MILLING THROUGH PLUG BULLNOSE ON E-LINE, RLWI

RLWI_Milling through plug

Background

A highly deviated subsea production well in the North Sea was experiencing problems with a deep-set bridge plug. The well was drilled and completed in 1999 and producing from two different zones. During e-line intervention in 2003, the lower zone was plugged off because of high GOR and water cut. Years of pressure support in the lower zone from a gas injector had increased reservoir pressure and now the operator wanted to regain communication with the lower formation and increase oil production. The zone was shut off by a retrievable bridge plug set in a 7” liner in a 230° F (110° C) environment. It was believed that the rubber elements would not retract to its original size, thus would, be difficult to pull through the completion jewelry.

OPERATION

The original plan was to pull the bridge plug free and then releasing it in a 9-5/8” OD section. This would allow production around the released plug. But a caliper run showed a restriction in the liner 985 ft (300 m) above the plug, preventing the use of a pulling tool or the standard equalizing prong recommended by the plug supplier. Having confirmed that the bridge plug could not be pulled, the team adjusted the strategy and decided to equalize and produce through the plug. Welltec® designed a custom prong, which could pass the restriction and enable production through the plug equalizing ports. Despite applying 33,000 lbs downward force to the sleeve, it would not stay open. The team then decided to mill through the plug to create contact with the lower zone. Welltec delivered a tailored solution consisting of a 1” OD, 4.3 ft (1.3 m) long drill bit fitted on the Well Miller®. The toolstring was designed to penetrate the entire bridge plug and to mill through the plug’s bullnose. The operation was performed from a Riserless Light Well Intervention (RLWI) vessel.

ACHIEVEMENTS

This operation was a world’s first and successfully reestablished communication with the lower zone. After the intervention, oil production increased significantly (200 Sm3/d), while gas and water rates decreased. This case is a testament to the benefits of strong cooperation between operator and service provider in developing tools and methods to achieve better oil recovery and successful interventions by pushing the limits of what can be done on e-line. The ability of Welltec to think creatively, adapt and react quickly in facing this unexpected situation offshore saved valuable time as the operator avoided having to mobilize rig and CT equipment or drill pipe to mill through the restriction.

MAX. TEMPERATURE: 230º F (120° C)
WELL HEAD PRESSURE: 3,190 PSI (220 BAR)
H2S: 3 PPM

 

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This case is a testament to the benefits of strong cooperation between operator and service provider in developing tools and methods to achieve better oil recovery and successful interventions by pushing the limits of what can be done on e-line.