Coiled Tubing Live Well Cleanout

Abstract

Contact Energy Limited (CEL), with their partners Western Energy Services (WES) in New Zealand, have been pioneering live well cleanouts on production wells and reinjection wells. The most obvious advantage of live well cleanouts is very minimal production (or reinjection) downtime, and other advantages in production wells include avoiding thermal cycling of the casing and removing the wellbore scale fragments to the surface, which prevents blocking the reservoir. In 2018 CEL successfully cleaned out one reinjection and six production wells and gained back 34.3MWe of generation at only a fraction of the cost of a traditional rig workover. Since its inception, CEL and WES have cleaned out a total of 30 wells (3 reinjection wells and 27 productions) at several geothermal fields. CEL and WES are continuously developing the method and pushing the boundaries on what can be achieved.
Initial concepts for using coiled tubing in geothermal wells were developed from oil and gas technology which was then adapted to suit the harsh geothermal environment. In this environment, the highly destructive high-temperature geothermal fluid proved to be the biggest hurdle for job design and tool suitability. Our team first selected a variable vane style mud motor to power a milling bit to mechanically remove the scale from the wellbore. Although successful in multiple wells with apparent soft scale, the limited motor life resulted in poor performance for harder scale and extended milling section operations. Despite an initial success rate of less than fifty per cent over the first five attempts, both CEL and WES retained a clear appetite for innovation, fueling a path to broader thinking and design alterations that have led to recent successes. Trials on multiple candidate wells have demonstrated the suitability of coiled tubing for this purpose. Through pushing traditional boundaries, this technology continues to evolve as a trusted and reliable method to remove scale in geothermal wells. The technology has been utilised to clean out production and reinjection wells to a diameter of 14.5” ID (16” casing) and depths of up to 3000m.