Exploration & Production - Oil and Gas review

Effects of Corrosion Inhibitors and Surface Coverage on Pipeline Wall Wettability in Multiphase Systems

Table 1: Interfacial Tension Measurements Test No. Medium

1 2–6 7 8–12 Synthetic brine

Partitioned brine using 5 different inhibitors Synthetic brine

Fluid (drop) Temperature

Inhibitor-free oil 20°C Partitioned oil

Partitioned brine using five Partitioned oil different inhibitors

Note: 50–50 oil–brine ratios were used to prepare the partitioned brine and oil

Table 2: Contact Angle Measurements (Room Temperature) Test No.

1 2

3–7 8

9–13 14 15

16–20 21–25

26–30 FeS = iron sulphide. Figure 1: Photo of the Interfacial Tension/Contact Angle Apparatus

Material Bare steel Bare steel Bare steel

Brine wetted steel

Partitioned brine wetted steel FeS-coated steel FeS-coated steel FeS-coated steel

FeS-coated steel + wetted with partitioned brine

FeS-coated steel + wetted with partitioned brine

Fluid

Inhibitor-free oil Synthetic brine Partitioned brine Oil Oil Oil

Synthetic brine Partitioned brine Oil

Partitioned oil 20°C

Inhibitor-free oil 55°C 55°C

Figure 3: Typical Interfacial Tension Results for an Inhabited System Oil/brine inhibited system CI1 (45.6ºC)

11 13 15

3 5 7 9

1 0.00 1.00 Drop 1 2.00 Drop 2 3.00

Time (minutes) Drop 3

Drop 4 4.00 Drop 5 Figure 4: Effect of Inhibition and Temperature on Interfacial Tension

10 12 14 16

2 4 6 8

0 Unhibited CI 1 CI 2 CI 3 Room temperature 46ºC Figure 5: Effect of Inhibition on Contact Angle on a Clean Steel Surface Syringe Water droplet

Figure 2: Typical Interfacial Tension Results for an Uninhibited System Blank oil/brine system (45ºC)

11 13 15

3 5 7 9

1 0.00 1.00 Drop 1 2.00 Drop 2

Time (min) Drop 3

3.00 Drop 4 4.00 Drop 5

Figure 5 is a series of pictures of brine drops on a bare steel surface. Except for inhibitor CI 1, as the corrosion inhibitor was added to the brine, the

82 5.00 Brine + CI 3 – clean surface Brine + CI 5 – clean surface Brine + CI 5 – clean surface

contact angle was lowered. This meant that the droplets were flatter, indicating that the brine had a higher wetting capability when inhibited.

Figure 6 shows the same effect on an iron-sulphide-coated steel surface. Comparing the blank brine contact angle on bare and iron-sulphide-coated steel, the iron sulphide seems to increase the contact angle and therefore makes the surface less water wet. Such behaviour has a positive effect in terms of corrosion tendency. Figure 7 is a summary compilation of the data. It shows the effect of corrosion inhibitors on the wall wettability with brine.

EXPLORATION & PRODUCTION – VOLUME 8 ISSUE 2 surface Steel CI 4 CI 5 5.00

Neat brine – clean surface

Brine + CI 1 – clean surface Brine + CI 2 – clean surface

IFT (mN/m)

Interfacial tension (mN/m)

Interfacial tension nM/n

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