Maximizing Value from Well Abandonment through Shallow Gas Hunting and Integrated Well Surveillance

Abstract

Shutting the aging well for good towards the end of field life requires a lot of operational and technical considerations as well as high cost to ensure project viability and safe operation. Procedures to evaluate competent cap rock layers as natural formation barriers, well plug and abandonment (P&A) design, assurance on well barrier integrity through cement bond logging and best practices in well abandonment will be highlighted through three case studies in this paper. Data integration starting from the early exploration or development drilling phase, during production and towards the abandonment phase play key roles in the project and will be the ultimate pinnacles in determining cap rock intervals, cement integrity, tubulars condition, potential reservoir communication and plug setting depth in the well. Adding an extensive behind casing acoustic noise, pulsed neutron and cement bond logging campaign and full integrated formation evaluation in the picture will further enhance the feasibility of abandonment project with additional discovery of shallow gas potential to prolong the field economics. Detail analysis of petrophysical logs, mud log gas reading, well pressure monitoring, shallow gas hazard site survey and acoustic-noise log deliverables have revealed the presence of shallow gas as deep as 300-400 m below the sea bed and few more intervals at deeper or shallower depth. Incorporating all available data to date had resulted in extensive volume of gas-in-place being evaluated, thus driving additional value through potential workover or shallow gas appraisal project prior to abandonment. In addition, operational cost, time and safety will be further optimized through cap rock restoration method and cement recipe upgrading. In a nutshell, packaging shallow gas potential and possible work-over or appraisal campaign for quick field monetization prior to abandonment will prove to justify the project economics. Changing the game from conventional gas producer to shallow hanging fruits opportunity is worth to be exploited in this case.