Swelling of shale around a cylindrical wellbore

Abstract

A modified form of Biot’s linear theory of poroelasticity is applied to shale swelling in contact with an aqueous electrolyte. The shale is assumed to behave as an isotropic, perfect ion exclusion membrane, and in this limit swelling depends only upon the total stress and on the chemical potential of water within the pores of the rock. An axisymmetric, plane-strain analysis of swelling around a wellbore is first presented, and this is subsequently extended to include swelling of a cylindrical hole in a finite, cylindrical shale sample. It is predicted that swelling is prevented if the chemical potential of water within the shale equals that within the wellbore. The predictions of the analysis are compared with experimental results obtained when drained outcrop shale swelled in contact with aqueous solutions of KCl or NaCl. The experimental swelling did indeed vary with water chemical potential, and could be prevented if the salt concentration within the wellbore fluid was sufficiently high. However, post-mortem chemical analysis of the shale showed that ion-exchange had taken place, with consequent modification of the shale’s mechanical and chemical properties. Ion exclusion was therefore imperfect, and an analysis that incorporates the chemical potentials of components other than water is necessary.

Influence of coupled chemo-poro-thermoelastic processes on pore pressure and stress distributions around a wellbore in swelling shale

“…Poroelastic (Cui et al, 1997) and partially coupled chemo-poroelastic (Sherwood and Bailey, 1994) models have been applied to obtain time dependent stress and pore pressure distributions around a wellbore, and to illustrate the influence of mud salinity. A model was also presented in Ghassemi and Diek (2002) for consideration of the chemical potential in high temperature environments.…”

“…It is well known that hydraulic and chemical osmotic effects cause water to move into or out of the formation (Hanshaw and Zen, 1965;Chenevert, 1970). The latter is driven by the difference in activity between the water in the drilling mud and the formation pore water (Mody and Hale, 1993;Onaisi et al, 1993;Sherwood, 1993;Sherwood and Bailey, 1994;Sharma et al, 1998). In addition to flow and thermal stresses arising from thermally-induced pressurization, a temperature contrast between the drilling mud and the formation also can induce irreversible transport processes when drilling in shale sections namely, thermo-osmosis and thermo-filtration.…”

Anisotropic Porochemoelectroelastic Solution for an Inclined Wellbore Drilled in Shale

“…Simultaneously, the effective stress and strain distributions in the formation are also modified which could lead to detrimental effects on the formation integrity. With increasing shale drilling and fracturing activities for oil and gas production, these coupled chemical-mechanical processes in shale have become lately a topic of extensive research [9][10][11][12]. For example, the isotropic solution of a plane strain wellbore was given in Ref.…”

A Non-Isothermal Constitutive Model for Chemically Active Elastoplastic Rocks

“…They used the non-equilibrium thermodynamic concept in the framework of macroscopic approach to derive their equations. In other attempt Ekbote and Abousleiman (2005) used a different approach, which is based on the extended version of equations of poroelasticity and the work of Sherwood and Bailey (1994) to solve the problem of chemo-poroelasticity and thermo-chemo-poroelasticity in transversely isotropic porous media.…”