Innovative Technique for Abandoning Geothermal Wells at The Geysers, Northern California

Abstract

Abandoning wells, whether oil and gas or geothermal, requires placing cement plugs across i) the productive zones, ii) at the shoe of the production casing, iii) across the fresh water interface and iv) at the surface. This is usually performed using a workover rig with tubing and is an equipment intensive, time consuming and hence, costly process. For this paper a method will be described which has been devised to reduce the time and cost by utilizing coiled tubing. Due to the high temperatures that are encountered in geothermal wells, a special bridge plug was used with a modified setting procedure that proved very successful. This method worked well in abandoning five of six wells in The Geysers Area of Northern California. The procedure could be used in other geothermal areas or in oil and gas wells. The maximum depth to which the tubing was used in these jobs was 5,000 feet; however, stronger tubing is now available that may allow use of this method to greater depths.