Fishing Coiled Tubing With Internal Weld Seams and Failed BPVs in a Live

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. 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.

Issues

The topic of preforming annular velocity (AV) calculations 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

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. Currently, no bridge plug manufacturers promote plugs that seal on a weld flash without applying cement on top. This

is because the weld flash prevents one of the slip segments from engaging the CT and also makes sealing almost impossible because the weld flash protrudes at a 90° angle from the inside wall up to 0.120 in. Fig. 4 illustrates 2-in. CT with the weld flash removed on the left and 2-in. CT with the weld flash installed on the right. It’s almost a no-brainer to understand the difficulties relating to setting a bridge plug and maintaining a seal in a high pressure environment with the weld flash in place (Fig. 4, right). It is fairly easy to have the weld flash removed during the manufacturing process if the string has the same wall at a cost of less than USD 1 dollar/ft.

Recommendations

In today’s well environment, a good philosophy is that, if you cannot seal it, do not put it in the well. This is true for almost everything except CT with a weld flash. Tapered CT is desirable in some instances, but also comes with risks. Failure to seal can lead to one of the following scenarios: ● Kill fluid as the only barrier. ● Killing a USD multimillion fracture job. ● Pumping cement and hoping for the best. ● Pumping something swellable. ● Pumping something that sets up. ● Freezing the CT. ● HWO unit—employing a slip and shear fishing method, which produces almost 1,000 ft per day of CT fish at almost any wellhead pressure with 21 different BOPs and valves. ● Shearing and worrying about it later. The author recommends only running flash free CT. However, the weld flash cannot currently be removed from tapered CT, which is more than 90% of the market. Therefore, operators must be prepared for one of the above discussed scenarios. Fig. 5 illustrates just the BOP stack required to fish CT under pressure using the slip/shear method.

Figure 1—A 340K HWO unit was rigged up and tested. Figure 2—Weld flash.

Figure 3—Decision tree.

Figure 4—(Left) 2-in. CT with the weld flash removed; (right) 2-in. CT with the weld flash installed.

Figure 5—Just the BOP stack required to fish CT under pressure using the slip/shear method.

Table 1—12-hour day.

HVDC Enables Subsea Active Production Technology

By

Richard Voight, INTECSEA

Abstract

A growing number of projects are employing some form of subsea processing. Integrated system approaches to subsea processing, commonly known as Subsea Active Processing Technologies (SAPT), can require a great deal of power. Subsea boosting and/or separation pumps can easily reach 3 MW each; with multiple pump installations quickly adding up to a substantial demand on a host facility. When the power transmission distances approach 100 km or more, AC power distribution becomes less and less practical. For this reason, power industry leaders envision the future installation of offshore electrical utility infrastructures based on High Voltage DC (HVDC) Transmission Technology, just as they are presently employed for land based utilities. Taking advantage of these large HVDC offshore power grids for small, isolated subsea installations requiring only moderate power levels calls for adapting HVDC technology to a scale sized to the power requirements of these installations. The HVDC Power Buoy concept, proposed for isolated SAPT installations requiring subsea power in the range of 10 to 20 MW, is one such adaptation. This paper will present the HVDC Power Buoy concept and its key components; the benefits and drivers for its development; the perceived qualification challenges as well as the target applications for the technology.

Introduction

To introduce the HVDC Power Buoy concept, a subsea completion, with subsea processing included, with a tieback distance of 150 km and a total subsea power requirement of 15MVA @ 0.7 PF (10.5 MW) is used as a demonstrative test case. First, the case of providing AC power to the subsea completion is considered to illustrate the issues associated with AC power transmission. Then, as an alternative, an HVDC Power Buoy with a HVDC power transmission link is presented to show the advantages of this approach. Since the HVDC Power Buoy is a new concept, the technical gaps are then identified with suggested paths forward to mitigate said gaps. By enabling the use of HVDC power transmission, the HVDC Power Buoy concept is expected to make Subsea Active Processing Technology practical for many isolated and otherwise stranded subsea fields.

Acronyms

Ó AC Alternating Current Ó C Capacitance Ó Cx Capacitive Reactance (2*Pie*Frq*C) Ó DC Direct Current Ó Frq System Frequency Ó HV High Voltage (69,001V-230,000V) Ó HVAC High Voltage Alternating Current Ó HVDC High Voltage Direct Current Ó L Inductance Ó LV Low Voltage (<600V) Ó MV Medium Voltage (601V-69000V) Ó PF Power Factor Ó Pie 3.14159….. Ó PMS Power Management System Ó R Resistance Ó SAPT Subsea Active Processing Technology Ó SCR Silicon Controlled Rectifier Ó VA Apparent Power in Volt-Amps Ó Var Reactive Power in Volt-Amps Reactive Ó VFD Variable Frequency Drive Ó Vin DC Transmission Line Input Volts Ó Vout DC Transmission Line Output Volts Ó VSC Voltage Source Converter Ó W Real Power in Watts