A water injection well offshore UK was undergoing a start-up procedure when a build-up in wellhead pressure was observed indicating a possible blockage by a hydrate plug. Attempts to inject methanol through the injection master valve cleared the hydrate present between the flow valve and the wing valve. However, the hydrate was still confirmed as being present below the subsea tree, but the length was unknown.
The primary solution for removing the remaining hydrate was pipe pulse pressure technology with Welltec’s e-line solution as a contingency that could be carried out through a RLWI vessel.
After much consideration, the Welltec® Reverse Circulating Bit (RCB) for milling solutions was selected over any induced heat solution as it was thought to be less likely to generate rapid gas release from the hydrate allowing for a more controlled environment.
After three days of sending pulses to break down the hydrates with no visible results, Welltec’s solution was rigged up. The scope of work was to restore injectivity and access through the wellbore by removing the hydrate.
The first toolstring consisted of a Welltec Release Device® 218, Well Tractor® 318 and a RCB 312 fitted with a 3.8” milling bit. The hydrate was tagged at 1,815 ft (553m) where the RCB was activated and milled down to 1,844 ft (562m).
A decision was then taken to remove the 3.5” stand-offs and run with the larger 4.2” mill bit in order to reduce the risk of sticking by creating a slicker tool. This solution effectively milled down to 1,997 ft (608m) when the operation was suspended due to adverse weather conditions.
This was the world’s first milling of hydrate on e-line, proving yet another application of Welltec’s unique milling and cleaning solutions.
This capability has widespread application for operators around the world as a remedial approach for this complex problem. In less than 20 hours of actual milling time 173 ft (52m) of hydrates were removed to a depth that allowed the client to re-establish functionality to the downhole safety valve.
In less than 20 hours of actual milling time 173 ft (52 m) of hydrates were removed to a depth that allowed the client to re-establish functionality to the downhole safety valve.
