Thermo-poroelasticity under constant fluid flux and localized heat source

Abstract

Coupled thermo-hydraulic-mechanical behavior of saturated porous media with low permeability is of crucial significance to multiple operations including thermal treatment for declogging wellbores, thermal fracturing during production of unconventional shale oil, radioactive-waste disposal, and soft tissue and tumor growth. This work presents new thermo-poroelastic solutions for an isotropic medium subjected to a constant fluid flux and a localized heat source, incorporating two novel components: (a) transient flow transfer between the source and the embedding layer, thus incorporating the temporal thermo-poroelastic changes in the stress state adjacent to the source; and (b) vertical confinement effects on the mechanical response of the target zone, governed by the stiffness of the sealing media using the Winkler model approximation. The Westerly Granite is selected to assess the thermo-poroelastic alterations induced under the imposed fluid flux and heat loads. Results reveal generation of short-term thermal-induced pore pressures subsequent to injection initiation which otherwise cannot be predicted using current solutions. The new solutions capture higher thermal induced pore pressures and a more rapid dissipation under a higher heat transition rate between the source and the target zone. A compassion between the response of the porous layer under constant fluid flux and localized heat source, versus localized heat and flow sources reveals the former loading to be the most effective for localized thermal treatment as it results in: notably higher thermal-induced pore pressures, the maximum thermal-induced pressures to occur in the source vicinity; and particularly slower dissipation of the thermal-induced pore pressures. The stress paths demonstrate slight initial dilation before compaction under the latter loading; while the former results in an initial compaction with higher deviatoric stresses proceeded by dilation once the thermal-induced pore pressures tend to dissipate. Stress paths reveal the vertical confinement to remarkably impact the response of a porous layer. Higher compaction is generated under higher vertical confinement. In case of a mechanically free source-medium interface, lower vertical confinement gives rise to higher deviatoric stresses and lower mean stresses during the initial compaction phase, in addition to causing the formation to undergo dilation much sooner compared to when higher confinement is applied. For a mechanically fixed boundary setting, higher deviatoric stresses are generated under higher vertical confinements.