Predicting Dynamically Evolving Permeability and Localization of Fluid Flow in Underground Waste Storage Operations

Large amounts of CO2 and other waste fluids are being injected into reservoirs all around the world. Preventing leakage of the fluids into sensitive ground water reservoirs and to the surface and assuring safe long terms storage are essential requirements in these operations. One example is the injection of about one million tons of CO2 per year since 1996 into the Utsira formation at Sleipner in the Norwegian North Sea. Conventional reservoir simulations fail to the formation of flow chanels or chimneys, and the fast spreading underneath the caprock. We developed a new numerical code that predicts the formation of chimneys as a consequence of coupled deformation-fluid flow, without prescribing pre-exiting fractures. Our 3D model includs full mechanics and visco-elastic deformation, allowing for simulation of injection into a pre-stressed reservoir. Observations that are used to evaluate our simulation results against resevoir data include pressure at the wellhead, CO2 filled porosity, CO2 flux over time, distribution of CO2 in the reservoir, spreading of CO2 underneath the caprock and pattern (chimney) fomation. Our model helps to understand and explain under which conditions localization of fluid will occure and is also applicable to the injection of other fluids (e.g. waste water).