Faults and rock mechanics. Geological/geotechnical investigation of faulted limestone with permeability

Five chalk types, representing two outcrop localities: Stevns and Hillerslev, and three reservoir zones: Tyra Maastrichtian, Valhall Tor and Valhall Hod, are investigated. Different test types and procedures are applied in small and large scale on various geological featurs i.e. natural and induced fracturs, styloties, bedding planes, and healed fractures from conjugate shear with regards to influence on strength and stiffness. The Hillerslev quarry near Thisted in NW Jutland is chosen as the outcrop locality for special description with respect to fracture occurrence for comparison with reservoir fracture studies. Conclusions: A) The type and degree of cementation should be accounted for when chalk from different localities are divided into groups that are expected to represent similar geotechnical properties. B) The studied chalk types are divided into three main groups: 1. Stevns, Hillerslev and Valhall Tor. High porosity, low degree of cementation. 2. Valhall Hod. Low porosity, low degree of cementation. 3. Tyra. Low porosity, high degree of cementation. C) Hillerslev and Stevns can be regarded as close analogues to the Valhall Tor formation but neither to Valhall Hod nor to Tyra formations. D) Compressive strength is reduced by initial fractues, while stiffness seems to be unaffected. The differences diminish with increasing confining pressure. E) The degree of initial fracturing can be related to the strenght reduction in multiple triaxial testing. F) An effect of scale is observed on Stevns chalk from comparison of tests on block and element specimens. The block specimens have smaller strength but the difference decreases with increasing confining pressure. The planned phase 2 should have special emphasis on naturally fractured Hillerslev chalk oriented according to the global fracture pattern. The statistical variation and the influence of cementation on properties should be tested in small scale. The failure criterion and the K_0 stress path should be tested in both small and large scale. Reservoir chalks should be tested for influence of stylolites and of fractures evaluated from image logs. All specimens should be described before and after testing