ANISOTROPIC CHEMO-POROELASTICITY WITH ION TRANSFER

Abstract eng:
This paper presents a linear chemo-poroelastic model for predicting shale deformation in transversely isotropic media. The theory incorporates the stresses and pore pressure with four coupled transport processes of ‡uid and solute: hydraulic conduction, chemical osmosis, chemical solute di¤usion, and pressure solute di¤usion. The ‡uid is considered compressible and consisting of a binary electrolyte solution (solute and diluent). The total stresses and variation of ‡uid content are linearly related to the strains, pore pressure, and solute mass fraction through anisotropic material coe¢cients. The …eld equations are constructed for solid displacements, pore pressure, and solute mass fraction by implementing the rock constitutive relations and transport equations into the momentum and ‡uid and solute mass balance equations. The resulting Navier-type equations couple the elastic strains to the pore pressure and the solute mass fraction. The other …eld equations express the couplings of the ‡uid and solute di¤usions with the elastic strains. To show the impact of the physico-chemical processes on the pore pressure and stress …elds around a wellbore, an example of a vertical well drilled in an isotropic shale formation is presented. Results indicate that although the osmotically-induced reduction in the pore pressure tends to stabilize the borehole, ion di¤usion into the formation can cause the formation to fail in tension.

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