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Keywords:

  • CO2 geological sequestration;
  • uncertainty quantification;
  • sensitivity analysis;
  • reduced-order model

Abstract

A series of numerical test cases reflecting broad and realistic ranges of geological formation properties was developed to systematically evaluate and compare the impacts of those properties on pressure build-up and ground surface displacement and therefore risks of induced seismicity during CO2 injection. A coupled hydro-geomechanical subsurface transport simulator, STOMP (Subsurface Transport over Multiple Phases), was adopted to simulate the migration of injected CO2 and geomechanical behaviors of the surrounding geological formations. A quasi-Monte Carlo sampling method was applied to efficiently sample a high-dimensional parameter space consisting of injection rate and 12 other parameters describing hydrogeological properties of subsurface formations, including porosity, permeability, entry pressure, pore-size index, Young's modulus, and Poisson's ratio for both reservoir and caprock. Generalized cross-validation and analysis of variance methods were used to quantitatively measure the significance of the 13 input parameters. For the investigated two-dimensional cases, reservoir porosity, permeability, and injection rate were found to be among the most significant factors affecting the geomechanical responses to the CO2 injection, such as injection pressure and ground surface uplift. We used a quadrature generalized linear model to build a reduced-order model that can estimate the geomechanical response instantly instead of running computationally expensive numerical simulations.