A Nonlinear Elastic Model for Oil Sands Considering Shear Dilation and Strain Softening

The oil sands mechanical model is the foundation of petroleum engineering design and development. Describe more precisely the shear dilation and strain softening characteristics of oil sands, this paper proposed four-parameter models about the relations of axial strain-deviatoric stress and axial strain-volumetric strain. The four-parameter models, Nanshui Model, and the modified Chengdu Science and Technology University (CSTU) Model were compared to analyze their fitting effects on the test data of axial strain-deviatoric stress and axial strain-volumetric strain for Fengcheng oil sands. Lastly, the four-parameters models and the modified CSTU Model were used to predict the increase of shear dilation-induced absolute permeability and the effective permeability to water. The research shows that the four-parameter models can describe the strain-softening behavior, shear dilation effect, and volumetric strain evolution much better than the modified CSTU Model. The shear dilation-induced increase of the absolute permeability and the permeability to water can be predicted more accurately according to the four-parameter models, whose prediction error is even more than 50% lower than the modified CSTU Model. The four-parameter models proposed in this paper can provide an important basis for the well drilling, well completion, and the numerical simulation of thermal stimulation in oil sand reservoirs.