Published: 12/01/2011
Published: 12/01/2011
Operators working in the Middle East have found that their gas production wells are vulnerable to hard scale deposits, consisting of various forms of FeS. The collection of these deposits on the walls of production tubing forms an ever increasing restriction that results in declining production rates.
Finding an efficient method to remove scale deposits from production tubing and liners, to regain well access for further stimulation, has often eluded operators. Restrictions in the ID of the tubing string above the cleanout zone limit the mill cleanout size. When used in combination with positive displacement motors, low ROP, short mill life, and blockage of the tubing perforations with larger cuttings have been observed. Plugged perforations or formation damage has also been seen when using dissolving chemicals for the cleanout.
An operator whose well lost its production capability, due to heavily scaled completion tubing, requested a solution. Hard scale is best drilled at high speed and with a non-agressive mill. For this reason, the suggested solution was to drill a pilot hole with the 2 7/8-in Neyrfor TTT turbomill in combination with a 3 1/2-in Schlumberger D2 tungsten carbide insert mill to initiate de-scaling operations, generating up to 2400 rpm and 60 hp. The combination of the Neyrfor TTT turbodrill and the TT Turbomill enables efficient milling rates in high-pressure, high-temperature (HPHT), underbalanced drilling (UBD), and when specialty fluids are present.
To remove the remaining scale from the completion tubing walls and profiles, a Scale Blaster cleanout was performed with a 2 7/8-in Jet Blaster tool system and 6,250 bbl of Sterling Beads slurry on a second run. Scale Blaster is a proven, non-damaging cleanout technique for hardest inert scale deposits. It combines high efficiency jetting performance of Jet Blaster systems with Sterling Beads, an artificial blasting material that breaks scale on impact, however is non-damaging to steel tubular and completion. Being based on the jetting principle, Scale Blaster cleanouts are not limited by tool OD or completion restrictions.
The scale cleanout operation was performed on 2 3/8-in coiled tubing. After dry tagging the top of the scale, the 2 7/8-in Neyrfor TTT cleanout was conducted with good progress: advancing the coil at 8 ft/min. The 3 1/2-in pilot hole was cleaned to the bottom of the production tubing in a single run. On the second run, the Jet Blaster tool with Sterling Beads removal system completely cleared the 4 1/2-in tubing of heavy FeS deposits at a rate of 2.6 ft/min. The two run solution with the Neyrfor TTT turbodrill and Scale Blaster service efficiently removed the FeS scale by reducing it to powder cuttings, which were easily lifted from the wellbore with slick water.
Challenge: Remove hard iron sulfide (FeS) deposits from 5,860 ft of heavily scaled 4 1/2-in production tubing to restore production and wellbore access.
Solution: Run a 2 7/8-in Neyrfor TTT thru-tubing turbodrill system with a D2 TT Turbomill thru-tubing mill to make a pilot hole and perform a Scale Blaster cleanout run with a 2 7/8-in Jet Blaster tool system and non-damaging Sterling Beads to remove remaining scale from the tubing wall on a second run.
Results: On the first run, the Neyrfor TTT turbodrill successfully drilled through 5,860 ft of heavily scaled production tubing to complete a 3 1/2-in pilot hole at an average rate of 7.8 ft/min. On the second run, Scale Blaster cleanout run completely cleared the 4 1/2-in tubing of heavy FeS deposits at a rate of 2.6 ft/min.
