A Orientation mark in degrees
to establish perforation depth, thus eliminating the need for a second coiled tubing reel, saving time, improving effi ciency and providing a safer work environment.
Statoil and Schlumberger engineers opti- B Pin set at 0° Detonation cord (green) Detonation cord port Pendulum assembly Bullet tube CD
> Con rming orientation. The OCD device was developed by Schlumberger to con rm performance of the OrientXact perforating system. Photograph B shows the OCD device installed in the carrier assembly with the detonation cord (green) passing through the OCD cell. In photograph D, the OCD device (C) has been opened. Shown is the internal pendulum assembly consisting of a freely rotating collar, bullet and barrel tube assembly through which the detonation cord passes. When the perforating guns are red, energy emitted from the detonation cord forces a bullet inside the barrel tube toward the inside wall of the OCD device. On detonation, the bullet simultaneously marks the exact gun orientation relative to vertical— 0° orientation is shown in A. The OCD unit measures perforation orientation with an accuracy of ± 0.5° .
mized operations by integrating multiple technologies. The OrientXact self-orienting gun system provided accurately aligned perforations. Pulse-telemetry through the wellbore fluid col- umn transmitted real-time depth correlation data to the perforating team. PowerJet Plus charges deeply penetrated the reservoir leaving minimal gun debris in the casing. With the well still under production pressure, PURE tech- niques provided dynamic underbalance, minimizing perforation-tunnel skin effects and assisting in crushed formation debris removal. The eFire-CT electronic firing head for coiled tubing deployment addressed safety concerns by requiring a coded sequence of coiled tubing pump-rate changes while downhole to detonate the perforating guns. With the eFire-CT system, safety spacers are not required, allowing use of longer gun lengths.14 A total of 10 coiled-tubing perforating runs were performed in the three wells with guns ranging in length from 50 to 100 m [164 to 328 ft]. Engineers using DepthLOG correlations and universal tubing length monitor (UTLM) placed the perforating guns with an accuracy of ± 1 m [± 3.3 ft] at a depth of 4,500 m [14,764 ft] on all perforating runs. All guns properly deto- nated on target. Ultimately, the OCD unit confi rmed the perfo- rations at +8, +4 and +3° on three separate perforating runs. The linking of interdependent perforating technologies in the Gullfaks field improved operational efficiency and optimized production rates.
from optimum perforation angle (above). Down- hole pressure gauges indicated an instantaneous underbalance of 250 bar [3,626 psi] generated within 0.1 s of detonation. The linking of interdependent technologies to
address formation damage, depth of charge pen- etration, charge chemistry, detonation debris and the perforating environment in the Visund
fi eld minimized sand production and resulted in a three- to sixfold production increase over that achieved with previous perforating practices.
14. Safety spacers are placed between the gun assembly and the ring head. This allows live guns to be loaded into or pulled from the hole, exposing personnel to only the ring head while explosive charges remain below the rig oor.
Improving Efficiency in a Gullfaks Satellite Field To improve production rates in a Gullfaks satel- lite field, Statoil reperforated three wells. Operations took place with the wellheads under pressure. Engineers recognized that sand cleanout operations might be necessary prior to reperforation. Typically, two coiled tubing reels would be required, one for sand cleanout and the other confi gured with an electric wireline used for accurate perforation-depth correlation. Engi- neers combined conventional coiled tubing with a real-time DepthLOG CT depth correlation log
Avoiding Sand in the Rimfaks Field Avoiding sand production in Statoil’s Rimfaks development is key to optimizing well produc- tivity. Another satellite of the Gullfaks field, Rimfaks is located in the northern part of the Norwegian North Sea. The I-3H well produces from weak sandstone reservoirs that require per- forating near the direction of maximum stress to minimize excessive sand production. Downhole
fl ow-control hardware, including chokes, packers and associated equipment are used to control production rates across the multizone comple- tion. Sand fl ow and postperforation debris must be avoided to prevent damage and erosion of the complex completion assembly.
36
Oilfi eld Review
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