, X.W.; Wang, Q.W. Application of foam combination flooding in Shengli Oilfield. Pet. Explor. Dev. 2006, 3, 369–372. (13) Simjoo, M.; Rezaei, T.; Andrianov, A.; Zitha, P.L.J. Foam stability in the presence of oil: effect of surfactant concentration and oil type. Colloids Surf. A 2013, 438, 148–158. (14) Maini, B.B.; Ma, V. Relationship between foam stability measured in static tests and flow behavior of foams in porous media, Presented at the SPE Annual Technical Conference and Exhibition, Houston, Texas, 1984, SPE 13073. (15) Mannhardt, K.; Novosad, J.J.; Schramm, L.L. Comparative evaluation of foam stability to oil. SPE 60686, SPE Reserv. Eval. Eng. 2000, 3, 23–34. (16) Schramm, L.L.; Novosad, J.J. The destabilization of foams for improved oil recovery by crude oils: effect of the nature of the oil. J. Pet. Sci. Eng. 1992, 7, 77–90. (17) Suffridge, F.E.; Raterman, K.T.; Russell, G.C. Foam performance under reservoir conditions. Presented at the SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 1989, 16


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SPE 19691. (18) Marcano, L.; Gutierrez, X.S.; Perez, B.; Martinez, E. Effect of some physical–chemical variables on the formation and stability of foam in oil–gas systems and their correlation with the formation of foaming crude oil. Presented at the Latin American and Caribbean Petroleum Engineering Conference, Cartagena de India, Colombia, 31 May – 3 June, 2009, SPE-123060-MS. (19) Pacelli, L.J. Foam drainage in porous media. Transp. Porous Media 2003, 52, 1–16. (20) Lu, C.; Liu, H.; Lu, K.; Liu, Y.; Dong, X. The adaptability research of steam flooding assisted by nitrogen foam in Henan oilfield. Proceedings of the 6th International Petroleum Technology Conference, Beijing, China, 26-28 March, 2013. (21) Siddiqui, S.; Talabani, S.; Yang, J.; Saleh, S.T.; Islam, M.R. An experimental investigation of the diversion characteristics of foam in berea sandstone cores of contrasting permeabilities. J. Pet. Sci. Eng. 2003, 37, 51–67. (22) Du, X.G.; Hou, J.R.; Cheng, T.T.; Li, S.; Ma, Y.F. Evaluation of oil-tolerant foam for enhanced oil recovery: Laboratory study of a system of oil-tolerant foaming agents. J. Pet. Sci. Eng. 2014, 122, 428–438. (23) Jabbour, C.; Quintard, M.; Bertin, H.; Robin, M. Oil recovery by steam injection: three-phase flow effects. J. Pet. Sci. Eng. 1996, 16,109–130. (24) Zhao, G.; Dai, C.L.; Zhang, Y.H.; Chen, A.; Yan, Z.H.; Zhao, M.W. Enhanced foam stability by adding comb polymer gel for in-depth profile control in high temperature reservoirs. Colloids and Surfaces A: Physicochem. Eng. Aspects 2015, 48, 115–124. (25) Li, R.F.; Yan, W.; Liu, S.H.; Hirasaki, G.; Miller, C.A. Foam mobility control for surfactant enhanced oil recovery, SPE J. 2010, 15, 928–942. (26) Ali, J.; Burley, R.W.; Nutt, C.W. Foam enhanced oil recovery from sand packs, Chem. Eng. Res. Des. 1985, 63, 101–111. (27) Chen, M.; Yortsos, Y.C.; Rossen, W.R. Insights on foam generation in porous media from pore-network studies. Colloids Surf. A 2005, 256, 181–189.

17


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hV= f1 ( t )

Vhmax max

S

11 max 2 Vmax

h

2

0 Fig.1

t1 2

Relationship of foam volume vs. time


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S = f2 (T )

Ω T1 Fig.2

Tn

Foam comprehensive index at different temperatures


Energy & Fuels

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R = f3 (T )

Ψ T1

Tn

Fig.3 Resistance factor at different temperatures


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A: ZWF-1

B: GMH-1

C: HFA-3

D: FP-2

Fig.4 The appearances of foaming agents for thermal recovery


E: DRF-3

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Pressure gauge Outlet

Hand pump

Constant-flux pump Visual window

Foaming agent solution Kerosene

Inlet

Condensing system

High temperature and high pressure oven

N2 vessel

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Beaker

Fig. 5 Schematic of evaluation device for static performance of foaming agent


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Fig. 6 Schematic of foam blocking ability experiments


