Development of Swelling-Rate-Controllable Particle Gels to

Enhance CO2 Flooding Sweep and Storage Efficiency

Project No. DE-FE0024558

Baojun BaiMissouri University of Science and Technology

U.S. Department of EnergyNational Energy Technology Laboratory

Mastering the Subsurface Through Technology Innovation, Partnerships and Collaboration:Carbon Storage and Oil and Natural Gas Technologies Review Meeting

August 13-16, 2018

(a) Before swelling (b) After swelling

Cross-linked polymer powder, Super Absorbent PolymerSize ranging from nano-meter to millimeter

Preformed Particle Gel (PPG)

2

3

Presentation Outline• Technical StatusMm-size Particle Gels for Super-K ChannelsMicro-/Nano-gels for Matrix Conformance Problems Nanogel transport, plugging and EOR mechanisms

• Lessons Learned• Accomplishments to Date• Synergy Opportunities• Project Summary• Acknowledgement• Appendix

(a) Before swelling (b) After swelling

4

Mm-size Particle Gels for Super-K ChannelsTarget Conformance Problems

Targets: Super-K Channels Our Solutions

Achievement: Synthesized mm-sized swelling delayed CO2 resistant PPGs (10 um- mm)

5

Product 1: Swelling Rate Controlled to Days

0 1 2 3 4

0

10

20

30

40

50

60

SR (v

/v)

Time (h)

Meet the requirement: development of swelling rate controllable PPG

0 5 10 15 20 25 300

10

20

30

40

SR (V

/V)

Time (Days)Fast swelling within one hour

Traditional PPGs

Delayed swelling to days

New monomer addition to traditional PPGs

The new product overcome some problems of traditional PPGs Fast swelling rate, leading to injectivity issue Unable to travel long distance, only for near well-bore treatment

1% NaCl1% NaCl

6

Product 2: Swelling Rate Controlled to Months

Product 2 is good for in-depth fluid diversion

2nd crosslinker addition to traditional PPGs

Meet the requirement: development of swelling rate controllable PPG

0 50 100 150 200 2500

10

20

30

40

50

60

70

SR (V

s/V0)

Time (Days)

45C

60C

Swelling kinetics and Temperature effect (1% NaCl)

7

Product 3:CO2 Triggered Swelling Delayed Particle Gel

particle size 1-2 mm; 45 ℃

0 5 10 15 20 25 300

20

40

Swel

ling

Ratio

(Vs/V

0) DI Water/sCO2

1% NaCl/sCO2

DI Water

Time (Days)

Product good for in-depth reservoir deployment

Delayed swelling to weeks

Meet the requirement: development of swelling rate controllable PPG

In absence of CO2, size of the gel would not increaseUpon CO2 flooding, the gel would increase to 4 times of its initial volume

0 50 100 150 200 2500

20

40

60

Swel

ling

Ratio

( Vs/

V 0)

Time (Days)

1% NaCl

DI Water

Delayed swelling to months particle size 1-2 mm; 45 ℃

Mm-sized CPPG (Product 1) Plugging Efficiency to CO2

8

0

20

40

60

0 5 10

Frrg

Injection flow rate, ml/min

40k Frr1 40k Frr2

CPPG Frr1 CPPG Frr2

Compare to 40K, CPPG has much better plugging efficiency to CO2.

K=~23 Darcy 1 wt% NaCl

9

Mm-sized CPPG (Product 3) Plugging Efficiency to CO2

CO2 flooding experiment setup.

Select cores (permeability 50md) and frac.

Place fully swollen gel particles into fracture until pressure increases to 1000 psi.

Inject sCO2 to test breakthrough pressure. Measure stable pressure at different flow rates.

Inject 2 PV brine. Shut in the core holder. Keep core holder temperature at 60 ℃.

Test sCO2 breakthrough pressure. Measure stable pressure at different flow rates.

Analyze data.

Procedures

Matrix Permeability Around 50 md

Stone Type Sandstone

Fracture Width 0.5 mm

Gel Particle Size 100-125 Micron

Brine Used 1wt.% NaCl

0

100

200

300

400

500

600

700

0 200 400 600 800 1000

Diffe

rent

ial P

ress

ure,

psi

Injection TIme, min

Before Shut-in

After Shut-in

10

Core Flooding Experiment: Supercritical CO2

“Self-healing” behavior: Supercritical CO2 reached breakthrough at 617 psi in first

CO2 flood. After shut-in, another breakthrough at 437 psi was detected.

CO2 residual resistance factors increased after shut-in.

