FPSO
DC1
DC2
Reservoir Clair Schiehallion Foinaven
Shetland Islands
Orkney Islands
0 0
Scotland km 80 miles 80
< Location of Foinaven eld in the North Sea, West of Shetlands (bottom). Sub- sea production and injection operations are conducted in water depths from 400 to 600 m [1,310 to 1,970 ft] from two drilling centers, DC1 and DC2, each having a gathering manifold and well- cluster arrangement (top). A oating production, storage and offshore load- ing (FPSO) vessel receives the production volumes through exible risers. The Foinaven eld produces from ve Paleocene reservoirs within a faulted anticlinal structure (center).
viscoelastic surfactant (VES) ClearPAC fl uid was selected as the carrier fluid, reducing friction while pumping the gravel-pack slurry, increasing gravel-carrying capacity and minimizing damage to the gravel pack. Schlumberger tested the VES carrying fl uid for compatibility and productivity with the WBM. The treatment incorporated the MudSOLV service to ensure that cleanup would be accomplished while gravel packing. The com- patibility test showed that the ClearPAC fluid maintained its fl uid properties when introduced to the fi ltercake cleanup chemicals and the dis- associated fi ltercake, which was essential for the simultaneous treatment. Moreover, the ClearPAC fluid provided excellent shear-thinning proper- ties to the combined treatment, helping it to fl ow across the troublesome shale sections without causing sloughing. BP fully characterized the reservoir’s grain- size distribution to select the optimal gravel and screen sizes. This study included sieve, laser and scanning electron microscope (SEM) analysis on sidewall cores of the T25 reservoir from a 1994 appraisal well. The company developed an inte- grated model that utilized the three different methods for particle-size determination. The par- ticle-size distribution model was then used to create an artifi cial core pack to test sand reten- tion and define the requirements of both the gravel and screen to be used in the completion. BP selected 30/50-mesh synthetic gravel for its higher permeability and superior performance during corefl ood fi ltercake liftoff tests.31
BP also
decided to run 8-gauge wire-wrapped screens because, unlike the fi ner screens, they retained 96% of the solids and resisted the tendency to plug.
4,500 5,000
1,000 1,500 2,000 2,500 3,000 3,500 4,000
500 0
9:24:43 9:39:48 9:54:53 10:09:58 10:25:03 10:40:09 10:55:15 11:10:29 Time
Pump pressure Pump rate
Moving average pump pressure
0 1 2 3 4 5 6 7
Another crucial aspect of installing this OHGP completion was the need to maintain a continuous overbalanced hydrostatic pressure during the packer-setting process so that the operation experienced no fi ltercake or formation collapse. Schlumberger accomplished this, along with simultaneous fi ltercake-cleanup treatment, using the QUANTUM packer and the horizontal openhole AllPAC screen system.32
The system
worked as designed, maintaining positive pres- sure on the formation and filtercake during the operation (left). The use of effective
, Keeping up the pressure. The plot shows the surface pumping pressure recorded during the installation of the openhole gravel pack in the P110 well. Maintaining positive pressure on the formation and ltercake while pumping was critical to the successful placement of an effective gravel pack. A total of 527 barrels [83.8 m3] of slurry, carrying 100,000 lbm [45,360 kg] of gravel was pumped in less than two hours and resulted in 100% pack ef ciency.
Spring 2004
23
Pressure, psi Start adding gravel
Slurry to screens
Slurry at total depth Stop gravel Start displacement Pump rate, bbl/min
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