CO2 INJECTION IN ANTICLINE RESERVOIRS: STRUCTURAL INFLUENCES ON MAXIMUM SUSTAINABLE PORE PRESSURE AND SEISMICITY RELATED TO FAULT REACTIVATION

Anticline structures are one of the most common structural traps for hydrocarbon reservoirs and are thus becoming prime targets for geologic CO₂ sequestration into saline formations. The injection of CO₂ into geologic formations increases the formation pore pressure and induces geomechanical risks such as fracture reactivation or the generation of new fractures. This will result in seismicity and lastly generate preferred fluid flow pathways along which dissolved CO₂ may escape into the atmosphere. In order to assess these geomechanical risks a thorough simulation coupling fluid flow through porous media and geomechanics of a realistic representation of the formation of interest is required.

In this study we use a one-way coupling approach transferring pore pressure results from a reservoir simulator to geomechanical models using finite element analysis. From the mechanical finite element models, we initially determine the maximum sustainable pore pressure before CO₂ injection. Our geomechanical models show that structural parameters such as anticline amplitude and wavelength, layer thickness and intra-bedding friction under various stress regimes have a significant impact on the maximum sustainable pore pressure in the reservoir.

After injection we study the spatial and temporal CO₂ plume evolution in the reservoir and transfer the resulting pore pressures back to the geomechanical models. We include a preferably oriented fault in the model and propose 2 procedures to simulate fault reactivation. Our models show that CO₂ induced pore pressure increase can trigger reactivation of pre-existing structures and based on the resulting fault slip the resulting seismic magnitudes can be estimated.