Stiffening and strengthening by increased temperature of dry sandstones from the deep North Sea Basin

With increasing interest in geothermal and high temperature petroleum reservoirs, theories and supporting experimental data capable of describing temperature effects on rock mechanical properties become of increasing importance. Published work on the subject is however limited and scattered on various lithologies and with most work conducted using outcrop material high chance of finding contradictory conclusions and misguided use of temperature trends in evaluation of in-situ reservoir properties stands. For two quartzitic sandstones from the deep North Sea Basin with different petrophysical properties, we designed a testing program with the intension of investigating temperature effects on stiffness and strength properties. We assume that studied reservoir material has never experienced higher temperature than in-situ, because the North Sea basin is geologically undergoing subsidence and hence we derived static and dynamic E-moduli and strength parameters at ambient and in-situ temperature hence envisaging the material’s geological temperature history. Result for both sandstones show higher stiffness and strength at in-situ temperature as compared to ambient, and we propose that thermal expansion of constituting minerals leads to increased frictional forces in grain contacts as a physical explanation of the observed behaviour. Test results illustrate the importance of temperature-controlled experiments for rock physical and rock mechanical modelling.