Expanding the Well Intervention Scope for an Effective P&A Operation

Abstract

Over 2500 wells on the Norwegian Continental Shelf (NCS) will at some point have to be permanently plugged and abandoned. As the drill rig rate contributes to 40-50% of the total plug and abandonment (P&A) cost, the potential savings in shifting operations towards a rigless approach could be significant. The main objective during a P&A operation is to restore cap rock functionality, by creating a cross-sectional barrier. The conventional way of plugging wells on NCS is to use a rig, to allow pulling tubing, section milling or perforate, wash and cement operations to be executed.

This thesis presents an alternative approach to P&A using well intervention equipment in combination with some emerging high-energy technologies intended for rigless P&A. Wireline and coiled tubing with associated equipment and tools are used together with an electric plasma miller and/or thermite to create a cross-sectional barrier in a through tubing and X-mas tree P&A operation. A case study is presented where three wells are plugged using a rigless approach. The wells have an increasing P&A complexity, where lack of annular barrier traditionally requires a rig.

The case study identified several challenges with the presented rigless approach. A through tubing operation will leave the tubing as a major restriction in the well. All tools have to pass through the tubing before reaching the required plugging interval. Azimuthal bond logging tools intended for logging production casing cement will have particular difficulty passing tubing of 5-1/2” and smaller. Additionally, placing enough thermite to comply with current NORSOK D-010 specifications was found challenging. New revisions of NORSOK D-010 should allow the implementation of new technology and rigless P&A to open up for a leaner approach to P&A. The majority of the wells studied were not fully suited for a complete rigless P&A operation, but the approach could be used to install permanent reservoir barriers. By completing parts of the plugging operation using well intervention equipment, the P&A scope for a rig could be minimized and thereby potentially saving cost.