In–situ quantification of mechanical and permeability properties on outcrop analogues of offshore fractured and weathered crystalline basement: Examples from the Rolvsnes granodiorite, Bømlo, Norway

Fractured and weathered crystalline basement units below erosional unconformities potentially represent unconventional reservoirs for georesources (oil, mineral water). The reservoir properties characteristics strongly depend on secondary processes connected to the local structural alteration/weathering history. Here we present results of in–situ field quantification mechanical (uniaxial compressive strength) petrophysical (permeability) a fractured at selected outcrops island Bømlo (western Norway). are believed an onshore analogue oil hosted in offshore Utsira High granodioritic (northern North Sea). off– basements have both undergone surficial weathering during Mesozoic, as shown by occurrence dated, variably thick saprolitic profile top fresh blocks. is characterized complex highly permeable fracture network. Fault rocks within its fault zones characterised anisotropic strength average permeability that two orders magnitude larger than host rock. matrix significantly affected products. Analysis textural mineralogical allowed us constrain variation function increasing alteration infer their distribution the, now eroded, top–basement Bømlo. Weathering enhances drastically decreases strength. Nevertheless, evolved horizons may act low–permeability top–seal reservoir. obtained data finally used better potential rocks, fluid migration pathways, discuss role geomechanics conceptualised