For this system, an atmospheric chamber is run into the well with the
gun assembly. To remove the risk of sanding in the gun string, the atmospheric
chamber is activated with the guns clear of the zone after perforating in an
overbalanced condition. The perforated interval is then exposed to a short,
sharp pressure drop, creating a differential pressure and an underbalanced
state across the perforations. This drop in pressure draws a controlled volume
of fluid into the wellbore, breaking down a hemispherical region at the
entrance of each perforation and pulling perforation debris and mud from the
invaded zone into the crushed region. The initial drop in pressure is followed
by a controlled flow into the chamber that pulls the loose sand and debris from
the collapsed region through the casing cement tunnel into the wellbore. The
dynamic pressure drop created by this downhole surge allows uniform cleanup of
the perforations over the entire interval.
During the perforation prepacking process, gravel slugs are pumped in a
non damaging carrier fluid. This fluid is a viscoelastic surfactant,
which—because of its viscosity and gravel suspension
capability—ensures that the gravel enters and packs the perforations
efficiently. The gravel slugs are separated with alternating stages of acid and
spacer to further improve the cleanup and perforation packing efficiency.
Four multizone wells underwent the perforating and gravel-packing
operation, all under slightly different conditions and with slightly different
variations in sequencing of the surging and perforating.
Surging and perforation prepacking improve skin factor and well
The results clearly showed that dynamically surging the perforations,
immediately followed by prepacking, greatly improved the packing efficiency of
the perforations. This combining of the two processes—a departure from
the standard operation in which the two are handled independently—greatly
increased the packing efficiency in the perforation tunnels, reduced skin,
improved reservoir connectivity, and enhanced well performance. Perforation
packing factors improved from 10 lbm to 40 lbm of gravel per foot of
perforation. Sand-free production as achieved, with a reduced drawdown across
the sandface. Production reached rates as high as 5,000 bbl/d.
The Transcend* family of openhole sand management services includes screens and injection and inflow control devices, AquaPac* integrated water packing technologies, OptiPac* Alternate Path† gravel-pack systems, and IntelliPac* measurements in real time.