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“Quality, Integrity, Safety and Excellence”

Chemical Qualification of Corrosion Inhibitors in the Oil & Gas Industry: Impact of Test Approaches on Performance during Laboratory Screening

Electrochem 2019Technology Innovation Centre,

University of Strathclyde28th August 2019

Hunter ThomsonScaled Solutions Ltd.

Scaled Solutions

Internationally Recognised Independent Specialist Laboratory, Established 1999 • We specialise in Production Chemistry, Corrosion, Flow Assurance and Formation

Damage evaluation• Laboratory facilities in Livingston• International Client Base

• All Major operating companies • Chemical Vendors & Manufacturers

• Vision “Market leading partner globally for companies who need to solve challenges in relation to production chemistry, corrosion and formation damage”

• 2013 Opened First International Lab in Abu Dhabi • 2018 Office in Houston, USA – Lab in 2019

What We DoIn

tegr

ated

Production chemistry

Specialised field consultancy

Prediction, simulation and modelling

Scale control

Organic fouling

Corrosion control

Core flooding

Water injectivity and EOR

Analytical services – brine, oil, residuals and ESEM

Laboratory equipment manufacturing

1 to 1 R&D projects

Theoretical and practical training courses

Introduction• Maintaining integrity of oilfield equipment is essential to safe and efficient

production

• Controlled by system design & operations

- Many aspects required for control with chemical qualification at plausible worst-case conditions

• Qualifications usually involve screening a range of candidate chemicals

- An important aspect of accurate screening is the approach taken for each type of test as small changes could significantly impact outcome

- Parameters include, temperature, pressure, gases, hydrocarbon, wall shear stress, materials etc.

Background

• Typically use simplified, rapid tests to allow wide range of candidates

• Although simplified, conditions should be as representative of the field as possible - Which simplifications could lead to incorrect ranking?

• Here we examine how apparently small changes to these conditions can have significant impact on the outcome of chemical screening

Corrosion Inhibitor Qualification

• Cell contains fluid of interest

• 2 electrode set-up

– Same material as in the field

• Analysis by linear polarisation resistance (LPR)

– Open circuit potential measured

– Working electrode polarised and current density measured

– This can be used to calculate corrosion rate


CI FormulationsRange of corrosion inhibitors formulated, based on commonly used chemistries. Mosttests focussed on quaternary ammonium salt and phosphate ester.

All containing the same weight percentage of the respective active component,additives and solvents.

General performance investigated. Further tests focused on quaternary amine andphosphate ester.


• 50°C

• Ambient pressure

• 100% CO2

• 2 hours pre-corrosion

• pH 5.5

• Concentrations from 2.5 – 100 ppmv

Benchmark: achieve 0.1 mm/y within 2 hours of addition

Ion (mg/l)

Na+ 29358

Ca2+ 3145

Mg2+ 503

K+ 372

[SO4]2- 11

[HCO3]- 494

Synthetic Field Brine

Minimum Effective Dose (MED)Test Conditions

Minimum Effective Dose (MED)Results

Quaternary AmmoniumMED 10 ppmv

Phosphate Ester MED 25 ppmv

• 50°C


• 100% CO2

• 0, 2, 4, 20 hours pre-corrosion

• 16 hours post inhibitor addition

• Quat at 10 & 20 ppmv

• pH 5.5

Ion (mg/l)

Na+ 29358

Ca2+ 3145

Mg2+ 503

K+ 372

[SO4]2- 11

[HCO3]- 494


Effect of Pre-corrosionTest Conditions

Concentration: 10 ppmv

Active Component: Quaternary ammonium salt

Effect of Pre-corrosion

Effect of Pre-corrosion



• Maximum performance of the inhibitor appears to be achieved in tests withno pre-corrosion phase as a doubled dose rate results in a similar finalcorrosion rate

• At the higher CI concentration it can be seen that shortened pre-corrosionshows a clear trend of achieving a lower final corrosion rate

• 20 hour pre-corrosion tests see a borderline fail at (0.11 mm/y) improve to acomfortable pass (0.04 mm/y) by increasing the concentration

• Considerable time is required for 20 h pre-corrosion film formation (~5hr)compared to the shorter pre-corrosion tests (all < 1hr)

DiscussionEffect of Pre-corrosion

• 50°C

• 50% Watercut


• 100% CO2



• Quat at 10 ppmv

• Phosphate ester at 25 ppmv

• pH 5.5

Ion (mg/l)

Na+ 29358

Ca2+ 3145

Mg2+ 503

K+ 372

[SO4]2- 11

[HCO3]- 494


Test ConditionsDual-phase Dosing Methods

Brine

Oil

CI

CI

Oil added after CI mixed into oil

CI

CI

Method 1 Method 2 Method 3

Oil added after CI mixed into brine

Method 4

Dual-phase Dosing Methods



Active Component: Phosphate Ester

• Overall both inhibitors reduce the final corrosion rate to below 0.1 mm/yregardless of dosing method

