Experimental investigations on elastoplastic deformation and permeability evolution of terrestrial Karamay oil sands at high temperatures and pressures

摘要

Coupled thermo-hydro-mechanical analyses in heavy oil reservoirs are essential for engineers to evaluate and optimize the field operations in terms of safety, economy, and environment during thermal stimulation. The terrestrial Karamay oil sands were used for a series of high-temperature high-pressure triaxial drained compression tests to understand the deformation and flow behaviors at multiple stress, pore pressure, and temperature conditions. This article was dedicated to the experimental investigations on the elastoplastic deformation and permeability evolution of Karamay oil sands under shear and isotropic compressions. The geomechanical conditions of shear dilatancy and tensile parting behaviors were observed, and the phenomena of shear yield and isotropic compression yield of Karamay oil sands were proven during thermal stimulation. All the elastoplastic and flow parameters at different temperatures were determined. The major conclusions can be drawn that the effective confining stress and temperature both have very significant effects on the elastoplastic deformation and flow behaviors of Karamay oil sands. The shear dilation can be more meaningful with a lower effective confining pressure and a higher temperature. A proper shear dilatancy can occur at 100 degrees C both at low and high effective confining pressures. A higher temperature is generally not beneficial to the tensile parting induced volumetric expansion. There are both elastic and irrecoverable plastic deformations under isotropic drained compressions. 70 degrees C is a critical temperature for the elastic property and permeability changes with temperature for Karamay oil sands. The cohesion and friction angle are much lower at a higher temperature, and the cohesion at 100 degrees C is appropriately 0. The cap yield surfaces at different temperatures show little difference. The relation of shear-induced volumetric strain and permeability can be well fitted using a linear function. The permeability improvement declines exponentially with the effective confining stress increasing. The permeability generally rises with the tensile parting induced volumetric strain at all temperatures, and it can be improved much more at a higher temperature. The permeability declines linearly with the effective stress increase in the semi-logarithmic coordinates.