This paper describes the workflow, concepts, and techniques that operators should consider during abandonment planning to help ensure effective isolation for fields in which thermal recovery is executed.
In the Chichimene field of the Llanos basin of Colombia, several wells were drilled that now require permanent abandonment. However, previous abandonment projects performed in other fields were challenging because several interventions were required to ensure isolation, which increased operational expenses. Additionally, the operator implemented new techniques to improve oil recovery in the Chichimene field, which presents additional challenges for isolating intervals of abandoned wells because of thermal cycles with high temperatures that can exceed 500°F. Sour gasses are also encountered in this field.
These challenges require nontraditional techniques for successful isolation of the intervals as well as an enhanced methodology for decision making, such as an assessment of the current downhole conditions using ultrasonic logs to evaluate casing corrosion and cement sheath integrity. This allows evaluation of the well before and after abandonment and includes measurement of the sour and explosive gases at surface to validate the barrier, design of fit-for-purpose cement slurries to withstand downhole conditions, and use of displacement fluids to help minimize casing damage. This holistic cost-effective abandonment method has been performed in seven wells in the area with excellent results, indicating that the approach can be a beneficial option for other fields with similar conditions and requirements. Additionally, oil and gas operators can use this methodology as an alternative to help improve results for well abandonment. Zero nonproductive time (NPT) or health, safety, and environmental (HSE) incidents were recorded during these projects.
This paper also discusses the importance of safety and environmental risks associated with abandoning an asset, which can be mitigated through engineering for optimal zonal isolation in unconventional fields.