The Swedish research infrastructure for scientific drilling ”Riksriggen"

Riksriggen

ICDP is an international research infrastructure with Swedish participation. Riksriggen’s collaboration with ICDP, which includes operational support, material and trans-national access.
In 2012, VR awarded Prof. Maria Ask a grant for developing and building a downhole stress measurement system. This infrastructure belongs to Luleå University of Technology and is a very important asset for the entire scientific drilling community because it is unique in three aspects: (1) It can conduct stress measurements to 3 km depth; (2) it can operate in all borehole sizes that can be drilled by Riksriggen; and (3) it provides a full borehole resistivity image. Borehole logging with an acoustic borehole televiewer is essential for working with in-situ stress measurements. Such a sensor is part of Riksriggen’s logging system.

The Swedish national research infrastructure for scientific drilling “Riksriggen” is a versatile instrument for multidisciplinary subsurface research with a core drilling and testing capacity to 2.5 km depth. Main questions to be addressed by the infrastructure concern the evolution of the Earth's crust and processes ongoing within it at present, for example, mountain building and earthquakes. The infrastructure can also address societal challenges such as natural resources, natural hazards, underground construction and waste disposal. Geological samples recovered by the infrastructure are used to study topics such as the deep biosphere, chemical composition of rock and fluids, quality and quantity of groundwater resources, storage and extraction of geothermal energy, storage of nuclear waste or CO2, identifying risks with deep mining. Riksriggen serves the Swedish drilling community through the entire life-cycle of scientific drilling and provides qualified support for the technical use of the infrastructure, both advisory and operational.

Riksriggen is a modern wire-line core-drilling rig that complies with latest safety and environmental regulations. The Atlas Copco Christensen CT20C drill rig can handle three common hole/core sizes P, H and N (123/85 mm, 96/63 mm and 76/48 mm hole/core diameter, respectively) and has a depth capacity of around 1050 m, 1600 m and 2500 m, respectively (assuming a vertical water-filled hole). The rig is crawler mounted and equipped with a data acquisition system for monitoring and recording operational parameters, which is special designed by Lund University.
In-The-Hole equipment includes complete core retrieval systems for P, H and N-size cores including PHD, HRQ V-Wall and NRQ V-wall drill rods in sufficient length to cover the maximum drilling depth for each size. Both dual and triple tube core assemblies are accessible for each size. Other equipment belonging to the infrastructure are, amongst others, a mud cleaning and mixing system, cementing equipment, fishing tools, well heads and a blow-out preventer (BOP).The infrastructure is complemented with a fully-equipped workshop container with an integrated 2.2 m3 diesel tank and a terrain-going truck with a crane and hook-system for equipment transport.
Furthermore, an advanced hydraulic testing system
with single/straddle wireline packers in all three dimensions, pressure sensors and submersible pumps is part of the infrastructure. The geophysical borehole measurement system, necessary for obtaining as complete borehole information and documentation as possible, consists of nine probes: electrical logs, caliper, formation density, acoustic and optical televiewers, full waveform compensated sonic, fluid conductivity and temperature. The logging system has a cable capacity of 3000 m, but the majority of the probes have a pressure rating of 20 MPa. A gas and fluid sampler is also available.

A drilling project generates a large amount of data that can be subdivided into two groups. (i) Data that originate directly from the research infrastructure, such as drill cores, technical parameters that are acquired by the rig’s data acquisition system and the drilling personnel during the operations; and the scientific documentation of the borehole with logging probes, which is also done by Riksriggen personnel. (ii) Data that are acquired by the scientific project, such as core descriptions, geochemical and geophysical core logs, images, chemical composition of gases, and more. (i) and (ii) together are the essential basis for the scientific research but do not constitute scientific novelties on their own.

Qualitative drilling and sampling to depths down to 2500 m, by using continuous core drilling. Subsequent hydraulic testing and in-situ measurements, such as geophysical borehole logging, and fluid sampling in the borehole. Riksriggen serves the Swedish drilling community through the entire life-cycle of scientific drilling and provides qualified support for the technical use of the infrastructure, both advisory and operational. This service includes the provision of expertise with regard to the planning, design and conduction of core drilling operations and subsequent downhole surveys and testing. All support is adapted to the users’ expertise and thus, also fits scientists who do not have previous knowledge about drilling, a specific instrument or a certain method that is required to conduct their research.

Engineering Geology is managing and operating the infrastructure. Members of the Riksriggen's consortium are LU, UU, LTU and LNU. The steering committee consists of one representative and one proxy for each of the consortium partners.