Pressure difference throughout the core. SCO2 Frr at different injection rates, before and after shut-in.

Shut in for 3 days

sCO2 Breakthrough

1000

1500

2000

2500

0 0.5 1 1.5 2

Resid

ual R

esist

ance

Fac

tor

Injection Rate, mL/min

CO2 injection before shut-in

CO2 injection after shut-in

1.75 cc/min

1.25 cc/min

0.75 cc/min

0.5 cc/min

1.75 ml/min

1.25 ml/min0.75 ml/min 0.5 ml/min

CO2 Resistant Micro-/Nano-gels for Matrix Conformance Problems

11

Targets-Matrix Problem Solution

Achievement: Synthesized a series of swelling-delayed CO2 responsible nano-particle gels that can transport into the in-depth of a reservoir.

Swelling Rate Controllable Nano-gels

(a) (b)

Tunable sizes: in the range of nano to microns

Nano-gel in powder form SEM images

12

14

Swelling Rate Controllable Nano-gel

Fast swelling in minutes

Traditional HPAM nano-gels

Delayed swelling to weeks

Product 1: CO2 triggered Swelling

• Traditional HPAM nano-gels had fast swelling rate within minutes• Product 1 swelling delayed to weeks

0 20 40 60 80 100 120

200

400

600

Diam

eter

of n

anog

el (n

m)

Time (min)

swelling in minutes

0 20 40 600

100

200

300

400

500

Nano

-gel

Siz

e

Time (Days)

15

CO2 Responsive Nano-gel with Swelling Rate Control

Product 2: CO2 responsive monomer used for micro/nano-gels

Meet the requirement: development of swelling rate controllable nano-gels

0 60 120 180100

150

200

250

300

Diam

eter

of n

anog

el (n

m)

Time (h)

Controllable Delay

Water

CO2

0 60 120 180 240 300 360

10

20

30

Zeta

Pot

entia

l (m

V)

Time(h)

In the presence of CO2

Swelling could be delayed in a controllable fashion: water flooding for nano-geldelivery and CO2 flow induced the increase of nano-gel size.

CO2

Nano-gel Thermal Stability

CO2 resistant Nano-gels had better stability than HPAM-type of nanogelsat different temperatures.

1 10 100100

200

300

60 °C 40 °C

Aver

age D

iamete

r (nm

)

Time (Days)

25 °C

16

17

Transport and EOR Mechanisms of Nanogels

Nanogel physicochemical

properties

Rheology of nanogel

dispersionsNanogel at oil/water interface

Nanogel on rock surface

Transport behavior and

mechanisms in porous media

Interfacial tensionEmulsion stability

Adsorption kineticWettability alteration

18

Property Nonionic nanogel (NN) Anionic nanogel (AN) Cationic nanogel (CN)

Charge Neutral Negative Positive

Zeta potential (mV) -1.76 -35.90 34.75

Original diameter (nm） 59.00 88.12 65.83

Swollen diameter (nm) 220.14 241.62 151.14

Polydispersity index (PDI) 0.236 0.268 0.482

Swelling ratio 51.92 20.61 12.10

pH (1000 ppm in DI water) 7.8 7.0 4.9

10 100 1000 10000

0

5

10

15

20

25

30

35

NN

AN

Inte

nsity

(%)

Dh (nm)

CN

Physicochemical Properties of Nanogels

Nanogels with same size distribution and

different charges were synthesized and used

for following characterizations and

evaluations.

Nano-gel Plugging Efficiency to Matrix

The plugging efficiency of the nano-gel to CO2 is more than 90%.

0.0 0.5 1.0 1.5 2.0 2.50

5

10

15

20

25

30

35

Residual resistance factor Plugging efficiency

CO2 flow-rate (mL min-1)

Resi

dual

resi

stan

ce fa

ctor

90

92

94

96

98

100

Plug

ging

effi

cien

cy(%

)

19

20

Oil Recovery Improvement by Nanogel Injection

oil

0 2 4 6 8 10 120

20

40

60

80

100

Diffe

rent

ial p

ress

ure

(psi

)

Injection volume (PV)

0

5

10

15

20

Oil

reco

very

(%)

NN injection 2nd flooding1st flooding

0 2 4 6 8 10 12 14 16 180

20

40

60

80

100

Diffe

rent

ial p

ress

ure

(psi

)

CN injection 2nd flooding

Injection volume (PV)

1st flooding

0

5

10

15

20

25

Oil r

ecov

ery

(%)

