Friction pressure in coiled tubing
Particle transport
in the event of lost circulation because of pump failure or excessive fluid leakoff. These safety constraints typically result in multiple sweeps to remove large fi ll volumes.
The real-time PowerCLEAN solids monitor
Solids bed height and dune movement
Jetting and solids mobilization
uses acoustic sensors to detect returning solids at the surface and help determine whether a cleanout is progressing as planned. This non- intrusive monitor mounts on an elbow of the
> Cleaning high-angle and horizontal wells. During CT wellbore cleanouts, ui d is pumped down coiled tubing through a downhole nozzle with jets, or ports. The resulting turbulent ow agitates ll in the wellbore, causing the solids to be mixed and temporarily suspended in cleanout uid as a result of turbulent ow. Pumping rates depend on available horsepower and friction pressure in the coiled tubing. Over time, solids traveling in the coiled tubing- by-wellbore annulus settle on the low side of a wellbore and form dunes behind the nozzle. How far solids can be transported depends on uid properties, particle sizes and density, ow rate and wellbore geometry, including the coiled tubing.
fl owback line. The PowerCLEAN system recently played a key role in wellbore-cleanout operations in continental Europe and the Gulf of Mexico. After hydraulically fracturing a gas well com- pleted with a 7-in. liner, the operator needed to clean out the wellbore at balanced pressure con- ditions to avoid damaging the well. A 59-bbl [9.4-m3] volume of bauxite proppant filled the wellbore from about 13,700 to 16,400 ft [4,176 to 4,999 m], a length of 2,700 ft [823 m]. The maximum well inclination at this depth was 31° and the bottomhole temperature (BHT) was 304° F [151° C]. A 13
⁄ 4 -in. coiled tubing string pumping the
new cleanout fl uid penetrated fi ll at about 6 to 10 ft/min [1.8 to 3 m/min]. The PowerCLEAN software predicted that other fluids would not provide an effective cleanout because of the high BHT and large casing. It also deter- mined that several sweeps would be required to remove solids that settled in high-angle wellbore sections. Each CT penetration into the fi ll was limited
to 80 ft [24 m], which minimized the solids dune height and prevented coiled tubing from becoming stuck if fl uid loss occurred or pumping stopped. Sweep speed while pulling out of the well was 10 to 20 ft/min [3 to 6 m/min] to ensure complete fi ll removal. An optimal flow rate through the 21,000 ft
> Integrated wellbore cleanout services. In addition to enhanced design software, new cleanout uids and solids monitoring at the surface, the PowerCLEAN system includes a specialized nozzle that creates a uid vortex, which removes solids at lower ow rates than conventional nozzles. Unlike other nozzles, PowerCLEAN nozzles use optimized jet angles to produce this swirling effect, and have no moving parts to maintain. The new PowerCLEAN uid and nozzle effectively remove ll at rates as low as 1 bbl/min [0.15 m3/min] for 7-in. casing and 2 bbl/min [0.3 m3/min] for 95 casing at any inclination.
8 -in.
speed when penetrating fi ll, particle-bed depth, CT pulling speed for sweeping solids uphole, and number and length of sweep before running back in. The software accounts for factors such as maximum surface pressure and pump rate, acceptable bottomhole pressure (BHP), entrained solids concentration, fluid leakoff or infl ow and solids transport.
Additional constraints ensure safe, problem- free cleanouts. The solids bed is not allowed to exceed a specifi ed height that avoids drag on the coiled tubing, higher friction pressures and stuck pipe. In addition, the volume of solids that can be lifted above the nozzle is limited. This helps ensure that the coiled tubing can be pulled out
-in. liner and had a complex trajectory with a maximum deviation of 70° . At a BHT of less than 200° F [93° C] and a 0.75-bbl/min [0.12 m3/min] pump rate, the PowerCLEAN nozzle with a xanthan-base fluid resulted in an optimized cleanout.
⁄ 2
[6,401 m] of coiled tubing was achieved at pres- sures below 4,000 psi [27.6 MPa] because of the low-friction PowerCLEAN fluid. Solids returns were monitored at the surface in real time. The well was cleaned without problems and 59 bbl of bauxite proppant were recovered. In another well, the PowerCLEAN service was used to remove excess bauxite from a Gulf of Mexico well in order to replace the gravel-pack screen assembly. This wellbore was completed with a 31
Spring 2004
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