| Abstract |
Geodynamics Limited has been developing an Enhanced Geothermal System (EGS) in hot granite beneath the Cooper Basin in central Australia since 2002. Four wells have been drilled at the Habanero site to depths exceeding 4,200 m and all four wells have penetrated a major sub-horizontal fault which forms the reservoir within the granite. The temperature in the reservoir has been measured at 244°C at ~4,220 m below surface. From April to October, 2013, Habanero 4 and Habanero 1 were operated in closed-loop mode, with Habanero 4 as the producer and Habanero 1 as the injector. Circulation was established and maintained with the aid of a surface pump, re-injecting the produced geothermal brine back into the reservoir. The heat produced was used to power a 1 MWe pilot power station. During the trial, the performance of the closed-loop steadily improved. Production temperatures increased to 215°C and flow rates reaching 19 kg/s at the end of the trial. During the trial, two step-rate tests of the closed-loop system were conducted. These step-rate tests involved operating the closed-loop at several different pump speeds to assess the system performance and the potential for thermosiphon flow. In an effort to reduce temperature losses in the wellbore, Nitrogen was injected into the tubing-casing annulus part way through the trial period. At the end of the trial, production logs were run in both wells to provide temperature and pressure profiles for each well. These production logs were used to calibrate analytical models of both wellbores and to assess the effect of the Nitrogen. The performance of this closed-loop will be discussed and compared to an earlier closed-loop trial conducted at Habanero in 2009. By combining surface data, production logs and wellbore models, pressures, temperatures and fluid densities around the closed-loop will be discussed. |