Plugging and abandonment (P&A) is the largest category of decommissioning expenditures, representing 40–44% of the total investment. If the well operator performs P&A inadequately, results may include water flows, gas or oil seeps from the seabed, or underground crossflow between formations, with a huge effect on the environment and marine life. This paper presents current advances in the development of a plasma-based milling tool and its use in casing-section milling for P&A.
Only 7% of existing North Sea installations have been decommissioned, which creates an enormous opportunity for companies engaged in such a business. Naturally, operators worldwide are seeking effective solutions that would cut the massive expenses of decommissioning.
Each P&A job depends on well construction, well location, production history, casing condition, and many other factors. From time to time, there is an option to use a rigless solution for P&A. In this case, the well is plugged without pulling tubular or milling casing. Cement plugs are set directly to the production string, and, after successful pressure tests of the plugs, wellhead and casing strings are cut with a special device a few feet under the seabed and removed to surface. P&A in a wet-tree scenario is more expensive. Because all operations occur under water, remotely operated vehicles are needed. For this type of P&A, the deployment of a heavy rig is preferred, which is more expensive. Present casing-milling technology consists of using the common casing-section mill. This mill is a hydraulically actuated tool used for milling a section in casing or tubing. The main part of the mill consists of milling knives dressed with tungsten carbide. Once the casing mill is run into the hole to the desired depth, the circulation of drilling mud starts.
Plasma-Based Tool Facilitates Plugging and Abandonment
05 December 2015