Packer Set, Annulus Pressure Creep, and Tubing Pressure Test
An operator is completing a well with 7-in, 29 lb/ft casing and 3½-in, 9.3 lb/ft N-80 tubing. The hydraulic-set retrievable packer is at 2,900 m TVD (3,050 m MD), with perforations at 2,850 m TVD. The well is filled with 8.6 ppg filtered brine, and the reservoir pressure is 1,380 psi. The packer is rated for 7,500 psi differential. You set the packer with 2,200 psi tubing pressure, then bleed the tubing to zero. The annulus gauge reads 180 psi and climbs slowly to 320 psi over 10 minutes; tubing pressure stays at zero. The plan is to pressure-test the tubing to 3,000 psi against the packer. The annulus is closed, and no annular fluid has been added or bled since the packer was set. There is no recorded annulus pressure before setting.
1. Calculate the hydrostatic pressure at the packer and the overbalance against the reservoir. Does the packer's 7,500 psi differential rating cover the planned 3,000 psi tubing test?
Read the worked answer
Convert depth to feet: 2,900 m × 3.2808 = 9,514 ft.
Hydrostatic = 8.6 ppg × 0.052 × 9,514 ft = 4,254 psi.
Overbalance = 4,254 − 1,380 = 2,874 psi. The well is safely overbalanced with 8.6 ppg brine.
During the test, tubing pressure is 3,000 psi and annulus pressure is near zero, so the packer sees about 3,000 psi differential. That is well below the 7,500 psi rating. The rating is adequate, but the annulus pressure must be monitored because any trapped annulus pressure reduces the differential while a leak path can change it rapidly.
2. What are the possible causes of the annulus pressure rise, and what would you do before starting the tubing pressure test?
Read the worked answer
The annulus is closed and the tubing is at zero, so a simple packer leak from annulus to tubing would normally bleed annulus pressure down, not up. The rise is more consistent with thermal expansion of trapped annulus fluid as the well warms after setting, or with a small leak from a trapped volume into the annulus. A 140 psi rise in 10 minutes is not automatically a failure, but it is not a stable baseline.
Before testing:
- Monitor the annulus for at least 30 minutes and record whether the pressure stabilises.
- If it continues to climb, bleed a small volume and watch the response; a rapid rebuild suggests a leak source, while a slow fall suggests thermal effects.
- Do not start the 3,000 psi test until the annulus is stable or the source is understood.
- Record the stable annulus pressure and include it in the test procedure so the packer differential is calculated correctly.
3. During the test, tubing pressure reaches 3,000 psi and holds for 5 minutes, then falls 150 psi while annulus pressure rises 200 psi. What does this indicate and what should you do?
Read the worked answer
A tubing pressure fall accompanied by an annulus pressure rise indicates communication from tubing to annulus. A 150 psi drop is only 5% of 3,000 psi, but the simultaneous annulus rise confirms a leak path rather than thermal decay or gauge error. Likely paths are the packer seal, a tubing connection above the packer, or a pinhole in the tubing.
Actions:
- Stop the test and bleed tubing pressure in a controlled manner.
- Check surface connections and the test cap first; a surface leak can mimic a downhole failure.
- If surface equipment is sound, isolate and retest the packer/tubing. Do not proceed with completion operations until the leak is found and repaired.
- If the leak is downhole, unset the packer and inspect/replace the seal assembly or tubing joint.