Salt Tolerant Synthetic PolymersEffects on adsorption and retention

Masoud RashidiSigmund Sandvik

Anne Marit BlokhusArne Skauge

Presented by Ketil Djurhuus

IEA Collaborative Project on EOR30th Annual Workshop and Symposium

21-23 September, Canberra, Australia

Outline

• Introduction and motivation• Materials and experiments• Static and dynamic retention• Practical applications • Conclusions

Why polymer flooding?

1. Improve area sweep

2. Reduce viscous fingering

Before polymer flooding After polymer flooding

High mobility ratio Low mobility ratio

Limitations of conventional polymers

Salinity (w

t.%)

10

5

20

0 50 100 150Temperature (°C)

Xanthan

HPAM

Effects of polymer adsorption and retention

• Polymers accumulate adsorb at the solid/liquid interface.

• Polymer injection reduces permeability due to retention of polymer by adsorption and mechanical entrapment.

• Loss of polymer due to retention causes lower viscosity of fluid.

Materials• HPAM little salt tolerant

• Sulfonated copolymers have improved solution properties

• Sulfonation improves salt tolerance compared to carboxylates

• Sulfonated polymers areless prone to precipitation

Hydrolyzed polyacrylamide

Sulfonated polyacrylamide

Experimental plan

Polymers HPAM

AN 105 AN 113 AN125 AN 132

Sulfonation degree (mole %)

0 51 13 25 32

Polymers AN 125 VLM

AN125 AN125 VHM

Mw (MDalton)

2 8 12

Varying sulfonation degree Molecular weight = 8 MDalton

Varying molecular weight Sulfonation degree = 25 mole%

1 Molecular weight = 6 MDalton

Experiments

• Static adsorption– Two different minerals e.g. kaolinite and silica– Constant solid/liquid ratio to avoid flocculation.

• Dynamic retention– Berea outcrop sandstone– Injection of two pore volumes polymer with known

concentration followed by 3 pore volumes solvent– Tracer injected along with the polymer to detect any

difference in flow pattern

Static adsorption Adsorption isotherm on kaolinite. SD= 13% Mw = 8 MDalton

S/L= 0.005, T = 20C, Salinity = 5 wt% NaCl

0

100

200

300

400

500

600

700

800

0 50 100 150 200 250 300

Equilibrium concentration [ppm]

Ad

sorp

tio

n [

µg/m

2]

Static adsorption: Effect of sulfonationMw = 8 MDalton

S/L= 0.005, T = 20C

0

200

400

600

800

1000

1200

1400

1600

0 4 8 12 16 20 24 28 32 36

Sulfonation Degree [mole %]

Ad

sorp

tio

n [

μg

/m2]

SSW

5 w t% NaCl

HPAM

Static adsorption: Effect of molecular weightSulfonation degree = 25%

S/L= 0.005, T = 20C

0

200

400

600

800

1000

1200

1400

1600

0 2 4 6 8 10 12 14

Molecular weight [MDa]

Ad

sorp

tio

n [

μg

/m2]

SSW

5 w t% NaClHPAMHPAM

Dynamic retentionDynamic retention profile on a Berea core. SD= 25%

Mw = 12 MDalton. T = 20C. Salinity = SSW

Dynamic retention: Effect of sulfonationMw = 8 MDalton

T = 20C

0

20

40

60

80

100

120

140

0 4 8 12 16 20 24 28 32 36

Sulfonation Degree [mole %]

Ad

sorp

tio

n [

μg

/m2]

SSW

5 w t% NaCl

HPAM

Dynamic retention: Effect of molecular weightSulfonation degree = 25%

T = 20C

0

20

40

60

80

100

120

140

0 4 8 12 16

Molecular weight [MDa]

Ad

sorp

tio

n [

μg

/g]

SSW

5 w t% NaClHPAM

Practical applications Both retention and viscosity are important for practical use of

polymers

0

20

40

60

80

100

120

140

0 5 10 15 20 25 30 35

Sulfonation degree (mole %)

Ret

enti

on

(µ

g/g

)

0

5

10

15

20

25

30

35

Vis

cosi

ty (

mP

a.se

c)

Retention 5wt% NaCl

Viscosity 5wt% NaCl

Conclusions

• Sulfonated polyacrylamide polymers have considerably lower levels of both adsorption and retention than corresponding carboxylates

• Increasing the sulfonation degree reduces levels of both static adsorption and dynamic retention

• Static adsorption show an increasing trend with respect to increasing molecular weight

• Dynamic retention, however, show a decreasing trend with respect to increasing molecular weight

Conclusions

• At equal ionic strengths the presence of divalent cations leads to increased adsorption and retention

• Viscosity is maintained even at high sulfonation degree,but there is a substantial decrease in adsorption and retention

• This combination of factors makes samples with a high degree of sulfonation especially interesting for polymer flooding in high salinity reservoirs.