CO2 Injector Integrity: The Comparison of Semi-Analytical Solution with FE Analysis of Near Wellbore Thermo-Poro-Elasticity Couplings

Abstract

Abstract Depleted gas reservoirs in the North Sea offer an interesting potential for CO2 storage because the geology is understood and the infrastructure is in place. One of the key issue is to check that the wells which have been producers during the life-time of the reservoirs can now be used safely for cold gas injection. This paper contributes to this question by providing a workflow to analyse the possible failure and debonding between the casing and the cement during the injection phase. A classical analytical solution based on thermo-poroelasticity is proposed, assuming a vertical well, an axisymmetric stress distribution, and either plane strain during gas production, or plane stress during injection. This simplified solution is compared with the predictions of a commercial 3D finite-element (FE) code applied to the near well regions. The application concerns a well in a reservoir, off-shore The Netherlands. The analytical solution, easy to develop, is found to be of great help in shedding light on the FE predictions, which involves detailed but complex process to arrive at the solution. The integrity analysis is performed after completion, at the end of depletion and during CO2 injection. The analytical solution predicts debonding at the casing-cement contact and shear failure hazards in the cement, which are not identified with the numerical tool. This paper provides valuable insights into the application of numerical and analytical solutions, pros and cons for both approaches are discussed considering computation cost and setting up of the model.