THRU-TUBING PLUG-BACK PROJECTS
Low Cost/High Success Rate Thru-Tubing Intervention Projects
Thru-tubing plug-back projects are a low cost/high success rate alternative to expensive rig jobs.
Thru-tubing plug-back projects use a thru-tubing bridge plug (T-TBP) and special cement slurry system to achieve zonal isolation in casing. T-TBPs allow operators to run thru small restrictions and set in casing diameters four times the T-TBP run-in diameter. T-TBPs are typically run on WL, slickline, and CT.
· Project Goals – The three most common thru-tubing plug-back project goals are:
i. isolation of a well zone, therein providing the option of perforating a well zone, up-hole,
ii. interzonal isolation between existing perforated intervals, and
iii. temporary or permanent abandonment of a well or specific well zone.
· Projects Per Year – Worldwide, over 4,000 thru-tubing plug-back projects are performed each year. Nearly 90% of these operations are conducted on WL. The remainder are done on slick-line, CT, and some on threaded pipe.
· Success Rate – The estimated success rate for plug-back projects where vented T-TBPs are run on WL and slickline is greater than 95%. When positive sealing T-TBPs are run on WL it is greater than 90%. The estimated success rate for CT run positive sealing T-TBPs is 70 – 90% depending on the type of T-TBP run and the expansion ratio.
· Classification – Thru-tubing plug-back operations are typically categorized as thru-tubing intervention operations, more specifically, thru-tubing remedial wellhead operations.
· Equipment – Generally, thru-tubing plug-back operations are done with a T-TBP, a dump bailer cement slurry system and conventional WL, slickline, and CT equipment. Special cement slurry systems are used in thru-tubing plug-back operations. Conventional WL, slickline and CT equipment is used to run and set T-TBPs. The T-TBP, alone, is rarely considered a long-term pressure isolation mechanism. The T-TBP serves as a platform for cement slurry that is placed atop the T-TBP. The cement slurry sets up in the static space above the T-TBP, affects a hydraulic seal and affects an anchoring bond with the ID surface of the casing. The cement plug provides a long-term pressure isolating seal that is anchored in place for the lifetime of the well.
· Plug-back Operations – T-TBPs are deployed via conventional WL, slickline, and CT operations. T-TBPs are run thru the wellhead, thru small restrictions and set in casing. Cement is placed atop the T-TBP to obtain a long term high differential pressure plug. In WL and slickline operations gravity and positive displacement bailer systems are used to place cement atop the T-TBP. Cement used in CT operations is also special. Unique controlled volume placement techniques are used when placing cement via CT.
· Benefits – Often, the cost of a thru-tubing plug-back project is a small fraction of the cost of a “rig job” on the same well. This is especially true for offshore wells. The combination of low cost and high success rates make thru-tubing plug-back operations an economically attractive method to plug-back wells.
Glossary of Terms
§ Dump Bailing Placement of Cement – The bailer system is a series of tubular joints that are threaded together, filled with special cement slurry and conveyed in the hole via WL, slickline or CT. The bailer system is positioned immediately above the T-TBP. The trapping mechanism at the bottom of the bailer system is selectively opened and the load of slurry is placed atop the T-TBP.
i. Gravity Bailer Systems – Gravity bailer systems conform to the general bailer system description, above. When the trapping mechanism is opened gravity causes the 17 ppg slurry to exit the bottom of the bailer and settle atop the T-TBP.
ii Positive Displacement Bailer Systems – Positive displacement (PD) bailer
systems conform to the general bailer system description, above. However, when the trapping mechanism opens the slurry is expelled via a biased positive
displacement piston. PD bailer systems assure slurry placement and eliminate the chance of cement getting “strung up the hole.”
§ Thru-Tubing Bridge Plugs – A specialty plug capable of running thru small restrictions and setting in casing diameters three times its’ run-in diameter. Alone, a T-TBP is rarely considered a long term or permanent isolation mechanism. Typically, T-TBPs serves as a platform for cement slurry that is placed atop the T-TBP. The cement plug provides a permanent anchor and a long-term hydraulic seal.
i. Positive Sealing T-TBPs – These plugs conform to the general T-TBP description, above. What makes this plug unique is that immediately upon setting, this plug system provides a positive compression seal which holds differential pressure. This immediate seal provides numerous economic and operational benefits not offered by vented plug systems.
ii. Vented T-TBPs – These plugs conform to the general T-TBP description, above. Vented T-TBPs do not affect a positive casing seal. Their principal function is to provide a platform for the cement slurry. A vent tube provides a path to accommodate flow of wellbore fluid related to wire-lining in and out of the well during plug-back operations. Vented T-TBPs provide a static annular casing interval where the cement slurry can set up, bond to the casing, form a seal with the casing, and anchor the seal in place.
Dump Bailer Cement Systems – These special slurry systems are engineered to assure “dumpability” after long descents in severe well conditions. Dump bailer cement slurries are also engineered to provide maximum hydraulic seal with excellent anchoring. Admixes provide these slurries with low friction properties, excellent suspension characteristics (assuring homogeneous density upon gelling), and rapid gelation at 3-4 hours after placement, therein, abating channeling. Dump bailer cement systems are very special; multiple dump bailer batches accumulate to produce firmly anchored cement plugs with long term hydraulic seals.
NeoProducts®is a world leader in thru-tubing plug-back technologies and services. NeoProducts provides the global oil industry with service specialists (if desired) and thru-tubing plug-back equipment. NeoProducts offers vented T-TBPs, special plug-back slurry systems and services. WL and CT companies throughout the world run NeoProducts equipment. Contact NeoProducts for more information on your thru-tubing plug-back projects.