A coiled tubing string that cannot be pulled is an expensive situation, and the difference between a fishing job and a recovery is usually a joint that was installed for exactly that moment. The hydraulic disconnect sits at the top of the bottomhole assembly and holds the string together until a ball is dropped and pressure is applied. Then it releases, the coil comes out, and the tools below are left with a fishing neck instead of a mystery.
What a Hydraulic Disconnect Does When the BHA Sticks
The tool separates the string from everything below it without moving the pipe. That matters in a horizontal lateral where overpull cannot be transmitted to the stuck point, and it matters in a mill-out where the motor has stalled and the coil is starting to yield. Release is initiated from surface, so the decision is made by the supervisor with the tension and circulation numbers in front of them rather than by the tool failing on its own. Backing off a connection with torque is the alternative, and it leaves a thread profile that is far harder to fish than a GS neck.
Ball Seat, Shear Pins, and Release Pressure
A ball dropped down the coil lands on a seat in the upper sub and converts the seat into a piston. Pressure applied from surface pushes the piston down, shears the pins and drives the slip sleeve out of engagement, and the upper sub separates from the lower assembly. Release pressure is set by the number of shear pins installed, so the same tool can be configured for a shallow vertical well or a deep horizontal one. The pawl detail in the release mechanism resists accidental separation from vibration and torque cycling during normal milling.
Sizes, Bores, and Fishing Necks
The family spans maximum outside diameters from 1.5 to 3.875 inches, bores from 0.438 to 1.875 inches, and balls from 0.5 to 2 inches. Fishing necks are standard GS profiles from 1.5 to 4 inches, which is what the fishing tools on the rig will actually engage. After release, the upper sub, ball seat and ball come back with the coil, and the lower assembly stays in the hole with a known profile rather than a raw break. Outside diameter clearance is checked against the smallest restriction above the tool, since a disconnect that will not pass a nipple is of no use in the lateral.
Hydraulic Disconnect Threads for Coiled Tubing Strings
Top connections cover 1 and 1.5 inches AMMT, 1.90 inches NU, 2-3/8 inches PAC and 2-3/8 or 2-7/8 inches EUE, so the tool can be dressed to match the connector, the motor head or the crossover already in the BHA. The cross-embedded upper and lower subs transmit torque through the joint, which is why the disconnect can sit above a milling motor without becoming the weakest link in the string.
Record the pin count and the expected release pressure in the job program.
Function-test the tool on surface before it goes into the lubricator.
Confirm the GS neck size matches the fishing tools on location.
Testing the Release Before It Is Needed
A disconnect that has never been functioned is an assumption. Bench-test the assembly, verify the ball seals on the seat, and confirm the pump pressure at which the pins shear. On location, check that the ball will pass every restriction above the tool and that the coil is clean enough to deliver it. Most failures are not metallurgical; they are a ball that never reached the seat because a check valve or a nipple stopped it. Ball size and seat size are a matched pair, and substituting a ball on location without checking the seat is the shortest route to a failed release.
The hydraulic disconnect is a small part of the BHA that carries a large share of the risk. Size it to the string, set the pins to the job, and the release becomes a planned operation instead of an accident report.
For more information, please contact China Vigor at info@vigorpetroleum.com or call +0086 29 81161513.
