Modeling Validation of Tubing Compaction for Rigless Well Plug and Abandonment

Abstract

Summary Conventional well plug and abandonment (P&A) can sever and remove the tubing to access casing or leave it in situ when it does not interfere with providing a seal over an indefinite time frame. This paper assesses the viability of pushing rather than pulling severed production tubing to gain casing access. The P&A decision to push, pull, or leave the tubing in situ depends on confirming existing seals and then placing suitable sealants, such as cement, to keep the risks of future well leakages as low as reasonably practicable (ALARP). Pushing or compacting tubing into the liquid space of a well could be used with smaller rigless units, which cannot hoist the production tubing, but can use production intervention or decommissioning logistics with coiled tubing or wireline cutting and severance. Associated pumps could then drive an inflatable piston to compact split and severed tubing into a lower liquid space to access casing for logging and P&A plugging. Rigless tools and methods have provided dramatic cost savings where casing access was not needed, and thus the present study investigates the viability of accessing casing by means of pushing or compacting tubing to extend rigless P&A use and savings. The viability of pushing and compacting North Sea sizes and grades were confirmed in real-scale physical-compaction simulations of production-tubing joints pulled from offshore wells. Independent small-scale physical simulations and numerical modeling then confirmed that the real-scale results were predictable and repeatable to demonstrate an ability to design and provide a window or gap in a production-tubing string for use by other P&A methods.