Nanogel injection

2nd flooding

emulsion

Nanogel for emulsification

Nanogel for water diversion

Rock core: Berea sandstone (negative charged), Φ: 20.5%, K: 87 mD

21

10 100 1000 10000

0

5

10

15

20

25

30

35

40

Inte

rfac

ial t

ensi

on (m

N/m

)

Nanogel concentration (ppm)

AN

CN

NN

0 500 1000 1500 2000 2500 3000 3500

5

10

15

20

25

30

35

40

45

1000 NN 2000 NN 5000 NN 10000 NN

Inte

rfac

ial t

ensi

on (m

N/m

)

Time (s)

10 100 1000

10

20

30

40

0 200 400 600 800 10001200140016001800

5

10

15

20

25

30

35

1000 AN 2000 AN 5000 AN 10000 AN

Inte

rfac

ial t

ensi

on (m

N/m

)Time (s)

10 100 10005

1015202530

0 500 1000 1500 2000 250005

1015202530354045

1000 CN 2000 CN 5000 CN 10000 CN

Inte

rfac

ial t

ensi

on (m

N/m

)

Time (s)

10 100 10000

10

20

30

40

EOR Mechanism 1: Nanogels for Interfacial Tension Reduction

Nanogels can rapidly reduce the oil/water interfacial tension.

The equilibrium interfacial tension is related to the nanogel concentration.

The equilibrium interfacial tension becomes constant when nanogel concentration above 1000 ppm .

22

EOR Mechanism 2: Oil-in-Water Emulsion Stabilization

Nanogels can stabilize oil-in-water emulsion for more than 6 months.The diameter of emulsified oil drops is from several to tens of microns.

AN CN NN

O/w emulsions was prepared with decane and nanogel dispersion (1% NaCl) at 25 °C

23

Dynamic Adsorption and Desorption Tests

Nanogel concentration measurement

24

0 5 10 15 20

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Injection pressure Nanogel concentration

Injection volume (PV)

Inje

ctio

n pr

essu

re (p

si)

0

200

400

600

800

1000

1200

Efflu

ent n

anog

el c

once

ntra

tion

(ppm

)

NN adsorption

0 1 2 3 4

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Post injection volume (PV)

Inje

ctio

n pr

essu

re (p

si)

0

200

400

600

800

1000

1200

1400

Injection pressure Nanogel concentration

Efflu

ent n

anog

el c

once

ntra

tion

(ppm

)

NN desorption

0.00 0.25 0.50 0.75 1.00 1.25 1.50

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Injection volume (PV)

Inje

ctio

n pr

essu

re (p

si)

0

200

400

600

800

1000AN adsorption

Injection pressure Nanogel concentration

Efflu

ent n

anog

el c

once

ntra

tion

(ppm

)

0.0 0.1 0.2 0.3 0.4

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Post injection volume (PV)

Inje

ctio

n pr

essu

re (p

si)

0

200

400

600

800

1000AN desorption

Injection pressure Nanogel concentration

Efflu

ent n

anog

el c

once

ntra

tion

(ppm

)

0 5 10 15 20 25

0

2

4

6

8

10

12

14

Injection volume (PV)

Inje

ctio

n pr

essu

re (p

si)

0

250

500

750

1000CN adsorption

Injection pressure Nanogel concentration

Efflu

ent n

anog

el c

once

ntra

tion

(ppm

)

0.00 0.25 0.50 0.75 1.00 1.25

0

2

4

6

8

10

12

14

Injection pressure Nanogel concentration

Post injection volume (PV)

Inje

ctio

n pr

essu

re (p

si)

0

250

500

750

1000

1250CN desorption

Efflu

ent n

anog

el c

once

ntra

tion

(ppm

)

Dynamic Adsorption/Desorption of Nanogel

Nanogels are able to increase the injection pressure in sandstone saturated with water. Desorption process is depending on the electro-attraction between nanogel and rock.

