Well History: Well was completed with 3-1/2" 12.9 # P-110 tubing. Observed Max LEL 43% & 57%, H2S 23 ppm & 38 ppm on sensor on surface during coring in interval 12,600’ – 12,630’ KB & 12,966’ – 13,006’ KB, respectively. Recorded max BHP of 9,385 psig & BHT of 307 degF at 12,500’ KB.Max CO2% mole is ~ 8.6%. Well had never flowed except it was offloaded after DFIT & N2 kick-off for only few hours.
DFIT: Attempted DFIT (Diagnostic Fracture Injectivity Test) with 10 ppg filtered brine at rate of 0.3 bpm, while production casing was pressurized at 1,500 psig. Observed no breakdown. Bled off pressure to 0 psi. Attempted DFIT with 10 ppg brine at 0.5 bpm for 2nd attempt. Reached till 13,500 psi, observed no breakdown. Reattempted DFIT at 0.5 bpm, reached till 13,500 psi, observed no breakdown. RIH (run in hole) with CT (coil tubing) while circulating 10 ppg brine. Total brine pumped ~ 212 bbls. Pumped ~ 8 bbls of 15% HCL acid at ~ 1.5 bpm across perforation interval 12,972’ – 12,980’ KB. Pumped ~ 7 bbls of 15% HCL acid at ~ 1.5 bpm across perforation interval 12,532’ – 12,558’ KB. Stationed CT at 12,984’ KB & performed bottoms up with brine. (Maximum Exposure/Contact time of HCL with tubing ~ 1 hr during bottoms up). Spotted ~ 16 bbls of 15% HCL acid with CT at 12,984’ KB for acid squeeze job. Pumped brine down the CT till CT & CT-Tubing annulus pressurized to ~ 3,200 psig. Pressurized production casing to 1,500 psig. Pumped 10 ppg brine at 0.4 bpm for DFIT. Observed breakdown at ~ 9,274 psi. Pumped 150 bbls of brine at 8,400 & 8,700 psi. Offloaded the well with N2 and kick off through CT. Stationed CT at 11,000’ KB, increased N2 rate to 550-600 scf/min. Observed brine & spent acid slugs on surface. Shut in well. Observed pressure build up trend. Observed pressure build up to 190 psig.
Well Integrity Issue: Observed SIWHP (shut in wellhead pressure) = 0 psi (BPV was installed), TBG/CSG annulus pressure = 1,660 psig. Bled off TBG/CSG annulus pressure to 100 psig. Retrieved BPV. Observed SIWHP = 3,375 psig, TBG/CSG annulus pressure = 3,370 psig. Bled off annulus pressure from 3,380 to 2,000 psig, observed drop in SIWHP from 3,500 to 2,459 psig. After multiple bled-off/build-up attempts, it was concluded tubing has developed a leak. Attempted to drift tubing with 2.36” & 2.345” GC (gauge cutter), tagged restriction at 2,834’ KB inside tubing. Found jagged metal obstruction mark on LIB (Lead impression block) at 2,834’ KB. Shallowest point of communication was at ~ 2,812' KB.
Tubing was retrieved & found parted at different depths (~ 2800' KB, 3700' KB & 4100' KB) Pics are attached. Some parted tubings has developed cracks/fractures on it. After thorough research, following factors deemed appropriate which might had caused the tubing to fail.
- Contribution of environment i.e; H2S & CO2% mole.
- Well Treatment fluids (HCL & corrosion inhibitor)
- Cooling effect immediately after acid wash
- Contribution of stress (Hoop Stress factor) during DFIT after acid wash.
I had never came across any research paper which could explain the failure mechanism of P-110 tubing considering the all above 4 factors simultaneously. Kindly share your expert opinions to steer our investigation of P-110 failure. Please mention if any factor seems suitable or had contributed.
------------------------------
Lajpat Rai
Petroleum Engineer
United Energy Pakistan Ltd
Karachi City
------------------------------