Case Study: Highly Deviated, Thinly Laminated Deepwater Well Perforated with Precision

Schlumberger applied an oriented system for successful underbalanced perforating of injector wells

Challenge: Perform underbalanced perforating of a long, thinly laminated section in a deviated deepwater well. Highly accurate orientation was required to perforate only the productive zones and to ensure sand control.

Solution: Combine the oriented tubing-conveyed perforating system and the PURE clean perforations system to deliver highly accurate orientation, unconventional phasing, and dynamic underbalanced perforating.

Result: Fired guns accurately on 90°/270° phasing; confirmed dynamic underbalance of more than 3,000 psi from the fast pressure gauge and minimal skin from subsequent testing.

Perforate a long deviated well section in a thinly laminated reservoir

Deepwater operations offshore Malaysia were faced with a thinly laminated reservoir that has relatively unconsolidated and poorly sorted sandstone intervals varying in length from 330 ft to 1,650 ft [100 m to 500 m] with modest unconfined compressive strength of 900 psi. The risk of sand production using conventional perforating was high. Many of the sand layers are just over 3-ft [1-m] thick and are located in a well section that has deviation in excess of 80°.

Oriented perforating was the best solution for low-debris perforating in the highly deviated well, but conventional 0°/180° phasing had high potential for penetrating the shale layers and water zones separating the sandstone layers.

Schlumberger determined that it would be necessary to use a perforating system that would enable

  • use of a long, heavy, oriented gun string
  • optimized oriented perforating for sand control
  • verification of orientation ±15° before perforating and confirmation ±1° after gun retrieval
  • minimal perforation damage.

Combine highly accurate orientation, unconventional phasing, pressure-activated gun firing, and dynamic underbalance perforating

The Schlumberger Reservoir Completions Center in Rosharon, Texas, USA, provided the solution by engineering a highly accurate 7-in orientated tubing-conveyed perforating system with 90°/270° phasing and combining it with the PURE clean perforations system. The combination of confirmed orientation accuracy, 90°/270° phasing, and dynamic underbalance perforating enhanced production from each perforation tunnel and helped maintain the stability of the formation.

The gun system was designed to provide an orientation accuracy of ±15°, and it incorporated the high-precision OCD orientation confirmation device, which provided verification of perforation tunnel orientation ±1° upon retrieval of the gun string. Equipped with passive orienting weights, the system was configurable in individual sections of over 1,000 ft [300 m] connected by roller-bearing swivels.

The 90°/270° phasing enabled perforation parallel with the reservoir layers, without damaging the sealing shales or penetrating the water zones.

Deep-penetrating HyperJet perforating charges, without plastic jackets, provided 8-spf shot density and minimized debris in the injection wells.

These system component features contributed to the solution:

  • The orientation minimized tunnel diameter in the formation, thereby increasing the strength and number of effective perforating tunnels. It reduced the pressure differential across perforated intervals, injection rate per perforation, and sand production.
  • Unlike conventional perforating, which relies on a large static pressure differential between the wellbore and the formation to remove perforation debris, the PURE system technique fully exploited the pressure transients that occurred immediately after perforating.
  • HyperJet charges minimized perforation damage and enhanced stability during drawdown and depletion.

Deliver clean perforations and minimal skin through accurately oriented, underbalance perforating

The OCD device showed that the guns were fired accurately on 90°/270° phasing, and data from the fast pressure gauge confirmed that a dynamic underbalance of more than 3,000 psi was reached while near-balance conditions were maintained. Those accomplishments contributed to creating perforation tunnels that were clean and stable.

Testing after completion confirmed the flow rate expected based on the presence of minimal skin following the underbalance perforation.

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