Thought about Constitutive Model of Oil Sands during SAGD Process

The increase in temperature due to the steam injection during SAGD acts to reduce the elastic moduli of oil sands and may induce shear dilation and consequent permeability increase. This would enhance the steam chamber growth, increasing the efficiency of bitumen production. Motivation of this study is to quantitatively understand the evolution in the oil sand's elastic properties as well as strain-induced permeability increase during SAGD process. Rock physics modeling was conducted for the investigation of elastic properties of oil sand. Assuming pure quarts and bitumen as the two end members, the lower Hashin-Shtrikman bound underestimates the measured P-wave velocity. This indicates that the quartz grains of oil sand are not suspended in bitumen but constitute a load-bearing framework. Based on this observation, we used the soft-sand model and calculated dry-frame elastic properties of oil sands. The effect of the pore-filling bitumen on the elastic properties is quantified by using the solid substitution. The temperature dependent elastic properties of bitumen are obtained from published data. The rock physics model offered here relates the elastic moduli of oil sand to its temperature. Dilation-induced permeability change was discussed by using core measurements of porosity and permeability. Oil sand cores are dilated when they are brought to the surface and released from the confining stress. Porosity and permeability measurements of these samples of dilated sand are cross-plotted versus each other and the theoretical Kozeny-Carman curves are superimposed on these data. This plot indicates that the Kozeny constant varies with strain where porosity is low but remains constant where porosity is high. The purpose of this study is to provide basic understanding of temperature effects on the elastic properties of oil sand and permeability changes during shear dilation to help develop a constitutive model for a prospective coupled geomechanical and fluid flow modeling of SAGD.