Rigless Thru-Tubing Gas Lift Retrofit System Optimizes Production in Shut-In Well by Deepening Injection Point Below Production Packer

Abstract

Well A, a Brownfield offshore oil producer in Brunei, was shut in due to multiple leaks in the tubing. The well was drilled in 2000, so was facing common issues associated with depletion prior to shut-in. Production from the well was restored by installing an innovative thru-tubing retrofit gas lift system, allowing for injection of lift gas below the production packer, while simultaneously restoring tubing integrity by isolating the leaks.

The goal of the rigless intervention was to restore tubing integrity by installing an ISO 14310 V0-validated gas-tight straddle across the leaks. The straddle also serves as a retrofit gas lift system, enabling delivery of lift gas below the production packer, just above the horizontal open hole gravel pack section. The straddle directs lift gas down an inner string hung from the lower packer with an installed gas lift mandrel on the bottom of the tail pipe, delivering lift gas below the production packer. The straddle features internal flow paths, allowing produced fluid to flow through the straddle back towards surface.

Once installation was complete, the new gas lift valve was installed 200 m TVD (true vertical depth) deeper than the lowermost side pocket mandrel. During the initial well test, lift gas was injected down the casing and entered the production tubing through the leak points and SPM, which were contained within the straddle assembly. The upper and lower packing elements in the straddle directed all gas through the crossflow sub and into the inner string suspended from the lower packer. A slim gas lift valve was connected to the downhole end of the tail pipe. By injecting lift gas in the lower completion, hydrocarbon was unloaded from a deeper depth than would have been possible using conventional gas lift. Within four hours of starting lift gas injection, Well A was flowing steadily with 900 kPa of flowing wellhead pressure (FWHP). The well was then shut in, pending a full well test.

This novel approach helped avoid an expensive workover and minimized runs in hole by incorporating the gas lift retrofit system into the straddle isolating the tubing leaks. This installation was the first in Brunei that placed the lift gas injection point beyond the production tubing in a horizontal well. As a result, a well that had been shut in for five years was re-instated and production was further optimized by deepening the lift gas injection point 200 m TVD below the lowermost side pocket mandrel.