An experimental study on mechanical behaviour of siltstone under brine saturation

Hydro-fracturing process depends on many surrounding factors including overburden stress, confinement, injection flow rate, strength of rock, saturation medium, degree of saturation and mineral composition of the rock. Apart from these, in-situ mechanical properties of the reservoir also highly influences the fracking process, which however may significantly vary with the pore fluid concentration due to the associated brine-rock interactions creating rock structure re-arrangements. This study has therefore been aimed to investigate the effect of pore fluid (brine) concentration and degree of saturation on mechanical properties of tight reservoir rocks. Siltstone samples obtained from the Eidsvold in Queensland, were tested for unconfined compressive strength (UCS) after varyingly saturating them (03 brine concentrations; 10, 20 and 25% NaCl at 04 saturation levels; 25, 50, 75 and 100%). Findings indicate reducing trend of siltstone’s mechanical strength with increasing degree of saturation and an inverted U-shaped variation of siltstone’s strength with increasing NaCl concentration.