SL was used to swage open the CT fish inside the overshot with a 1.5-in. swage. The SL unit was rigged down. The next step was to cut the CT as deeply as possible. Electric line (EL) was rigged up and a 1.375-in. gauge ring was run to 14,000 ft. The 2-in. CT had 5,600 psi and the annulus had 11,800 psi. A total of 250 bbl of 11.8lbm/gal calcium bromide was circulated. The 2-in. CT had 5,400 psi and the annulus had 6,050 psi. The operator RIH and jet cut at 14,000 ft. The EL was then POOH and rigged down. Pipe was moved with 21K pipe weight to confirm the cut. EL was rigged up and 42 bbl was bullheaded down the CT. The operator RIH and set the first bridge plug at 11,800 ft. A 5K negative test was performed on the plug for 30 minutes. The operator then RIH with the second bridge plug and set it 30 ft higher at 11,770 ft. As soon as the second plug was set, both plugs leaked. The operator RIH with the third bridge plug and set it at 11,200 ft. Following, 4.5K negative plug leaking was performed. The operator RIH with the fourth bridge plug and set it at 10,200 ft. A 4.5K negative test was performed. The operator RIH and the fifth bridge plug was set at 10,100 ft. EL was rigged down and the CT was bleed to 0 psi. The overshot was removed and the HWO unit was rigged down. All plugs leaked 5,600 psi on the CT. The decision was made to disregard placing plugs in the CT with the weld flash because five consecutive plugs had leaked. As Fig. 2 illustrates, the weld flash can present a difficult challenge for standard elastomers. It can be very difficult for an elastomer to mold itself into a 90° right angle configuration with a standoff of 0.120 in. and still maintain a seal in excess of 5,000 psi. The surface pressure had been as high as 11,800 psi. The next step was to rig up the HWO unit and proceed with the slip/shear fishing method. An overshot was run in the hole and the CT fish was latched and pulled more than 50 ft. The fish was secured with slip rams and sheared. The sheared 50-ft section was laid down. The slip/shear method was continued for five additional cuts before the CT fish fell out of the overshot.
on the composite plug including the heavy metals is beyond the scope of this paper; rather, the focus is on lessons learned from the time the pipe became stuck until the fish was retrieved. Listed below are options for the operator if the CT becomes stuck and the BPVs are not sealing: ● Kill the well with kill weight fluids. ● Spot a swellable solution. ● Spot cement. ● Freeze and cut CT. ● Shear/cut CT and endless possible solutions. Shear rams are good for cutting pipe and stopping uncontrolled flow. However, shear rams have caused several underground blowouts when they are closed on tubing with a higher surface pressure than the annulus. Uncontrolled flow allows the workover fluids to be replaced with formation fluids and gas, which can reduce hydrostatic pressure. Once the shear rams are closed, the higher pressure is exposed to the top of the annulus fluids because BOPs are not designed for pressure from the top. It is possible that the well could have been circulated or bullheaded and the pressure could have been stabilized under 6,000 psi. Some plugs do a fair job of sealing the weld flash at low pressures; however using a bridge plug to seal in the weld flash at high pressures greater than 10,000 psi with a 0.120-in. weld flash (as in the project discussed) is not recommended. Therefore, the question remains regarding what type of plug has a good record of sealing on weld flash at high pressures. Freezing, swellable, and cementing methods are good options that can mold themselves to the irregular IDs presented by the weld flash. Bridge plugs and inflatables packers perform fair in lower pressure environments. Fig. 3 illustrates a decision tree with several options for tested barriers available without shearing the CT. Shearing is always an option and more often with weld flash present.
Conclusions
At this point, it was determined that the fishing needed to occur in the wellbore, rather than the BOP stack. The CT fish was latched, pulled back into the BOP stack, and the slip/ shear method continued. A total of 276 cuts were made with an average length of more than 50 ft each. Once the fish was removed, the HWO unit was rigged down. Table 1 illustrates that it is possible to retrieve more than 900 ft in a 12-hour day with 6,000 psi at surface.
If the weld flash is removed, most plugs on the market have a good chance of sealing within their working pressure range unless extreme ovality is present. The real problem is that weld flash cannot be removed from a CT tapered string, which accounts for more than 90% of the CT manufactured in 2013. The advantage of the tapered string is that it increases operating depths, which is quite desirable. The inside cutter is currently fixed in place and will not move to accept a change in tubing ID or wall thickness.
Issues
Currently, no bridge plug manufacturers promote plugs that seal on a weld flash without applying cement on top. This
The topic of preforming annular velocity (AV) calculations
Petroleum Today - June
2017
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