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16 14

Distribution frequency (%) 分布频率(%)

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

12 10 8 6 4 2 0 0.04～0.06 0.08～0.10 0.12～0.14 0.16～0.18 0.20～0.22 0.24～0.26 Bubble diameter (mm)(mm) 气泡直径

Fig.7 Bubble size photo and diameter distribution at a shear velocity of 1171 r/min


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14


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12 10 8 6 4 2 0 0.02～0.04

0.08～0.10

0.14～0.16

0.20～0.22

0.26～0.28

Bubble diameter (mm) (mm) 气泡直径



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14 12 10 8 6 4 2 0 0.04～0.06 0.08～0.10 0.12～0.14 0.16～0.18 0.20～0.22 0.24～0.26 (mm)(mm) Bubble diameter 气泡直径



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20 15 10 5 0 0.06～0.080.10～0.120.14～0.160.18～0.200.22～0.240.26～0.28 Bubble diameter (mm)(mm) 气泡直径



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16 14 12 分布频率(%)

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

10 8 6 4 2 0 0.06～0.080.10～0.120.14～0.160.18～0.200.22～0.240.26～0.28 气泡直径(mm)



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20 15 10 5 0 0.04～0.06 0.08～0.10 0.12～0.14 0.16～0.18 0.20～0.22 Bubble diameter (mm) (mm) 气泡直径



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0.4

Bubble diametermm (mm) 泡沫直径

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

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0.3

d 32 = 0.2653n

-0.7176

2

R = 0.9675

0.2

0.1

0.0 1711

2167

2645 3103 3575 Shearing rate r/min (r/mim) 转速

4049

Fig.13 The influence of shear velocity on foam diameter


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70 60 50 半衰期((min) min) Half-life

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40 30 20 10 0 2167

2645 3103 3575 r/min) Shearing (r/mim) 转速(rate

4049

Fig.14 The influence of shear velocity on foam half-life


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700 发泡体积(mL) Foaming volume (mL)

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

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600 500 400 300 200

A C E

100

B D

0 0

50

100

150

o Temperature ( ) ( C)

200

250

温度 ℃

Fig.15 The foaming volume of foaming agents at different temperatures


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250 200 半衰期(min) Half-life (min)

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150 100 A C E

50

B D

0 0

50

100

150

200

250

Temperature (oC) 温度(℃) Fig.16 The half-life of foaming agents at different temperatures


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50 oC

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200 oC

Fig.17 Comparison of foam generated at outlet at different temperatures


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250 200 阻力因子 Half-life (min) Resistance factor

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A C E

150

B D

100 50 0 0

50

100

150 200 250 o Temperature 温度(℃) ( C)

300

350

Fig.18 The resistance factor of foaming agents at different temperatures


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1.0 S 1000000000

R 2000000000

0.8

3FSR

Dimenssionless value

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

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0.6

0.4

0.2

0.0 A

Fig.19

B

C Foaming agents

D

E

Comparison of dimensionless values among the five foaming agents


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楼31211

LZ29 楼资29

楼31311 L31311

楼31413 L31413

L31513 楼31513

楼31411 L31411

楼31409

楼31719 L31719

L31615 楼31615

楼31715 L31715

楼31613 L31613

楼31511 L31511

楼31617 L31617

楼31717 L31717

楼31817 L31817

楼资30 LZ30

楼31919 L31919

楼资27 LZ27

楼31509 楼31611 L31611

楼31713 L31713

L31815 楼31815

楼31917 L31917

楼32017 L32017

楼31712 L31712 楼31915 L31915

楼31610 L31610

Injection well

L32019 楼32019

Production well

Fig.20 Well pattern of steam flooding pilot


楼32119 L32119

楼资31

Energy & Fuels

5

注汽压力(MPa) Injection pressure (MPa)

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4

3

2

1

0 2010.07.01

2010.07.07

2010.07.13

2010.07.19

2010.07.25

Date

Fig.21 The curve of steam injection pressure


2010.07.31

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400 月产油量(t) Oil production per month (m3)

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350

Before foam 调剖前 injection After foam injection 调剖后

300 250 200 150 100 50 0 2009.09 2009.11 2010.01 2010.03 2010.05 2010.07 2010.09

Date

Fig.22 The histogram of monthly oil production


Novel Evaluation Method of Foam Agents for Thermal Recovery in

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