| Abstract |
The history of geothermal investigations in high temperature areas spans over 50 years and involves projects in Iceland and abroad. Initially surface exploration is carried out by mapping the research area employing several methods based on geology, geochemistry and geophysics. The results are generally presented as a preliminary conceptual model of the area. The next phase in the research program is to drill exploration wells. Carrying out the exploration program requires geothermal knowledge both of the drilling crew and the research team. The design program for the wells has been rather consistent through the years as well as the research program, but even so progressively developed. The standard procedure for drill site investigations has for the last decades comprised a team of geologists and geophysicists as geothermal consultants. The main task of the geologist is to analyse the drill cuttings to provide information about the geological formation drilled into, prepare lithological logs and map the distribution of the alteration minerals. Furthermore, the geologist also gathers all data concerning the drilling procedure, including measurements of the circulation fluid, technical parameters such as weight on the bit, penetration rate, rotation of the bit and the torque. The geophysicist and the logging engineer run all necessary downhole logs, mostly temperature logs during drilling. A standard program is performed prior to casing consisting of temperature-, resistivity-, neutron-neutron-, natural gamma- and calliper logs is carried out. After cementing a casing a CBL (cement bond log) is a standard procedure to confirm a job successfully done. The completion program at the end of drilling includes the aforementioned logging program as well as an injection test and stimulation if required. The geologist and the geophysics evaluate all the data concerning the drilling project as a team in collaboration with the drilling engineer and a company representative. The intensive geothermal drilling in the last three decades in Iceland has led to significant innovation in drilling technology, exploration strategy and geothermal research. |