Wireline lubricator length and pressure testing on a live well
A wireline crew is preparing to run a 7.5 ft perforating gun into a live well with 3,200 psi shut-in tubing pressure. The lubricator is 12 ft long and rated 10,000 psi. The wireline BOP stack has pipe rams, blind rams and a shear/seal ram. The grease injection head is rated 10,000 psi, and the stuffing box has new packing. The well has 4½-in tubing and 7-in casing; the master valve is 4½-in, 5,000 psi. The toolstring includes a 2 ft spacer and a 1.5 ft firing head. A rope socket and weak point add about 0.8 ft. The crew plans to pressure-test the lubricator with the gun already inside, then equalise and open the master valve. The wireline unit has 0.108-in slickline. The well is on a small platform with limited deck space.
1. Check whether the 12 ft lubricator can safely contain the toolstring. Show the length calculation.
Read the worked answer
Toolstring length = 7.5 ft gun + 2 ft spacer + 1.5 ft firing head + 0.8 ft rope socket and weak point = 11.8 ft.
A 12 ft lubricator leaves only 0.2 ft, or about 2.4 in, of clearance. That is not enough for safe wireline operations. The tool must be pulled entirely above the blind rams so the rams can be closed, and the crew also needs room for the wireline clamp, the rope socket and any movement during pressure equalisation. With only 2.4 in spare, the tool could be across the rams or the rope socket could be too close to the stuffing box. The safe decision is to use a longer lubricator or to break the toolstring down into shorter sections. The crew should not open the well on the basis that 12 ft is greater than 11.8 ft; the margin must be practical, not theoretical.
2. Give the correct sequence to pressure-test, equalise and open the well.
Read the worked answer
First, make up the toolstring and lubricator with the correct BOP configuration and close the blind rams below the lubricator. Fill the lubricator with water and pressure-test it to at least the maximum anticipated surface pressure, normally the wellhead shut-in pressure plus a margin, and in this case not less than 3,200 psi; the 5,000 psi master-valve rating may set the test ceiling. Hold the test for the required period and check the grease head, stuffing box and all connections. Bleed the test pressure, then equalise the lubricator pressure with the wellhead pressure through the equalising valve. Open the master valve only after the pressures are equal. Then open the blind rams and run the tool in slowly, monitoring the stuffing box and grease injection. If a leak appears at any stage, stop and close the BOP.
3. During the run, grease injection pressure cannot hold the seal. What should the crew do?
Read the worked answer
Stop the run immediately. Loss of grease injection means the wireline seal is not reliable, and well pressure could reach the stuffing box or the deck. The crew should stop movement, close the wireline BOP pipe rams or blind/shear rams as appropriate to the tool position, and bleed pressure from the lubricator before repairing the grease head or packing. They must not continue running or pulling while the seal is failing. The tool position matters: if the tool is across the rams, shear rams may be needed, but that risks losing the tool in the well. The supervisor should confirm the tool is above the rams before closing them and should check grease supply, injection pressure and packing condition. The well should remain shut in until the pressure-control equipment is restored and re-tested.