A deepwater, offshore well was experiencing high gas-oil-ratio (GOR) caused by coning and breakthrough of re-injected gas. The temporary solution for the operator until a permanent solution could be found was to cycle the well production on and off allowing the reservoir to resaturate with oil while shut-in, and then reopen oil flow to the FPSO until the GOR became unacceptably high for the facilities. This resulted in significant decreased production for the well over time. Diagnostic surveys revealed the high gas entry was coming in from the top of the open hole gravel pack completion.

The operator, working with multiple service companies, engineered a gas shutoff solution to lower the GOR, increase production and recover additional reserves. The agreed upon design would require installation of a 525 ft (160 m) long, retrievable straddle isolation assembly. Installation and assembly of this straddle necessitated accurate depth control and “force-with-finesse” during installation; the former to ensure proper position; the latter to avoid seal damage whilst stabbing and latching the segments in, joint by joint.

Welltec’s combination of Well Tractor® and Well Stroker offered the best solution for the operator as it can exert the required force downhole at exact depth, hence the Well Stroker was a better option than CT for this operation, as CT exerts the force all the way from surface losing the required finesse.

An e-line drift run was conducted first to the required setting depth with the Well Tractor acting as tool weight. On the second run, the lower packer was run with the Well Tractor and set. The next run was the first joint of the assembly and the Well Tractor was run to ensure the toolstring was seated into position and to compress the stroker piston.

The Well Stroker was required to stroke down and ensure the RS2 latch had been fully seated and then to shear the GS running tool pin to release the Well Tractor/Well Stroker toolstring from the assembly. The subsequent runs involved conveying and stroking the various joints and packers into position, resulting in an entire assembly; sixteen runs in all were required to install the straddle assembly.

The job was completed without any nonproductive time or lost time incidents and in 15 days, 30 days sooner than the planned 45 days the operator expected the job to take.

This was the first operation of its kind offshore West Africa. As a result of the intervention, gas breakthrough was shut-off and oil production increased multifold.