Radial Drilling Application in Geothermal Energy Recovery: Job Review and Execution Procedures based on Wells Fürstenfeld 1 and 2
Research output: Thesis › Master's Thesis › Research
Worldwide energy demand was increasing tremendously during the past century, and is expected to increase even more in the future. As the energy production from conventional natural resources is reaching its limit, new technologies have to be developed and deployed in order to meet the increasing demand. At the same time, those technologies shall be environmentally friendly and contribute to the goal of a worldwide reduction in CO2-emissions. One technology, which could help to reach those goals, is geothermal energy production. In Austria, several geothermal projects have been already installed. One of them was the teleheating system in Fürstenfeld, which consisted of the two wells FF 1 and FF 2. However, it encountered several problems at various stages of the project, the main problem being the low injectivity of well FF 2. Therefore, the aim of this thesis was, to review the whole execution process of the two geothermal wells in order to identify potential failure reasons. Thereafter, potential technologies to increase the injectivity had to be identified. The beginning of the thesis reviews the execution process of the two geothermal wells FF 1 and FF 2. It starts with the regional geological setting where the wells were drilled, including the characteristics of the encountered layers. The second step was to review the drilling process. In doing so, also problems which were encountered at that stage of the project, like surface coating reliefs and a broken tubing, were discussed. After the wells were drilled, production and injection tests were performed on both wells. The thereby obtained results and parameters are consequently presented. The second part of the thesis reviews well intervention methods used on oil and gas wells to increase production and overcome near wellbore damage. Thereby, the focus was a comparison between radial drilling applications and hydraulic fracturing. In doing so, the feasibility of those two methods regarding implementation on geothermal wells was evaluated. Prerequisites, favourable deployment environments, as well as advantages and disadvantages of both intervention methods were presented. Also requirements regarding equipment and HSSE aspects were included. As geothermal wells are always very sensitive regarding costs of a well intervention, also this point was briefly discussed by comparing the magnitude of expected expenditures. The last part evaluates the influence of radial drilling on the injectivity of well FF 2. Therefore, pre-intervention injection models were set up by Prosper and calibrated considering production/injection well-test data. Afterwards, a multi-radial Prosper model was created and the potential increase in injectivity was identified. As a result, injection rates increased from 11.4 m³/hour to 133.8 m³/hour after the implementation of radials could. For the implementation of the radials, a sensitivity analysis identified vertical permeability as the main influencing factor for injection rate. Thereby, the injection rate varied by 123 % comparing low vs. high vertical permeability cases.