Modelling of Completion Tests in Two Wells of the Wairakei – Tauhara Geothermal System, New Zealand

Abstract

A completion test in a geothermal well, usually conducted soon after drilling is completed, consists of pumping water at various rates into the well and carrying out pressure, temperature and spinner (PTS) runs. Then after injection is stopped pressure and temperature runs are carried out while the well warms up. The spinner test helps to identify the permeable zones (feed-zones) in the well especially the reservoir characteristics. The warming-up temperature profiles also help to identify feed-zones. The analysis of the completion tests at present is mainly qualitative and the aim of the present study is to make it more quantitative by using the geothermal reservoir simulator TOUGH2 to simulate completion tests. In this study, modelling is conducted for two completion tests carried out in the Wairakei – Tauhara geothermal field, New Zealand. The tests were for WK242 (Wairakei) and THM15 (Tauhara). The simulations were carried out using AUTOUGH2, the University of Auckland’s version of TOUGH2. For both wells, manual calibration was used to improve the match of the model results to the measured data and additionally, for THM15 some inverse modelling was undertaken with iTOUGH2. For both wells, a reasonable match to the data was obtained. It was found that WK242 has two inflows (around depth 450 m and 750 m) and one loss zone (below 950 m). However, THM15 has only one inflow (around depth 135 m) and a minor loss (around 112 m). The inflows and losses indicate the location of potential feed-zones.