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Underbalanced perforating is a proven method for achieving optimum perforating tunnel clean-up and well productivity. The Vorwata field has been in production for over a decade, and as such, the reservoir is highly depleted. There are limited options to achieve the required underbalance for perforating and subsequent well start-ups. Traditionally, coiled tubing is used to displace brine in production tubing with nitrogen. However, the remoteness of the asset, combined with complex coiled tubing operations, presents significant challenges.

One alternative is to circulate nitrogen directly into tubing. This displaces the heavier completion fluid, which in turn displaces it through the A-annulus, before setting the production packer. This technique eliminates the need for coiled tubing and, hence, reduces the associated risks and costs. However, other challenges arose: high operating pressure with nitrogen, complicated contingency packer setting, handling of large volumes of nitrogen during bleed-off, and extended exposure of perforating charges at downhole temperatures.

The bp Completions Team systematically addressed these concerns. This was achieved through detailed fluid simulations, review of offset wells, HAZOP studies, and risk assessments. The perforating technique, sequence of operations, and production packer capability are also critical in assessing the best approach. The outcome was safer, eliminating nearly 40 lifts associated with coiled tubing, complex rig-up, and decreased operational risks. It was also more efficient, reducing the completion days to 24 days in the first well and 21 days in the second well, down from 27 days, which was the best performing well before 2023. The average NPT percentage was less than 5%. Finally, streamlined equipment mobilization resulted in significant cost savings.

Removing coiled tubing from the operation resulted in safer operations, improved efficiency, and lower carbon emissions. This nitrogen pumping method has set a new benchmark for future bp Tangguh cased and perforated wells with underbalance shoot-and-drop perforating applications.