Rock core: Berea sandstone (negative charged), Φ: 20.5%, K: 266.7mD

Adsorption:4.8 mg/g Adsorption:

5.3 mg/g

Adsorption:0.25 mg/g

Desorption:0.19 mg/g

Desorption:0.20 mg/gDesorption:

0.076 mg/g

Delivery of Nano-gel in Sandstone

25

# Diameter (mm) Length (mm) PV (cc) Permeability (md)

1 37.9 284 61.67 98

Core information

0 1 2 3 4 50

1

2

3

4

5

6

7

Frr

Flow rate (mL/min)

Permeability Reduction in Different Segments

28

𝐹𝐹𝐹𝐹𝐹𝐹 =𝑘𝑘𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑘𝑘𝑎𝑎𝑏𝑏𝑎𝑎𝑏𝑏𝑏𝑏

=𝑃𝑃𝑎𝑎𝑏𝑏𝑎𝑎𝑏𝑏𝑏𝑏𝑃𝑃𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 𝑞𝑞

Segment 2

Segment 1

• Nano-gel can be delivered into the far wellbore area• After CO2 stimulation, nano-gel provides a sufficient plugging to segment 2 and no penetration

to segments 3 and 4

Accomplishments to Date

29

• Published 11 journal papers, one conference paper, and two presentations.• Synthesized nano- to millimeter-sized swelling-rate controllable CPPGs for

different conformance problems.• Evaluated the effect of water salinity, pH and temperature on CPPG and

nanogel behavior.• The plugging efficiency of mm-sized CPPG to super-K channels is more than

90%.• Nanogel synthesized under scCO2 conditions have narrower distribution than

those synthesized by emulsion methods.• Nanogel can transport through Berea sandstone, improve oil recovery by

increasing both micro- and macro- displacement efficiency. • Nanogel can be placed in the far wellbore and provide efficient plugging under

scCO2 condition

Synergy Opportunities• Industry Interest for mm-sized CPPG product scale-up and field

pilot test. – Currently our industry collaborators Conoco-Phillips (CP), Occidental (OXY),

and Daqing Wantong are interested in the products for pilot tests. • CO2 Storage Partnership Projects

– The new products can be used to solve early breakthrough or excess CO2production problems for CO2 EOR storage projects.

• Swelling-rate controllable nano-particles for wellbore leakage control from minor cracks that cement can not penetrate.

31

Project Summary

32

Key findings:• The swelling-rate controllable CPPGs have been successfully

synthesized. Their sizes are adjustable from nano to millimeter.• The swelling rate of CPPG can be controlled from a few hours to up to

a few months. • The synthesized particle gels is thermo-stable in sCO2.• Mm-sized CPPG can effectively reduce CO2 permeability in super-K

channels and their plugging efficiency is over 90%.• The nanogel can transport through common porous media and form

efficient plugging in far wellbore zone under scCO2 condition.Next Steps:• Run coreflooding test to further understand nanogel transport and

blocking mechanisms.• Test whether swelling-rate-controllable nanogel can be used for leakage

control.• Write the final project report

Acknowledgement• US Department of Energy• Industry: Conoco-Philips, Occidental Petroleum

Corporation• Project Manager: Kylee Rice• Graduate students

33

Appendix– Benefit to the Program– Project Overview– Organization Chart– Gantt Chart– Bibliography

34

35

Benefit to the Program • Program goals being addressed

– Develop technologies to improve reservoir storage efficiency while ensuring containment effectiveness.

• Project benefits statement– The research project is to develop novel environmental friendly

swelling-rate-controllable particle gels to improve CO2 sweep and storage efficiency. The new materials will overcome some distinct drawbacks inherent in the in-situ gels that are traditionally used for conformance control. The technology, when successfully demonstrated, will provide a novel cost-effective technology to the Carbon Storage Program’s effort of improving reservoir storage efficiency while ensuring containment effectiveness.

36

Project Overview: Goals and Objectives (1)

• Overall Goal: to develop a novel particle-based gel technology that can be used to enhance CO2 sweep efficiency and thus improve CO2storage in mature oilfields.

• Project Objectives:– Synthesize swelling rate controllable CO2-based polymer network

nano-particles at supercritical CO2.– To understand the correlation of particle gels and CO2/water/oil

flow by core flooding tests.– To understand the plugging mechanisms of particle gels for

different types of reservoir problems.

Project Overview: Goals and Objectives (2)

• Relevance to Program Goals– Novel materials will improve CO2 storage efficiency while

ensuring containment effectiveness.

• Success criteria – Swelling rate controllable particle gels in nano-size– Resistance to supercritical CO2

– Plugging efficiency of CO2 resistant particle gels – Successful delivery of nano-gels into target locations– Understand the relationship of CO2/water/oil by core-flooding

tests in the presence of particle gels.

