Impact of dissolved iron species {Fe(II) and Fe(III)} inhibition efficiency of various chemical

inhibitors on barite scale formation.

April Zhang

1

Fe in produced water

2

Corrosion Siderite (FeCO3) formation

Fe(II) main source

Fe(III) can be formed by Fe(II) reduction of H+, dissolution of magnetite or other Fe(III) containing minerals or when produced water is exposed to air.

Fe(II) concentration varies from several mg/L to several thousand mg/L depending on well condition.

3

Fe(II) Soluble in water at acidic and near neutral pH

condition, can precipitate as ferrous hydroxide at pH 8 or higher.

Strong interaction with common inhibitor function groups, precipitate with phosphonates.

Fe(III) Extremely insoluble in water (9.46*10-7 mg/L at pH

7.0, 70oC), only soluble at acidic condition (pH 2.0 or lower).

Precipitate in water as various kinds of ferric hydroxide minerals, very strong surface adsorption ability.

Research purpose

Show a method to test Fe(II) and Fe(III) influence on scale inhibitor

Discuss the mechanism of how Fe(II)/Fe(III) influence scale inhibitor performance

4

Outline1. Fe(II) testing apparatus improvement2. Experimental result of Fe(II) effect of scale

inhibitor using the new apparatus3. Fe(III) effect on scale inhibitor and mechanism

investigation4. Application of organic chelating agents on

reversing Fe(III) effect on scale inhibitors 5. Conclusion and future work

5

Fe(II) testing apparatus improvement and Fe(II) effect on scale inhibitor

6

Injection linevent line

reactor

pure

Arg

on g

asOxygen

scavenger

pure

Arg

on g

as

Waste line

Argon line

Switch valve

7Water bath

Ba2+ SO42- inhibitor Fe2+

8

Switch valve

syringe

Stock solution bottles Injection line

Argon purge line

Vent line

ReactorWater bath

9

Inhibitor no. Active chemicals

C1 Phosphonates (single structure non-polymeric)

C3 Phosphonates (single structure non-polymeric)

C6 Polymer with carboxylate acid

C10 polymer with 2-propenoic acid

C11 Phosphorous incorporated maleic polymer

C13 Polymer with sodium 2-propane-1-sulfonate

C14 Polymeric non-phosphorous based

C15 Polymeric non-phosphorous based

C16 Poly(vinyl sulfonic acid) sodium salt

C17 Phosphonates (blend of different structures, non-polymeric)

Types of scale inhibitor tested

10

Inhibitor no.Inhibitor

conc. (ppm)Fe conc. (mg/L) Induction time (s) Result

No inhibitor 0 0 20C17 0.6 0 617

0.6 17 743 No effectC1 0.6 0 696

0.6 17 50 Significant impairmentC3 1 0 1495

1 17 50 Significant impairmentC16 1.92 0 449

1.92 1 436 No effect1.92 17 484 No effect1.92 26 414 No effect1.92 50 452 No effect

Experimental condition: 1M NaCl, pH=6.74, 400 mg/L Ca2+ , 70oC, barite SI=2.0

Experimental result of Fe(II) effect on scale inhibitor

Inhibitor no.Inhibitor conc.

(ppm)Fe conc.

(mg/L) Induction time (s) ResultC6 0.5 0 317

0.5 17 392 No effect0.5 50 416 No effect

C10 1 0 12241 17 1216 No effect

C11 1 0 4261 50 468 No effect

C13 1.92 0 3071.92 50 436 No effect

C14 1.92 0 5361.92 50 628 No effect

C15 1.92 0 3071.92 50 387 No effect

11

Polymeric scale inhibitors show good Fe(II) tolerance at experimental condition, some phosphonates were significantly impaired by Fe(II).

12

Precipitation of Fe(II) with phosphonates

At I = 1M, T = 70oC condition, solubility of Fe2.5HNTMP is CFe

= 0.019 mg/L, CNTMP= 0.04 mg/L

Fe2.5HNTMP

pKsp= 39.54 – 6.14 I ½ + 2.18 I – 1315 / T

70 90 110 130 150 170 190 210 2300

5

10

15

20

25

Comparison of solubility product of Fe and Ca-NTMP precipitate

Fe2.5HNTMPCa2.5HNTMP

Temperature (oF)

pKsp

<< Conc. Used in this research

More insoluble than Ca-phosphonate precipitate

NTMP

Fe(III) effect on scale inhibitor and mechanism investigation

13

Fe(III) impairs scale inhibitor performance

14

Exp#DTPMP

(ppm)PPCA

(ppm)PVS

(ppm)Fe(III)(ppm)

tind (s)

1 0 0 0 0 20

2 1.22 0 0 0 2062

3 1.22 0 0 1.00 41

4 1.92 0 0 0 23039

5 1.92 0 0 1.00 403

6 0 1.22 0 0 987

7 0 1.22 0 1.00 42

8 0 0 1.22 0 600

9 0 0 1.22 1.00 67

70oC, pH 6.74, 400 mg/L Ca2+, barite SI=2.0

Hypothesis for the mechanism of Fe(III) effect on scale inhibitorInhibitor gets absorbed onto ferric hydroxide particle, remaining inhibitor provide inhibition effect for barite nucleation

