| Title | Post drilling outer casing cement remediation and recommissioning of a Rotokawa well |
|---|---|
| Authors | M. Kelley, D. Chaparro, O. Goh, B. Murphy |
| Year | 2024 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Rotokawa, well engineering, cement squeeze, well workover, well warm-up model, commissioning |
| Abstract | This paper describes the successful remediation of a geothermal production well in Rotokawa, New Zealand six years after its drilling which left it with an incomplete cement job on an outer casing annulus. As an initial risk mitigation prior to commissioning in 2017, a pack-off assembly was added to the effected annulus to contain any shallow hot aquifer fluids, to allow thermal expansion of trapped water between the casings, and to allow the well to be put into service. While this was effective initially, the cement job in this annulus continued to degrade over time, allowing the release of shallow fluids through the annulus and pack-off. The leak rate became unmanageable, and the well was shut in November 2022 until a proper repair could be implemented. The repair plan included upgrading the annulus pack-off hardware and conducting a reverse cementing method to recement in the casing. To reduce the potential of failure of the 24” casing connections and risk of casing collapse, a detailed re-commissioning warmup program was designed to slowly release potentially trapped water in cement voids between the casings. This program included a prescriptive flow schedule developed using a volumetric and heat transfer-based digital model of the wellbore fluid movement which was calibrated and confirmed by implementing downhole wireline and surface monitoring techniques. The well has since been returned to service, with monitoring showing that the repair job was competent. The reverse cementing and warmup modelling methods should be useful on future similar types of well interventions. |