Luleå University of Technology has received funding for national infrastructure from the Swedish Research Council to build a national resource for rock stress measurements. The equipment is unique in the world and allows three-dimensional rock stress determination down to 3 kilometer deep boreholes.
It will primarily be used in projects that are generated within the Swedish Scientific Drilling Program (SSDP) and the International Continental Drilling Program (ICDP), but it will also be used in more applied projects.
Several types of applied projects
The state of stress affects the rock mass stability and permeability. Therefore, knowledge about the state of stress is of the great importance for the vast majority of rock engineering projects at greater depth.
– This knowledge is important for several types of applied projects, such as the analysis of the safety of the repository of spent nuclear fuel, geothermal energy, carbon dioxide storage in bedrock and stability calculations for various types of manmade underground structures, says Maria Ask, Professor of Applied Geology at Luleå University of Technology.
3 kilometer depth into bedrock
Daniel Ash, Adjunct Professor in Exploration Geophysics Photo: Tomas Bergman
– The technology we use downhole called hydraulic fracturing. With a pair of seal packers we part of the borehole. Then we pump carefully into water under high pressure and measures the pressure when the rock wall cracks or an old crack open. Using a electrical imager then we measure the crack orientation, says Daniel Ask, professor in exploration geophysics at Luleå University of Technology.
The rock stress measurements equipment consists of two main parts, measuring equipment in the borehole and data collection device on the surface. Three versions of the instrumentation in the borehole is being constructed to enable measurements in three different borehole diameters, 122, 96 and 76 mm. The challenge is to design the measuring devices so it fit in the slim boreholes while being robust enough. Above ground, the surface system is installed in a steel container that is mounted on a 13 meter long trailer. The container also holds three winches which have 3 km long steel tubing and logging wire that connects the borehole equipment with the surface system.
The sensor sends the data from the borehole at 3km deep.
The equipment is being built at the university
Most of the equipment in the borehole built at Luleå University of Central workshop but the project also includes a research collaboration with the University of Strasbourg in France.
– I have worked here at the central workshop since 1973 and this is the biggest task I have experienced, all categories. There is also a project where all of our skills and experience will be tested and challenged, says research engineer Tommy Nilsson, Luleå University of Technology.
Geosciences and Environmental Engineering division at the Luleå University of Technology
13th of April 2016