A fully coupled finite element framework for thermal fracturing simulation in subsurface cold CO₂ injection

Abstract

Thermal fracturing could occur during cold CO₂ injection into subsurface warm rock formations. It can be seen in a variety of fields such as carbon geo-sequestration, unconventional gas development, enhanced oil recovery, geothermal energy extraction, and energy geological storage systems. In CO₂ geosequestion, limited degree of thermal fracturing due to the cooling effects of cold CO₂ injection will enhance well injectivity, especially for those storage formations of low permeability. Thermal fracturing can therefore potentially enhance the injection efficiency and make positive impact on commercialization of CO₂ geological storage. However, excessively developed fractures could break down the caprock and cause potential CO₂ leakage into overlying rock formations. Risk analysis has to be done based on thermal fracturing simulation in order to maintain caprock integrity.

Simulation of thermal fracturing during cold CO₂ injection involves the coupled processes of heat transfer, mass transport, rock deforming as well as fracture propagation. To model such a complex coupled system, a fully coupled finite element framework for thermal fracturing simulation is presented. This framework is based on the theory of non-isothermal multiphase flow in fracturing porous media. It takes advantage of recent advances in stabilized finite element and extended finite element methods. The stabilized finite element method overcomes the numerical instability encountered when the traditional finite element method is used to solve the convection dominated heat transfer equation, while the extended finite element method overcomes the limitation with traditional finite element method that a model has to be remeshed when a fracture is initiated or propagating and fracturing paths have to be aligned with element boundaries.

Keywords

Poromechanics / Petroleum geomechanics / Thermoporoelasticity / Coupled processes / Thermal fracturing / Cold CO₂ injection

Acknowledgements

The Author gratefully acknowledges the support of Department of Energy (DE-FE0026825).

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