Novel Acid Design and Technique for Removing Scale in Geothermal Injection Wells, Tiwi Geothermal Field, Philippines

Abstract

Silica scale deposition is common in geothermal injection wells die to the chemical characteistics of the brine injected into these wells. Over time, scale can accumulate in the liner, within the liner perforation, in the liner/formation annulus and in the formation close to the wellbore. If sufficient scaling occurs, the wellbore and/or permeable zones may become totally blocked and injection will no longer be possible.

Three injection wells were recently worked over in the Tiwi Geothermal Field using a combination of scale drillout (SDO) and acidizing to restore their injection capacities, with im0provements made to the acid design and the method of delivering the acid to the well when compared to previous practice. The new acid design improved both the safety of handling the chemical and the effectiveness in dissolving scale while a high pressure rotating jet nozzle (Roto-JetTM0 was used to deliver the acid rather than open ended drillpipe. This helped diver the acid through the liner perforations and into the zones of interest. Results indicated that the improvements were effective, with target injection capacities exceeded. Future workovers for scale removal are therefore likely to be conducted in a similar manner.