June 30, 2017

Problem Statement

The production from a subsea well went into severe decline and it was thought that the well’s sand screens needed to be urgently cleaned. The standard solution would have been to use a semi-submersible drilling rig with coiled tubing, but this is both expensive and slow. So, a new solution had to be explored and developed.

Aim

Find a cheaper and faster alternative to using a semi-submersible drilling rig to clean a subsea well’s sand screens and improve the well’s production.

Method

Formic acid was chosen to clean the screens.

To get the fluid down to the formation (a depth of 9,300 ft) it was decided to use a coil hose deployed from a light well intervention vessel (LWIV).

A LWIV is a smaller, more manoeuvrable mono-hulled ship. It’s often used for subsea well interventions but using wireline (electric cable) or slick line (thin wire).

Coil hose is very different from coiled tubing in that it can be rigged up using slick line equipment, still allowing pumping to take place.

10,000ft of coil hose with an outside diameter of 19mm needed to be deployed – the size of the hose meant that the pump rate would be low.

To tackle this, several new pieces of hardware had to be designed, manufactured and tested. Numerous programmes and safety reviews were also carried out.

Impact

The intervention was completed incident free and initially the well production rate doubled.

This successful result confirmed our hypothesis that the decline was due to screen plugging. This is useful learning for the future.

The intervention saw three world firsts:

  • The first time coil hose had been run from a light well intervention vessel;
  • The first time coil hose had been run into a subsea well; and
  • previously nobody had run coil hose deeper than 2,000 feet – we ran it to 9,300 feet.

Overall timing from concept creation to execution was just four months – a significant reduction compared to the alternative method of using a semi-submersible rig.

The success of this job has allowed us to look at other candidates for cost-effective well intervention to improve production.

Reduced project timeline: Total project timeline was 4 months, compared to 6-8 months needed for semi-sub intervention (inc. contract)

Total savings anticipated: Around 30% saving – compared to the alternative solution of using a semi-sub rig and coiled