Coupled Thermo-Poro-Elastic modeling of near wellbore zone with stress dependent porous material properties

Abstract

In this study, the Thermo-Poro-Elastic approach was applied to investigate the dynamic shear and tensile failure condition in the near wellbore zone. The necessary data to perform the analysis were collected from literature. To increase the simulation accuracy, the stress dependency of the material properties such as porosity, permeability, bulk density, bulk compressibility, bulk heat capacity, bulk thermal expansivity, bulk thermal conductivity, and Biot's poroelastic coefficient was also considered. The coupled study was conducted with cool, isothermal, and hot wellbore fluid to investigate the temperature influence. The obtained results were compared with the results of the uncoupled static approach. The computations take into account the changes in material properties due to the stress alteration in near wellbore zone. Results revealed that the pore pressure in the near wellbore zone was very sensitive to the wellbore fluid temperature which consequently influences the dynamics stress distribution in the studied near wellbore zone and its stability state. For the first case, when wellbore fluid temperature was lower than the formation temperature, shear strength decreased abruptly at the early time steps and then increased to a steady value, which is equal to the shear failure stress estimated by the uncoupled approach. The estimated tensile strength was high originally and descended to the value estimated by the uncoupled approach at infinity. In the isothermal and hot wellbore fluid cases, an abrupt change occurred in the shear strength; however, for hot wellbore fluid, the shear strength then decreased permanently with a slope depending on the wellbore fluid temperature. At the first step of modeling for all three cases, the initial tensile strength was the same. When formation rock was exposed to a cool wellbore fluid, tensile strength was maximum at initial stages and then decreased to the estimated value by the uncoupled approach. Rising wellbore fluid temperature causes an initial tensile instability shock (decrease in tensile strength) vanishing by time. Based on the results, average principal stress distribution in near wellbore zone intensely alters permeability distribution. The sensitivity of other parameters is less than permeability and can be neglected in further studies.