Planning of a Deep Geothermal Well to Reach Supercritical Steam
Author: Iaroslav Pyshakov
Year: 2022
Supervisors: Dr. Einar Jón Ásbjörnsson, Dr. Gunnar Skúlason Kaldal
Abstract:
Development of geothermal energy has been constantly advancing over the past few decades contributing to renewable solutions to counteract global changes caused by fossil fuels and power intensive industry. The drilling operation may be one of the most challenging parts in harnessing geothermal energy. Drilling has been done widely across the world and a lot of drilling issues have been faced. Deep geothermal drilling, with the well´s depth more than 2.5 - 3 km, is extremely difficult, e.g. due to chemical composition of deep fluids, high temperature and pressure conditions.
The main objective of this MSc project is to design and calculate main parameters of a deep well, which may be theoretically drilled in the Hengill geothermal area. The planned well is vertical with total depth of 5000 m. In the design of well, emphasis is on casing design, material selection and cementing solutions. New Zealand´s code of practice for deep geothermal wells (NZS 2403:2015) is the main source to achieve objectives of this project. In some cases, the code needs to be extended a due to its design limits. Therefore, special design solutions are implemented in some sections of this project. Pressure and temperature conditions at depth, exceeding the critical point (CP) for water, are based on three scenarios where the maximum possible temperature and pressure of the well 525°C and 240 bar. Another uncommon issue is the wellhead design, where a special class of wellhead is needed out of the scope of the pressure classes included in NZS 2403:2015.
Analysis of data that was obtained during preparation of this project has shown that downhole conditions are challenging reaching beyond the CP at superheated or supercritical conditions. Possible drilling issues have been predicted to be avoided properly. Necessary sizes, materials and length have been chosen for casing and drill strings. Bentonite mud and water with polymers will serve as good coolant and cleaning agents. API G-type cement will create essential bond of casing and walls. Therefore, the deep well, potentially located in the Hengill volcanic complex or in the area with identical conditions, can be successfully drilled building on the presented drilling program using proper drilling equipment and relying on efficient well testing procedures, measuring and logging tools.
For further studies, the possibility of drilling deep geothermal wells into supercritical conditions should be studied further where some sections of this thesis can be a good basis for a proper research study. To summarize, deep geothermal wells have a potential to improve the productivity of drilling operations and a chance of replacing several conventional depth wells by drilling one deep well. However, for that to be viable, several challenges need solutions, e.g. casing, wellhead, drilling fluid, cementing programs should be designed properly.