Section milling during plug and abandonment of petroleum wells

Abstract

During plug and abandonment (P&A) operations of petroleum wells there is often a need to remove casing in order to set competent barrier sealing in all directions. If the casing cannot be cut and pulled, a section milling operation has traditionally been the solution. The P&A is an expensive operation that offers no value creation, and the economic situation of the industry along with stricter regulations is causing an active search to strongly reduce rig-time and costs.

To address the situation, this thesis is compiled with an investigation into the P&A industry with a particular focus on the section milling operation and its requirements. The challenges of section milling have been discussed in depth with relations to performance enhancement, and statistics has been presented and compared with novel methods with the aim to define improvement potential. Investigated alternatives include perforate, wash and cement (PWC), upward section milling, melting, chemical degradation and the crushing of tubular.

The results show that the main disadvantage of the section milling is the swarf generation and handling of it with addition to HSE issues, violent vibrations and plug verification. The improvement of the cutters and the milling fluid has been presented as the most important factors for performance enhancement. The investigation into novel methods show that several technologies have the potential to substitute section milling and to significantly reduce duration and cost, with the largest documented potential being PWC’s ability to cut the expected 24-day multiple casing section mill operation by 83%. However, further development is needed in order to refine the technology before it can replace section milling completely.