A Comprehensive Study of the Formation, Identification and Removal of Common Inorganic Oilfield Scale with Practical

Investigation in the Potential Application of Protic Ionic Liquids for Scale Removal

James Ciaran O’Hare (1611523)Supervisor: Dr Cathy McCullagh

MSc Oil and Gas Engineering

EI Best Student Paper Competition, Aker Solutions, 28th November 2017

Background• What is inorganic oilfield scale?

• What impact does it have?• 28% decline in North Sea production levels • USD 1.4 Billion global impact, 30% in North

Sea

• Most common forms of scale in industry are:• Carbonates (Calcium)• Sulphates (Barium, Strontium, Calcium)• Sulphides (Lead, Zinc and Iron)• Salts (Sodium Chloride – Halite)

• What causes scale…..

USD 400 million

Total Global Estimate of Scale Cost

Africa/ Far East

Russia

North and South America

ME

North Sea

Pie chart courtesy of Frenier and Ziauddin (2008b)

Causes of Scale formation

Figure 1: Courtesy of Bellarby (2009) Figure 2. Courtesy of Frenier and Ziauddin (2008a)

Mechanisms of Scale Formation

Figure 3: Scale deposition mechanism, courtesy of Cowan and Weintritt (1976)

Figure 4: Homogeneous (left)/ Heterogeneous (right) nucleation process of scale formation, courtesy of Crabtree et al. (1999)

Removal methods

• Chemical:• Matrix acidizing

• Chelating agents (e.g. EDTA)

• Scale inhibition treatment –continuous or squeeze

• Mechanical:• Coiled tubing milling• Wireline milling (e-line)• Jetting

Courtesy of Welltec (2017a)

Courtesy of Welltec (2017b)

Use of Ionic Liquids…

Applications:

• Corrosion and shale inhibitors (Berry et al. 2008).• Dissolution of asphaltene from heavy crude (Liu et al. 2005).• Scale inhibition delivered downhole via microspheres (Lakshmi et al.

2013)

2 broad categories of ionic liquids – aprotic and protic ionic liquid:

• Most research focuses on aprotic ILs• The works of Greaves et al. (2006) suggests that the physicochemical

properties of protic ionic liquids (PILs) are promising and could surpass the applications of aprotic ionic liquids

Methodology

Practical investigation:

• Material Preparation• Rig Design• Brine preparation• Solubility testing• Corrosion Observation• Scale formation and dissolution in PILs

Solubility

• Experiment carried out to determine solubility of calcium carbonate in PILs

• Using solubility of water as guideline

• Solubility could not be determined – solubility decreases with increasing temperature

Corrosion Behavior Study

• Observations were made over a period of 21 days• No change observed for the metal samples in either of the PILs• All reacted with hydrochloric acid – in particular stainless steel

Scale Formation

Stainless Steel Mild Steel Aluminium

Clean Sample Scaled Sample

HEAF(2-hydroxy ethylammonium formate)

TEAF(triethylammonium formate )

DEAF(diethylammonium formate )

15% wt. HCl(hydrochloric acid)

Conclusions

• PILs were effective in removing calcite scale

• This was due to ionic activity between the anion and cation of PILs

• An effective rig design mimicked the deposition of scale on pipe walls to provide an accurate scale surface to assess the behaviour of protic ionic liquids in dissolving calcite scale

• SEM analysis confirmed the correct polymorph of calcium carbonate scale had formed

• SEM and X-Ray analysis determined that HEAF, and TEAF, were highly effective in removing calcite - these were compared to 15% wt. hydrochloric acid

References

• FRENIER, W.W. and ZIAUDDIN, M., 2008a. Formation, Removal, and Inhibition of Inorganic Scale in the Oilfield Environment, Chapter 2: Inorganic Scale Chemistry, 2.2.2 Carbonate Scales, pp. 28-33. First ed. United States of America: Society of Petroleum Engineers.

• CRABTREE, M. et al., 1999. Fighting Scale - Removal and Prevention. Schlumberger Oilfield Review, Autumn. • FRENIER, W.W. and ZIAUDDIN, M., 2008b. Formation, Removal and Inhibition of Inorganic Scale in the Oilfield Environment; Chapter 1 -

Introduction, 1.5 Economic Impact of Scale, pp.11-12. United States of America: Society of Petroleum Engineers.• COWAN, J.C. and WEINTRITT, D.J., 1976. Water-Formed Scale Deposits, Chapter 6: Scale Deposition Mechanisms, pp. 204. Houston, Texas:

Gulf Publishing Company.• BELLARBY, J., 2009. Well Completion Design, Chapter 7: Production Chemistry, 7.1 Mineral Scale, pp. 381. First ed. Oxford, UK: Elsevier

• WELLTEC, 2017a. Clean-out solutions. [online] Welltec. Available from: http://www.welltec.com/wp-content/uploads/2016/08/CLEAN-OUT-BROCHURE_2016_low-res.pdf 2017]

• WELLTEC, 2017b. Conveyance solutions. [online] Welltec. Available from: http://www.welltec.com/solutions/conveyance/ 2017]

• BERRY, S.L. et al., 2008. Performance Evaluation of Ionic Liquids as a Clay Stabilizer and Shale Inhibitor. SPE-112540-MS

• LIU, Y. et al., 2005. Ionic Liquids: Novel solvents for petroleum asphaltenes. 13(4), pp. 564-567

• LAKSHMI, D.S. et al., 2013. Application of ionic liquid polymeric microspheres in oilfield scale control process, Journal of Petroleum Science and Engineering. 112, pp. 69-77

• GREAVES, T.L. et al., 2006. Protic Ionic Liquids: Solvents with Tunable Phase Behaviour and Physicochemical Properties, J. Phys. Chem., pp. 22479-22487. 110

• WANG, H. et al., 2013. Formation of CaCO3 Deposits on Hard Surfaces - Effect of Bulk Solution Conditions and Surface Properties.American Chemical Society Publications, pp. 4035-4045

Questions?

What are protic ionic liquids?

Protic Ionic Liquid:

“Protic solvents prepared through the stoichiometric combination (by proton transfer) of a primary amine with a Brønsted acid”

Protic meaning a hydrogen atom bonded to an oxygen, or in this case, an amine group (H-N)

Rig set-up and deposition

Clean Stainless Steel Sample

Scaled Sample

HEAF(2-hydroxy ethylammonium formate)

DEAF(diethylammonium formate )

TEAF(triethylammonium formate )

15% wt. HCl