Borehole geology, hydrothermal alteration and structure of well SV-26 in the Svartsengi area, SW-Iceland

Abstract

This report describes the stratigraphic sequence and alteration in drill hole SV- 26 in the Svartsengi high-temperature field, SW-Iceland. Well SV-26 is a make-up and exploration well for the Svartsengi power plant. It is a directional well deviated to the east towards the southern part of Mt. Sýlingarfell to explore and extend the southeastern part of the Svartsengi production field. The stratigraphy of well SV-26 is characterized by basaltic lava flows and different hyaloclastite formations. Drill cuttings in the uppermost part of the well are characterized by a high degree of oxidation. Three alteration zones were observed: Unaltered zone (0-112 m), smectite-zeolite zone (112-622 m) and chlorite-epidote zone (622-1394 m). No drill cuttings were available for analysis below 1394 m due to total loss of circulation within the well. Aquifers in this well were located based on borehole measurements and records of circulation losses. It is important to note that the temperature loggings and mineral sequences of SV-26 do not show any evidence of temperature reversal which implies that the Svartsengi geothermal system could extend further to the east than previously believed