Experimental study on the geomechanical properties and failure behaviour of interbedded shale during SAGD operation

Abstract Interbedded shale (IBS) impedes the development of a steam chamber and poses a serious threat to the success of any steam-assisted gravity drainage (SAGD) operation in a heavy-oil reservoir. Breaking up IBS has been a continual challenge for the industry. This study summarizes experimental studies on the geomechanical properties and failure behaviour of IBS during thermal stimulation. IBS cores were collected by means of fully sealed coring in northwestern China. Mineral composition analysis, porosity, and permeability measurement, as well as imbibition tests, were initiated to evaluate the potential of imbibition. First, shear failure behaviour was studied through triaxial compression tests. Second, pore structure and failure processes of IBS were investigated through thermal stimulation experiments. Mudstone IBS was considered as the focus. Its porosity was approximately 7% and permeability was approximately 100 nD while in-situ stress was applied. Although IBS contained considerable smectite components, it didn’t disintegrate under high-effective stress. Last, shear failure behaviour of IBS was observed by computer tomography (CT) scanning when IBS was heated up to 180 °C under constant radial confining pressure and axial constraint of strain. While imbibition causes disintegration of IBS, it is unlikely when under in-situ stress conditions. Fortunately, shear failure can be achieved under uniaxial boundary conditions with rapid heating.