Case Study: Simultaneous Underbalanced Perforating Enhances Production

Two zones 200 m apart perforated in one run

Challenge: Perforate two zones that are 200 m apart and have different permeabilities and pressure gradients before running dual completions; minimize damage and obstructions in flow path; prevent crossflow.

Solution: Use PURE perforating system for clean perforations to enable dynamic underbalance to minimize formation damage due to perforation debris.

Result: Maintained ability to retain static overbalance of the wellbore by using dynamic underbalance perforating technology, which ensured no impairment to permeability.

Minimize perforation damage for better connectivity

An operator offshore Malaysia added two wells to its operations in the South China Sea as part of an infill drilling program. The new wells were to produce from two zones, 200 m apart, with 3½-in dual completions. The customer wanted to perforate both zones underbalanced to minimize the formation damage. Perforating the two zones in one run with static underbalance posed a risk for potential crossflow and losses into the more permeable upper zone that could lead to near-wellbore damage and lost returns.

Perforate two zones in a single run

To eliminate the need for an additional run, minimize the risk of perforating both zones with static underbalance, and save rig time, the customer used the PURE system to perforate both zones simultaneously. This method eliminated the need to kill one zone before perforating the other. The PURE system was designed to create dynamic underbalance upon firing while maintaining static overbalance to prevent crossflow between the two zones. Additionally, the dynamic underbalance enabled the removal of debris. The perforating technique also ensured that the upper zone was perforated one minute before the lower zone to prevent gas migration from the lower zone, and perforation tunnels in both zones were cleared of perforation debris.

Execution and results

Both zones were perforated as designed. A tubing-conveyed perforating string with two eFire electronic firing heads was run in hole with a four-pulse firing command applied to activate both firing heads. Both the upper and lower zones were perforated with dynamic underbalance (1,277 psi within 72 ms of perforating and 1,984 psi within 179 ms of perforating, respectively). The technique enabled the test string to be recovered to surface while maintaining the well’s static overbalance condition. Test data revealed negative skin values, validating that the perforating system and technique did not induce any impairment to near-wellbore permeability.

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