First High pressure cavern Well abandonment in the Netherlands

Abandonment of a high pressure salt production cavern (>2500m TVD).

Summary data:
• Pietersbierum, The Netherlands
• Start date: May 2017
• End date: November 2017
• Goal: Plug and abandon the well and salt production cavern
• Result: Successful P&A

Project description:
After an extensive period of monitoring the well was scheduled for abandonment in 2017. Over time the cavern pressure has stabilized to (near) lithostatic pressures (up to 265 bar wellhead pressure). This high pressure resulted in some challenges regarding the well operations; as the inner completion provided an ID restriction to mechanical bridge plugs and snubbing out of the inner completion was not possible due to tubing corrosion.
To overcome these challenges, the operations were separated in different phases:
– Wireline preparations (casing & cement logging)
– Placement of a temporary cement barrier to install HWU with coiled tubing
– Final abandonment with Hydraulic workover unit (HWU).

In preparation of the operations a wireline investigation was performed to assess the general well condition. The cement log indicated a good success chance for a remedial annular cementation as part of the abandonment.
In order to install the HWU on the well was made pressure less with a cement plug, placed in the well with coiled tubing. The cement plug was placed on top of an inflatable bridge plug run through 7” casing and installed into a 10 ¾” casing.
During the final abandonment the Hydrawell HydraHemera toolstring was utilized to establish the primary abandonment plug above the cavern. This was performed as an alternative to section milling, which would be a challenging and time consuming operation, especially with the HWU.
For the secondary abandonment a remedial annular cementation (between 10 ¾” and 13 3/8” casing) was successfully performed, which was confirmed by logging. Subsequently a 100m internal cement plug (inside 10 ¾”) was set on top of a CST (cement support tool).
For final abandonment an environmental (cement) plug was placed below surface and the wellhead and cellar removed.
For this project, Well Engineering Partners provided project planning, tendering engineering, coordination, management and supervision for the project while other companies provided materials and services.