Mechanical and Petrophysical Properties of a Calcareous and Bituminous Shale

Bituminous shale – a potential gas shale source in Europe - from cores of 3 different wells and from a quarry was characterized by means of mechanical and petrophysical investigations. The investigated specimens feature a wide range of maturity (0.5-1.4%), porosities (1-11%), and permeabilities (4-550 nD). The uniaxial compressive strength, the tensile strength and p-wave velocity of this shale is anisotropic. The strength normal to bedding planes is up to 50% higher than parallel to bedding and the p-wave velocity differs by 50% as well with an opposite trend. At elevated confining pressures the shale shows a transition from brittle to semibrittle behaviour already at relatively small values (> 50 MPa); this behaviour is pronounced with increasing temperature (≤ 200°C). Mechanical data and microstructural observations reveal that rearrangement and compaction of pores are important for low strain deformation behaviour. A careful characterisation is essential to identify productive horizons in this calcareous and bituminous shale.