37

38

Organization Chart

PI: Baojun BaiCo-PI: Mingzhen Wei

Senior investigator: Dr Lizhu WangTechnician: Ninu MariaGraduate Students

Ms. Adriane MelnyczukMs. Xindi SunMr. Yifu LongMr. Jiaming Geng

39

Gantt ChartTechnical Tasks

2016 2017 2018

Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4

1.0 Project management and planning and reporting

2.0 Synthesis and characterization of particle gels

2.1 Synthesis and characterization of micro- to millimeter-sized particle gels

2.2 Synthesis and characterization of CO2-based polymer network nano-particle gels at supercritical CO2 fluids

3.0 transport behavior of millimeter-sized particle gel through fractures or fracture-like channels and their plugging efficiency to supercritical CO2 fluids

3.1 develop criteria for particles passing through pore throats and open fractures

3.2 conduct core-flooding tests to understand the effect of particle gels on CO2/water/oil flow

3.3 deliver nano-particle gels for in-depth placement

3.4 develop the mathematical models

Bibliography1. Wang, L.Z., Long, Y., Ding, H, Geng, B. Bai, B., 2017, Mechanically robust re-crosslinkable

polymeric hydrogels for water management of void space conduits containing reservoirs. ChemicalEngineering Journal, v. 317, p.952-960. available at: https://doi.org/10.1016/j.cej.2017.02.140

2. Imqam, A., Wang, Z. Bai, B., 2017, The plugging performance of preformed particle gel to waterflow through large opening void space conduits. Journal of Petroleum Science and Engineering. V.156,p.51-61. available at: https://doi.org/10.1016/j.petrol.2017.04.020

3. Imqam, A., Wang, Z. Bai, B., 2017, Preformed-particle-gel transport through heterogeneous void-space conduits. SPE Journal. V.22, issue 05, pp.1437-1447,available at: https://doi.org/10.2118/179705-PA

4. Sun, X.; Baojun Bai, B. Dehydration of Polyacrylamide-based Super-absorbent Polymer Swollen inDifferent Concentrations of Brine under CO2 Conditions. Fuel, 2017, 210, 32-40. available at:https://doi.org/10.1016/j.fuel.2017.08.047

5. Geng, J., Ding, H., Han, P., Wu, Y. and Bai, B., 2018. The transportation and potential enhancedoil recovery mechanisms of nanogels in sandstone. Energy & Fuels. available at:https://doi.org/10.1021/acs.energyfuels.8b01873

6. Sun, X., Suresh, S., Zhao, X. and Bai, B., 2018. Effect of supercritical CO2 on the dehydration ofpolyacrylamide-based super-absorbent polymer used for water management. Fuel, 224, pp.628-636.available at: https://doi.org/10.1016/j.fuel.2018.03.103

40

Bibliography7. Geng, J., Pu, J., Wang, L. and Bai, B., 2018. Surface charge effect of nanogel on emulsification of

oil in water for fossil energy recovery. Fuel, 223, pp.140-148. available at:https://doi.org/10.1016/j.fuel.2018.03.046

8. Sun, X., Alhuraishawy, A.K., Bai, B. and Wei, M., 2018. Combining preformed particle gel and lowsalinity waterflooding to improve conformance control in fractured reservoirs. Fuel, 221, pp.501-512. available at: https://doi.org/10.1016/j.fuel.2018.02.084

9. Alhuraishawy, A.K., Sun, X., Bai, B., Wei, M. and Imqam, A., 2018. Areal sweep efficiencyimprovement by integrating preformed particle gel and low salinity water flooding in fracturedreservoirs. Fuel, 221, pp.380-392. available at: https://doi.org/10.1016/j.fuel.2018.02.122

10. Wang, L., Geng, J. and Bai, B., 2018. Highly Deformable Nano-Cross-Linker-BridgedNanocomposite Hydrogels for Water Management of Oil Recovery. Energy & Fuels, 32(3), pp.3068-3076. available at: https://doi.org/10.1021/acs.energyfuels.7b03649

11. Pu, J., Zhou, J., Chen, Y. and Bai, B., 2017. Development of Thermotransformable ControlledHydrogel for Enhancing Oil Recovery. Energy & Fuels, 31(12), pp.13600-13609. available at:https://doi.org/10.1021/acs.energyfuels.7b03202

41

Filtration Test of Nanogel (Product 1)

42

Measure core absolute permeability

Put into coreholder and add confining pressure

(500 psi)

Inject brine at 1 cc/min until water produced

from the outlet

Inject 1000 ppm nanogelat constant pressure (10,

15, 20, 30 psi)

Collect effluent every 30 sec until the production

rate research stable

Experimental apparatus design

Experimental procedures

Core # Length (cm)

Diameter (cm)

Pore volume (mL)

Porosity (%)

Permeability (md)

