Geochemical behavior of EGS reservoir during first circulation test at Habanero Site, Cooper Basin, Australia

Abstract

The first circulation test of an Enhanced Geothermal System (EGS) in Australia was conducted from December 2008 to February 2009 at Cooper Basin, South Australia by Geodynamics Limited. The circulation test involved circulating fluid (~14 kg s-1) between an injection well, Habanero #1, and a production well, Habanero #3, for about 66.5 days through a closed-loop system in order to characterize the connection between the wells. During the circulation test, the production fluids for tracer test and geochemical analysis were collected at a sampling panel after a cooling tower near the re-injection well Habanero #1. The tracer ‘breakthrough’ occurred after 4 days and the volume at peak was about 9,000 m3. The tracer-swept pore volume was calculated to be 18,500 m3 and the fraction of tracer returned was 0.78. From the results of fluid geochemistry during the circulation test, the average concentration of Na, K and Cl was 5,107 mg/l, 694 mg/l, and 8,885 mg/l, respectively. These values were slightly higher than those of the production well Habanero #3 of the previous open-flow production test. This is considered to be due to the dissolution of feldspars in the granite at reservoir depth.