Successful high backpressure pigging in ultra-deep-water using Coiled Tubing downline

By Halliburton

Rodrigo Gianni Ferrira

As part of the pre-commissioning activities in a deep-water offshore field in Brazil, eight FCG (flooding, cleaning and gauging) operations were required on production, gas injection and gas lift pipelines of various diameters and lengths (up to 10” diameter and 23 Km long) to fill, clean and confirm pipeline geometry in preparation for the next pre-commissioning steps. The pipelines are constructed using CRA (corrosion resistant alloy) and hence, had to be flooded with clean freshwater to avoid corrosion due to ingress of salt and ferrous metal particles. The operations were performed by pumping fresh water from a CSV (Construction Support Vessel) using a specially designed CRA coiled tubing string to reach 2100 meters water depth and powerful diesel driven pumps to ensure the high flowrates and pressures required.

Challenges

• Deliver clean freshwater into pipelines at 2100 meters water depth
• High flowrates needed to keep minimum pigging speed
• High friction head loss on the long downline
• Large quantity of freshwater required: more than CSV capacity
• SIMOPS with a second vessel to store and supply freshwater

Solutions

• CT (Coiled Tubing) as a downline.
• CRA CT eliminated corrosion, avoided cleaning / pickling of CT and reduced friction.
• 550 Bar working pressure CT: to achieve required flow.
• High pressure HT-400 pumps on small footprint.
• Integration of water supply vessel and clear communication process

Results

• All eight FCGs successfully performed
• 130 hours of continuous safe operation
• 20 hours of pumping at 200 Bar and average 900 liters per minute
• Over 77 hours saved due to CRA CT reduced friction pressure / higher flow

Through collaboration with the customer, a safe, efficient and environmentally responsible solution was engineered and delivered to meet the project requirements

Figure 1: CRA CT string

Figure 2: Operational layout