Innovative Perf-and-Plug System Saves More Than $800,000 by Recovering OBM and Setting Environmental Plugs in 1 Trip

Objectives

Set an environmental plug without cutting and pulling or section milling casing to remediate annuli with trapped oil-based mud (OBM) in each of two wells.

Our Approach

The operator met with Weatherford to discuss two subsea abandonment operations in the southern North Sea. Each well had OBM trapped in the 9 5/8- × 13 3/8-in. annulus at the time of well construction. The proposed remediation plan for each well entailed cutting and pulling or section milling the 9 5/8- and 13 3/8-in. casing, circulating out the OBM, setting a bridge plug, and placing a cement plug in the main bore. Moreover, the cut-and-pull operations required a jackup rig equipped with a 13 5/8-in. blowout preventer (BOP) stack, and the BOP needed replacing with a larger 18 3/4-in. size, which increased risks associated with handling unfamiliar rig equipment.
Weatherford suggested an innovative perf-and-plug system as an alternative method for significant cost savings. The system would enable recovering the OBM, remediating the annulus, and setting a mainbore plug in one trip. It should be noted that evidence of the 13 3/8- × 20-in. annular condition was provided and accepted. Weatherford could have remediated the 9 5/8- × 13 5/8-in. annulus and the 13 3/8- × 20-in. annulus with the same methodology described below, if it had been required.
After careful planning, Weatherford presented the finalized plug-and-perf procedure, which the operator subsequently accepted.
The Weatherford team deployed the system and performed the following tasks:
- Perforated 24 ft (7.3 m) below the wellhead in the 9 5/8-in. casing and opened return circulation from the annulus requiring remediation.
- Perforated below the subsea wellhead at a 1,520-ft (463.3-m) measured depth (MD).
- Set the packer and straddled the lowermost perforation at 1,500 ft (457.2 m).
- Circulated out the OBM with a surfactant spacer to water-wet the annulus in preparation for the cementing operation.
- Pump cement into the annulus to form a 530-ft (161.5-m) column chased by a cement latch dart.
- Disconnected from the straddle, which closed the ball valve on release.
- Place a balanced cement plug on top of the straddle assembly in the main bore.
In each well, the operations removed OBM from the annulus and set an environmental plug in a single trip, which left the well ready for the recovery of the high-pressure riser system and removal of the subsea wellhead without the risk of releasing unwanted fluids into the subsea environment.

Value to Customer

The unique Weatherford perf-and-plug system delivered an alternative solution that saved 2 days per well, or 4 days total, which equates to more than US $800,000 in rig time. The system also saved additional third-party costs for swarf handling and disposal by eliminating the need for section milling and cut-and-pull operations.

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Intervention and Abandonment

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Details

Location

United Kingdom, North Sea

Well Type

Offshore, oil producer

Hole Angle

36°

Casing Size and Type

9 5/8-in., 53.5-lb/ft L80
13 3/8-in., 72-lb/ft L80

Liner Size

7 in., 29 lb/ft

Depth

9,405 ft (2,867 m) TD

Top of Liner

5,600 ft (1,707 m) MD

Products/Services

Wellbore cleaning services

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Innovative Perf-and-Plug System

Objectives

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