Achievements and Ongoing Progress of the European HiTI Project: High Temperature Instruments for Supercritical Geothermal Reservoir Characterization and Exploitation

Abstract

The HiTI project (High Temperature Instruments for supercritical geothermal reservoir characterization and exploitation) was funded within the European Sixth Framework Programme (FP6), lasting three years and starting in 2007 . HiTI brings together geothermal downhole sensor developers and research institutes. The project is providing geophysical and geochemical sensors and methods to evaluate reservoirs and deep geothermal wells up to supercritical conditions (temperature above 374 °C and pressure exceeding 22 MPa for pure water). Supercritical geothermal wells are presently non-conventional but may provide a very efficient way to produce electricity from a clean, renewable source.

The set of new instruments tolerate high temperature & pressure in a highly corrosive environment. A slickline tool (memory tool) tolerating up to 400°C and wireline tools up to 300°C are developed, the latter lower limit due to the present limitation in wireline cables (320°C). Furthermore, geothermometric methods are developed to address temperatures beyond 400 °C. The new downhole tools are demonstrated in Icelandic high-temperature geothermal fields. Temperature, pressure, fluid flow and casing collar location might be measured up to 400°C from a single multisensor tool. Natural gamma radiation spectrum, televiewer signal (acoustic), electrical resistivity and fiber optic cables using distributed temperature sensing method are also being developed for borehole applications up to 300°C.

For a better understanding of supercritical reservoirs, a HPHT (high pressure high temperature) laboratory has also been adapted to study the electrical resistivity of rocks and fluids, as well as rock rheology and chemical processes in supercritical conditions. A Na/Li geothermometer, based on chemical and isotopic analysis of Icelandic fluids, has been developed to determine reservoir temperature and rock nature. Moreover, tests with organic tracers tolerating up to 350°C are performed, to evaluate the reservoir storativity and flow rate in the Krafla geothermal field.

Identification of new concepts of tools and evaluation methods at temperatures beyond 400 °C, conducted within the project, will potentially lead to future development of very high temperature geothermal instruments and methods, increasing our knowledge of supercritical reservoir behaviour and our abilities to exploit such resources.