This paper presents results of direct shear tests on two types of shales; Rurikfjellet from Svalbard, Arctic Norway and Draupne from Ling Depression, the North Sea. Rurikfjellet formation is part of a caprock system for the proposed CO2 storage site at Svalbard. Draupne shale forms the caprock for deep hydrocarbon reservoirs and also the primary seal for Smeaheia, a candidate site for CO2 storage in the North Sea. Four specimens from Rurikfjellet and one specimen from Draupne were tested. Results of the tests shows that the peak friction coefficient for fractures in Rurikfjellet specimens varies between 0.26 and 0.29 while the residual friction coefficient ranges from 0.19 to 0.25. For Draupne shale, peak and residual friction coefficients were equal; i.e. 0.25. Simulation of friction coefficient was performed using the Barton-Bandis model and showed relatively good results in the post-peak and residual parts. The results of these tests provide reliable input data to support analytical and numerical models for assessing stability of fractures and faults under various loading conditions.
Fractures and faults play a key role for mechanical instability and hydraulic properties of geological formations. Mechanical and hydraulic properties of fractures are among the less known parameters because standard rock mechanical programs usually do not include testing fractured rock samples. A more dedicated test method for measuring fracture properties is the direct shear test which can measure properties of pre-fractured samples for different applications [1-8]. Majority of the available literature on direct shear tests have used rocks other than shale, e.g. synthetic composite blocks, granite, limestone, onyx marble and travertine. The focus of this study is on two types of shale samples; i) Rurikfjellet from Svalbard, Arctic Norway and ii) Draupne from the North Sea. Rurikfjellet is a clay-rich while Draupne is an organic-rich shale. Therefore, these two types of shales were selected for this study to compare frictional properties of shales with high versus low organic carbon content.
Rurikfjellet is a clay-rich shale overlying a reservoir unit that was supposed to be a CO2 injection pilot site at Svalbard, Arctic Norway. There are several publications on characterization of geological, geophysical and mineralogical properties of Rurikfjellet formation [9-11]. There are also a few publications on the mechanical properties of this shale [12-13]. Majority of these studies focus either on field scale properties or on small intact samples subjected to simple mechanical testing such as uniaxial compression and indirect tensile tests. However, shear strength properties for these shales are not available in the literature. Draupne formation is the cap rock for petroleum reservoirs in the North Sea and also the immediate cap rock for Smeaheia candidate site for CO2 storage, offshore Norway. Although some mechanical tests have been done on Draupne shale, there are not enough test data to assess its hydromechanical and sealing capacity. This paper focuses on the determination of frictional properties of pre-fractured shale samples from Svalbard and the North Sea.
