Marie Morkved shows how a desire to eschew ‘how we’ve always done it’ helped Maersk Oil take a different approach to well intervention – using coiled hose on its UK North Sea Balloch field.
Coilhose being deployed via the moon pool on board the LWIV during well operations.Photos from Maersk Oil.
The Balloch field came onstream in May 2013, with three wells: P17, P18 and P20. Balloch produces through the Global Producer III (GPIII) in Quad 15 of the UK North Sea. The field has exceeded expectations and has delivered a significant amount of GPIII’s production. However, in 2016, we saw a decline in one of the wells, P18. To maximize economic recovery and deliver value for our business, we had to brainstorm ideas to sustain as many barrels as possible.
The subsurface team considered several possible reasons for P18’s production decline, including eroded screens, collapsed screens, formation collapse and screen plugging. The well has a downhole gauge so reservoir pressure decline could be ruled out.
In the end, the most likely problem appeared to be screen plugging. The sand is very clean, but we experienced losses when drilling into the Devonian formation just below the reservoir sand. The first Balloch well drilled into the Devonian without problems, but in P18 it resulted in a number of barrels of mud being lost, which required us to pump plugging material (LCM) as a control measure. This also resulted in a very basic clean-up of the well before the screens were run, and it was considered likely that there was still some plugging material remaining. This material could plug the screens, resulting in decline in production over time.
The upshot was that these sand screens needed to be cleaned. We believed we could do that by pumping a cleaning fluid across them to dissolve the residue that was blocking them. But, we needed to act quickly, and the go-to method of using a semisubmersible drilling rig with coiled tubing to carry out this intervention work was going to take too long to mobilize and get on location. We needed to think differently.
Ultimately, we chose to use a light well intervention vessel (LWIV) – the Well Enhancer – and a 19mm outer diameter coilhose from Quality Intervention. The coilhose is as thick and light as a garden hose. However it’s very strong (four times the yield strength of slick line) and capable of pumping at pressures of up to 50,000psi and at the depth we required – 9300ft (2834m).
It doesn’t require the heavy equipment that coiled tubing does, and it could be used on a LWIV, which could be in the well within 36 hours during the winter months, which was critical for us. However, nobody had ever done this before – either in a subsea well or deeper than 2000ft (609m).
Coilhose being deployed on board the LWIV.
One of the key components in this project was the creation of a subsea stripper– a new piece of kit created for this project. It is essentially housing for rubber packings that seal around the hose. If it was too tight, the hose wouldn’t move. If it was too loose, we may risk spilling oil to sea. It was vital that it was tested thoroughly, first in a test well in Norway and then yard tested in the UK.
We also needed to test the last line of defense: a shear seal – a massive 7in valve that will cut whatever is in the hole and seal off the wellbore. The idea that the shear seal would not cut the tiny hose was almost unthinkable, but we couldn’t leave that to chance. We sent the hose to Houston to be tested with the shear seal. It passed.
A special nozzle was built for the hose to jet the cleaning fluid on to the screens. We tested the hose using different types of acid: formic acid and citric acid. We cooked the hose in different strengths of the acid to check what would happen to it under those conditions. We were able to see that the hose performed well with 20% formic acid.
The result was a world first – the use of a LWIV and coilhose at depths of 9300ft (2834m) to perform a well intervention at around 30% cheaper than traditional methods. Our ultimate aim was to clean the sand screens and get the well flowing better and we achieved that.
While we were able to almost double production from P18 post start-up, the big success is the testing and trialing of this way of performing a well intervention. We’re looking at using a LWIV for more well interventions this year.
Marie Morkved is head of Production Technology for Maersk Oil UK. Marie has more than 20 years’ oilfield experience including seven years with Schlumberger and 10 years with BP. She joined Maersk Oil in 2011. Marie has an MSc in mechanical engineering from NTH Norway and an MSc in petroleum engineering from Imperial College London. Throughout her career, she has worked on well interventions and well and reservoir management in Germany, Holland, UK, Norway, Egypt, Denmark and Azerbaijan.