Well abandonment operations represent pure cost to the operator without return on their expenditure. However, to manage future liability, these activities are critically important. Performing them correctly involves detailed planning. Good practice places a permanent barrier across the wellbore in competent cap rock and embeds all tubulars in the cement. Herein lies the main challenge for well abandonment; annular isolation is sometimes compromised or wasn't there from the start (e.g., subsea wells). Addressing these annular isolation issues results in extra steps in the well abandonment process, translating into extra time and money for the operator.
This paper will discuss field-proven, cost-effective solutions for casing removal including reducing the surface footprint or providing a single-trip solution that lowers the overall cost of operation.
Multiple case histories will highlight different challenges, solved by novel ideas and a combination of surface systems and downhole equipment.
Case History 1: 13⅜-in. casing partially stuck in the well needs to be removed, a single cut-and-pull operation was not successful and milling was not an option due to shallow/weak formation and equivalent circulating density (ECD) issues. Advanced milling technology enabled 30 casing cuts in a single trip in short sections, allowing each section to be pulled free using the rig's pulling capacity while minimizing surface handling.
Case Study 2: Platform load capacity or pulling capacity limitations often lead to challenging casing removal operations for slot recoveries and/or permanent well abandonment. Exercising downhole pulling force by anchoring in a larger casing size and utilizing pump pressure instead of overpull enables freeing of pipe with limited surface capabilities. Multiple examples will be shown, including time saved.
Case Study 3: Platform conductor removal operations can be very challenging when the type of connectors cannot carry the full conductor load with inner casing strings. A Rigless solution performing simultaneous operations with the main platform rig, using a sacrificial casing string to pull from the bottom provided a cost-effective solution.
Case Study 4: Platform conductor removal where the conductors have been previously cut and now stand in the water column present challenges of a different kind. The limited platform size led to a casing jacking solution with guide wires that safely and cost-effectively remove the conductors from below the mudline without bringing in a jack-up rig.
A "now what" selection guide at the end of the paper provides an overview of different solutions available, depending on downhole scope of work and the surface capabilities.