Schlumberger

Case Study: Perforate in Underbalanced Conditions Without Having to Kill the Well

CIRP completion insertion and removal under pressure equipment used to perforate a gross interval of 1,818 ft [554 m]

Challenge: Conduct an extensive perforating operation without having to kill the well and risk formation damage, well control problems, or HSE incidents; conduct a 24-hour well test in the same run.

Solution: Use CIRP completion insertion and removal under pressure equipment to perforate an extremely long interval.

Result: Perforated a gross interval of 1,818 ft [554 m] without formation damage, well control problems, or HSE incidents.

A long underbalanced interval had to be perforated without introducing the risks of a kill operation

Sakhalin Energy Investment Company Ltd. chose Schlumberger to help maximize production from its deviated big-bore gas wells on the Lunskoye-A platform offshore Sakhalin Island. In the first well, LA-517, Sakhalin Energy wanted the entire completion interval to be perforated underbalanced. Not only would this provide a clean path from the reservoir to the wellbore by removing perforating debris, but by removing the perforating guns without killing the well, the perforation tunnels would be protected from potential damage by production-impairing kill fluids.

CIRP equipment was used to conduct a single, extensive perforating operation

To perforate underbalanced without killing the well, a single, long gun string was made up and run into the dead well, then retrieved and broken out under wellhead pressure. Accomplishing that required use of CIRP completion insertion and removal under pressure equipment.

PowerJet deep penetrating shaped charges were selected to maximize productivity; approximately 10,000 charges, spaced at 12 shots per foot (spf), were used to cover the pay zones in the 1,818-ft [554-m] interval that was perforated.

Coiled tubing was used to replace seawater with base oil to create the desired underbalance and to convey the 4.5-in perforating guns to 7,218-ft [2,200-m] maximum depth, where they were fired using dual hydraulic-delay firing heads. To ensure that the guns would survive in this environment with minimal swelling, live tests (confirmed by postjob evaluation) had been conducted at the Schlumberger Reservoir Completions engineering center.

A custom-built, winterized Schlumberger X-11 modular offshore CT unit with active process control and automated safety systems was fitted with 0.145- to 0.190-in wall thickness, 2 3/8-in-OD coil to deploy the guns. CoilCADE coiled tubing design and evaluation software and CoilCAT coiled tubing computer-aided treatment simulations were run in advance, and the model was updated during the runs to account for the actual friction coefficients and forces as wellbore conditions changed.

After firing, then guns were reverse-deployed from the well in 40-ft sections under full well pressure of 2,500 psi [17.24 MPa] as the CIRP connectors were remotely connected and disconnected using the CIRP tool and deployment stack.

The entire interval was perforated without formation damage, well control problems, HSE incidents

Extensive planning by the Sakhalin Energy and Schlumberger teams, along with thorough equipment preparation, enabled a very successful operation. All objectives were met– including prevention of an HSE incidents.

More jobs are planned in the Lunskoye field using CIRP completion insertion and removal under pressure equipment and the X-11CT unit.


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