D6 1.079 2.51 1.02 19.15 36B1 1.073 2.50 1.05 19.84 84

Core information

Filtration Test Results

43

36 md

84 md

0 50 100 150 200 250 3000.0

0.5

1.0

1.5

2.0

2.5

Q (m

L/m

in)

cumulative time (min)

0 20 40 60 80 100 1200

2

4

6

8

10

12

Q (m

L/m

in)

cumulative time (min)

10 psi

15 psi

20 psi

30 psi

10 psi15 psi 20 psi 30 psi

The rapid production rate reduction and low production rate indicate that the nanogel cannot flow through the rock with permeability lower than 36 md

0 1 2 3 4 5 6 7 8 9 10

10

15

20

25

30

Nano

gel i

njec

tion

pres

sure

(psi)

Q (mL/min)

84 md

0.00 0.02 0.04 0.06 0.08 0.10

10

15

20

25

30

Nano

gel i

njec

tion

pres

sure

(psi)

Q (mL/min)

36 md

Residual Resistant Factor

44

Filtration test

Inject brine to determine the

residual resistant factor

Take the core out and clean the

surface

0

50

100

150

200

250

0 0.2 0.4 0.6 0.8 1 1.2

Frr

Brine injection rate (cc/min)

Frr-before surface cleaningFrr-after surface cleaning

0

10

20

30

40

50

60

0 0.2 0.4 0.6 0.8 1 1.2

Frr

Brine injection rate (cc/min)

Frr-before surface cleaningFrr- after surface cleaning

36 md

84 md

• Nanogel forms external and internal cake near the inlet in the rock with permeability lower than 36 md

• Nanogel can penetrate through the sandstone rock with permeability higher than 80 md

45

Nanogel Injection

• No pressure buildup at P1 and P2 during the nanogel injection• Nanogel can penetrate into the in-depth without forming surface plugging

46

0 2000 4000 6000 8000 10000

1

2

3

4

5

6

K-D model

NN

CN

Rel

ativ

e vi

scos

ity

Nanogel Concentration (mg/L)

AN

Rheology of Nanogel Dispersions

Krieger-Dougherty model:

The nanogel dispersions have a concentration-related rheology.

The interparticle reactions increase the viscosity of dispersions with high nanogel concentrations.

solvent viscosity

viscosity

Rigid nanoparticles

25 °C, 6 s-1

1% NaCl

Initial Study of Nano-gel Plugging Efficiency to Matrix

The plugging efficiency of the nano-gel to CO2 is more than 90%.

0.0 0.5 1.0 1.5 2.0 2.50

5

10

15

20

25

30

35

Residual resistance factor Plugging efficiency

CO2 flow-rate (mL min-1)

Resi

dual

resi

stan

ce fa

ctor

90

92

94

96

98

100

Plug

ging

effi

cien

cy(%

)

47

48

0 5000 10000 15000 200000

1

2

3

4

5

6

7

Pseudo-second order

Pseudo-first orderCN

AN

Ads

orpt

ion

(mg/

g)

Time (min)

NNPseudo-second order

Control Sample NN AN CN05

101520253035404550

Cont

act a

ngle

(°)

Nanogel for Rock Surface Wettability Alteration

The adsorption of nanogel on rock surface is controlled by electrostatic interactions.

Nanogels with proper hydrophilicities can alter rock surface to more water-wet.

Immerse core in nanogel dispersion

Φ=20.50%K=87.21mD

Nano-gel Synthesis and Evaluation

CO2 delivery pump

Synthesis under supercritical CO2

Reactor system

CO2 reactor

12

Nano-gel Plugging Efficiency after CO2 stimulation

50

Measure core absolute

permeability

Inject 5 PV nano-gel into

the cores

Put one core in the vessel and pressurize the

vessel using CO2to 1100 psi

Put the vessel into the 65 ℃ oven

and take the core out after 7 days

Inject brine to determine the

residual resistant factor

Inject brine into one core to determine the residual

resistant factor

• The plugging efficiency improved after CO2 stimulation in 40 md cores • There exists matching ratio between particle size and rock permeability for efficient plugging

0.00 0.25 0.50 0.75 1.000

10

20

30

40

50

60

After CO2 treatment

Resid

ual r

esist

ant f

acto

rFlow rate (mL/min)

Rock permeability: 40 md

51

Size Increase under CO2 Condition

Meet the requirement: development of CO2 resistant nano-gels

CO2

Acid labile crosslinker

stable crosslinker

Product 1

Product 2