The Early Jurassic (Toarcian) Shales in Northern Europe are investigated as possible unconventional sources for gas, where gas in shales is trapped in poorly connected micro pores and is sorbed within particles of organic material and clay minerals in the matrix of the host rock. Having a dual permeable medium consisting of a high permeable fracture network together with a tight shale matrix will improve gas flow rates from matrix to well. The Whitby Mudstone is currently outcropping on the Yorkshire coast hence getting sufficient sample material for permeability experiments is easily available, in combination with mapping of the natural occurring fractures in the cliffs and pavements along the coast this area is an ideal natural analogue to investigate matrix characteristics in combination with the natural fracture network. The studies show that fracture spacing on average is in the order of 10 centimeters and that in combination with a matrix permeability of 1∙10-18 m2 results in gas residue times in the matrix in the order of hours to tens of days depending on the input parameters used.

We studied the rock mechanical behaviour of the outcropping Whitby Mudstone Formation shales (Toarcian Age) under varying temperature and confining pressure conditions, focusing on strength and elastic moduli. We compared the rock mechanical properties of the Whitby shale to published data of time and depositional equivalent shales from Northern Europe and producing shales from the US. We performed uniaxial and triaxial tests in order to constrain the effect of temperature and pressure on the mechanical behaviour of the shale. We loaded the samples normal to the bedding plane under room humidity conditions. We performed uniaxial tests at room temperature and zero confining pressure, whereas we applied confining pressure in several steps up to 50 MPa and considered temperature values between 20-150°C during triaxial tests. Ultimate strength and elastic moduli are strongly influenced by mineralogy, temperature and pressure. An increase in temperature enhances the deformability, whereby the Young’s Modulus and ultimate strength decreases. With an increase in confining pressure, Young’s Modulus and ultimate strength increases, whereas the Poisson’s ratio decreases.