Case Study: Modified Gun String Design Reduces Permanent Packer Axial Load by Half

Perforating-shock modeling optimizes configuration and mitigates risk of packer failure

Challenge: Determine the maximum perforation force possible for a gun string used during a downhole permanent completion while minimizing the risk of damaging permanent packer or any other downhole equipment.

Solution: Use perforating-shock modeling to compute axial load on permanent packer and downhole equipment; design gun system to reduce shock during perforating in overbalanced, underbalanced, and dynamic underbalanced conditions.

Result: Perforated well with reduced axial load, resulting in production increasing to 2,200 bbl/d versus an expected 700 bbl/d.

Perforate offshore while mitigating packer damage

An operator sought to maximize well production by perforating one of its reservoirs located in an offshore field in the Far East. The operator needed a way to perforate with the greatest possible penetration, but it was also important to mitigate the risk of damage to the string’s permanent packer and equipment downhole.

Reduce risk with downhole shock model

After comprehensive consultation with the operator regarding its production goals, Schlumberger used a perforating-shock planning system to predict the maximum force from a perforation-induced pressure wave and to design a perforating string to minimize the shock. This planner considers the reservoir and completion details to compute the axial load on downhole equipment while perforating. The shock planner computed that the axial load on the packer could reach a maximum of 127,000 lbf.

Based on this prediction, the operator selected a more robust permanent packer to withstand the shock during perforating, and Schlumberger redesigned the gun string to include one 20-ft chamber above and one 20-ft chamber below the packer to reduce shock. Schlumberger ran its SXAR explosive automatic gun release with hydraulic-delay firing heads and a long-slot debris-circulating sub below the completion string. The reservoir was then perforated using PowerJet Omega deep penetrating shaped charges and the PURE perforating system for clean perforations.

Exceed production estimates with enhanced gun string

The redesigned string was more robust and could withstand higher pressure and greater perforating charges. With the new, robust string design, reservoir production increased to 2,200 bbl/d, far exceeding the expected rate of 700 bbl/d.

Download: Modified Gun String Design Reduces Permanent Packer Axial Load by Half (0.15 MB PDF)

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