• Summary of results:

• In this case, ranking of these inhibitors changes depending on dosingmethod used

Addition MethodFinal Corrosion Rate (mm/y)

Quat Phosphate Ester

100% Brine 0.02 0.03

1 0.02 0.04

2 0.02 0.05

3 0.07 0.04

4 0.02 0.04

Dual-phase Dosing MethodsDiscussion

• 50°C

• 50% Watercut


• 100% CO2

• 1, 2, 4 & 20 hour pre-partitioning


• Quat and phosphate ester at MED

• pH 5.5

Ion (mg/l)

Na+ 29358

Ca2+ 3145

Mg2+ 503

K+ 372

[SO4]2- 11

[HCO3]- 494


Pre-partitioning DurationTest Conditions

Pre-partitioning Duration



Longer pre-partitioning increases final rate


Pre-partitioning duration Wet Chemical CI Assay(ppmv)

1 10.3

2 8.3

4 7.4

20 7.1

Longer pre-partitioning decreases final rate



Active Component: Phosphate Ester

• Testing of Quat showed the longer the time allowed for pre-partitioning, the lowerthe availability of CI in the brine phase

• The availability of CI is shown in assay results table below which shows a moresignificant change from 1 to 4 hours than from 4 to 20 hours.

• The similarity between 4 and 20 hour pre-partitioning results suggest an equilibriumhas been reached

• The phosphate ester showed the opposite trend with lower corrosion rates at longerpre-partitioning times.

Pre-Partition Time (h)Corrosion Rate at 2h

(mm/y)Final Corrosion (mm/y)

Wet Chemical

CI Assay (ppmv)

1 0.03 0.03 10.27

2 0.03 0.02 8.17

4 0.05 0.06 7.41

20 0.05 0.05 7.14

Pre-partitioning DurationDiscussion


Pre-partitioningduration (hours)

Final Corrosion Rate (mm/y)

Quat Phosphate Ester

1 0.03 0.04

2 0.02 0.03

4 0.06 0.03

20 0.05 0.02

• Ranking of inhibitor might depend on pre-partitioning duration

• This will depend on the particular chemistries or formulations involved

Test Conditions

• 90°C

• Field: 2.5 bar CO2

• Saturation Ratio < 1

• Lab: Ambient pressure, 100% CO2

• Saturation Ratio = 4.6



• Quat at 5 ppmv

Ion (mg/l)Na+ 32000Ca2+ 5800Mg2+ 1600

K+ 360[SO4]2- 1800[HCO3]- 260

Scaling Field Brine

Self Scaling Brine Systems

Brine Composition [Ca2+] [Sr2+] [HCO3-] [SO4

2-]

Unadjusted 5800 360 260 1800

Anions Removed 5800 360 0 0

Anions Reduced 5800 360 150 450

Reduced [HCO3]- 5800 360 150 1800

Reduced [SO4]2- 5800 360 260 450

Ca Removed 0 360 260 1800

Sr Removed 5800 0 260 1800

Reduced Ca 1000 360 260 1800

Reduced Sr 5800 40 260 1800

Brine Composition [Ca2+] [Sr2+] [HCO3-] [SO4

2-]

Unadjusted 5800 360 260 1800

Anions Removed 5800 360 0 0

Anions Reduced 5800 360 150 450

Reduced [HCO3]- 5800 360 150 1800

Reduced [SO4]2- 5800 360 260 450

Ca Removed 0 360 260 1800

Sr Removed 5800 0 260 1800

Reduced Ca 1000 360 260 1800

Reduced Sr 5800 40 260 1800

Scaling Field Brine Composition AdjustmentsSelf Scaling Brine Systems

• Various options to control in tests – reducing / removing scaling ions, or adding scale inhibitor

• Higher pH and scaling tendency of the field brine under ambient pressure conditions could lead to a milder condition than that experienced in the field

Brine Composition [Ca2+] [HCO3-] pH Saturation Ratio

Field 5800 260 5.2 <1

Unadjusted lab 5800 260 5.6 4.6

Reduced [Ca2+] 1000 260 5.7 0.9

Reduced [HCO3-] 5800 150 5.3 1.6


Scaling of blank

Mitigated scaling of blank

Significant difference between unadjusted and scale controlled brines – in this case straddling the pass criterion


• Apparent minor adjustments to the way tests are conducted can havesignificant effect on CI performance

• This can lead to a significantly different outcome for a CI screening study

- Potentially changing ranking and selection of inhibitors

• It is key to select appropriate conditions

- These should be as representative as practicable, and whereparameters are uncertain, be prudently conservative

Conclusions

Thank you for your time

Contacts:

Other enquiries: [email protected]

Me: [email protected]

Dr Ian Carpenter, Corrosion Team Leader: [email protected]

Dr Paul Hammonds, R&D Manager: [email protected]

mailto:[email protected]




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