Experimental investigation of the primary and secondary creep behaviour of shale gas reservoir rocks from deep sections of the Cooper Basin

Abstract

This paper investigates the mechanical properties of shale gas reservoir rocks from deep sections of the Cooper Basin with a focus on the creep deformation at high stress and temperature conditions. Rock samples are collected from depths greater than 3000 m in Nappamerri Trough of the Cooper Basin and a series of deformation as well as creep tests were carried out using a triaxial apparatus under simulated reservoir pressure and temperature conditions. Creep tests were conducted at different axial stresses for different durations. The results of this study show that temperature and differential axial stress (a difference between axial stress and confining stress) have significant bearing on the shales' mechanical properties, including creep deformation behaviour. A number of models developed by different authors were used to analyse the experimental data (creep deformation). It has been found that none of these models can adequately describe the creep behaviour of shale gas reservoir rocks from deep sections of the Cooper Basin. In this study we have revised the power-law model and incorporated Arrhenius factor (equation) to account for temperature effect on creep behaviour of shale gas reservoir rocks. The revised power-law model is used to simulate wellbore deformation of the Roseneath, Barnett and Eagle-ford shales at the Cooper Basin temperature and pressure conditions. The results show that the Barnett exhibits little viscoelastic deformation over time while Eagle-ford exhibited twice and Roseneath 180% as much as its instantaneous elastic response over a 24 h period.