Broaching, an Effective Method of Wireline Intervention for Calcite Scale Removal

Abstract

Calcite scaling is the leading cause of production loss in Geothermal wells. The most common well intervention technique to combat the issue of scaling is a drilling rig workover. The average cost of well workovers has increased considerably in the last 5-10 years, resulting in an economical conflict to workover certain wells. In 2013 Contact Energy (Operator) and Western Energy (Service Company) researched, developed, trialled and implemented a wireline intervention technique and methodology to successfully remove and reduce calcite scale in the Ohaaki and Wairakei geothermal fields in New Zealand. This wireline intervention technique, called broaching, is a process developed in the oil and gas industry which uses mechanical tools to remove mainly silica from small diameter production tubing. This process has been transformed to accommodate the geothermal industry by designing tools to combat large volumes of calcite in larger diameter casings. Contact and Western Energy have successfully utilised Broaching to workover 13 geothermal wells and regained over 22MW of production for less than 50% of a traditional single well workover. Perhaps the largest benefit of broaching is that the wells targeted for broaching would have been uneconomic or unfeasible to work over using a rig, broaching has allowed wells that have been dormant for years to contribute to electricity generation. Contact and Western Energy are continuously analysing empirical data from previous broaching jobs to improve tool development, operations and broaden the available window where broaching can be an effective method of geothermal well maintenance. Tool technology, well conditions, wireline experience, and calcite conditions are some of the many outlying variables determining broaching success.