15

inh

inh inh

inhinh

inhinh inh

inh inh

inh

inh

inh

Ba2+ Ba2+

Ba2+SO42-SO4

2-

Observed barite inhibition time

Remaining inhibitor conc. in aqueous phase

The amount of inhibitor disappeared from aqueous phase is in the solid phase

Need accurate inhibitor concentration measurement

Inhibitor loss in aqueous phaseFe(III) solution

Ferric hydroxide particles

~

Measurement of DTPMP in the presence of Fe(III) in aqueous and solid phase

1. Mixing brine (1M NaCl, pH 6.74, 400 mg/L Ca2+ ), Fe(III) and DTPMPat room temperature

2. Analytical ultracentrifuge, 45000 rpm, 40min, room temperature

supernatant

3. ICP OES measurement

4. Acidify rest of the solution, dissolve particles and measure Fe and DTPMP conc. Using ICP-OES

16

17

Measurement results

1M NaCl, pH 6.7, 400 mg/L Ca2+ , 25oC, barite SI=2.4

Brine + Ba2+ + SO42-

2.29ppm DTPMP + 1 mg/L Fe(III)

278s

1273s

The amount of inhibitor lost from water is found in dissolved iron hydroxide particles

Barite inhibition times matches well with remaining DTPMP conc. in solution

Initial condition Barite nucleation induction time

Measured remaining DTPMP conc. in

solution

1.27 ppm

2.03 ppmBrine + Ba2+ + SO4

2- 3.00ppm DTPMP + 1 mg/L Fe(III)

DTPMP conc. (ppm) tind

0 31s

0.82 169s

1.22 230s

2 1183s

18

Application of organic chelating agents on reversing Fe(III) effect on scale inhibitors

EDTA Citric acid

logarithm of stability constant with Fe(III)EDTA 25.7

Citric acid 11.85

19

1

2

3

4

5

6

7

8

0 200 400 600 800 1000 1200 1400 1600 1800

induction time (s)

Barite only

1.15ppm DTPMP

Citric acid can gradually reverse Fe(III) effect on DTPMP

1.15ppm DTPMP, 0.4 mg/L Fe(III)

3:1Cit acid (4.11 mg/L)

1:1Cit acid (1.37 mg/L)

5:1Cit acid (6.85 mg/L)

10:1Cit acid (13.7 mg/L)

15:1Cit acid (20.55 mg/L)

70oC, barite SI=2.0, 400 mg/L Ca2+ , 1M NaCl, pH=6.74

Fe(III) chelated % by citric acid

0.107%

0.071%

0.036%

0.021%

0%

All contain 1.15ppm DTPMP, 0.4 mg/L Fe(III)

Citric: Fe(III) molar ratio

19

20

Barite only

1.15ppm DTPMP

1.15ppm DTPMP, 0.4 mg/L Fe(III)

1:1EDTA (2.08 mg/L)

3:1EDTA (6.25 mg/L)

5:1 EDTA (10.43 mg/L)

10:1EDTA (20.86 mg/L)

15:1EDTA (31.29 mg/L)

30:1EDTA (62.57 mg/L)

EDTA can also reverse Fe(III) effect, but not as well as citric acid

1

2

3

4

5

6

7

8

9

10

0 200 400 600 800 1000 1200 1400 1600 1800

50:1 EDTA (104.28 mg/L)

70oC, barite SI=2.0, 400 mg/L Ca2+, 1M NaCl, pH=6.74

Fe(III) chelated % by EDTA 100%

100%

100%

100%

100%

100%

93%

Induction time (s)

All contain 1.15ppm DTPMP, 0.4 mg/L Fe(III)

EDTA: Fe(III) molar ratio

Why citric acid works better than EDTA when EDTA is the stronger chelating agent?

21

Why do we need EDTA at 50:1 ratio to 0.4 mg/L Fe(III) to reverse the effect?

EDTA works by direct chelation of Fe(III) at a 1:1 ratio. EDTA needs to be provided 1:1 as stock solution concentration.

Citric acid works by adsorbing onto ferric hydroxide particles. Citric acid can be strongly adsorbed on ferric hydroxide significantly (Cornell et al. 1980)

Fe(III) stock solution diluted to 0.4 mg/L

26 mg/L Fe(III)

stock solution

Brine + Ba2+ + SO42-

+ DTPMP + chelating agents

1

2

3

4

0 200 400 600 800 1000 1200 1400

22

70oC, 1M NaCl, barite SI=2.0, pH 6.74

Fe(III) stock solution and EDTA are pre-mixed at 1:1 at pH=2.0

Another proof of EDTA working by direct chelation of Fe(III)

Barite only

1.15ppm DTPMP

1.15ppm DTPMP, 1 mg/L Fe(III)

ConclusionPolymeric scale inhibitors show good Fe(II) tolerance at

experimental condition while the inhibition performance of phosphonates were significantly impaired by Fe(II).

The mechanism of Fe(III) on scale inhibitor was experimental proved to be the adsorption of scale inhibitor onto ferric hydroxide nanoparticles in solution. If inhibitors are added in excess of the adsorption ability of the ferric hydroxide particles, remaining scale inhibitors in the aqueous phase can still provide inhibition.

Citric acid can reverse Fe(III) detrimental effect on DTPMP by adsorption onto ferric hydroxide surface and reduce the amount of inhibitor adsorbed onto ferric hydroxide.

EDTA can reverse Fe(III) detrimental effect on DTPMP by direct chelation of Fe(III) in solution.

23

24

Future workTest more inhibitors at higher Fe(II) concentration and higher

temperature Fe(II) effect in CaCO3 system. Its effect on CaCO3 nucleation and

inhibitor performance

Thank you!