Fault modelling and geomechanical integrity associated with the CO2CRC Otway 2C injection experiment

Abstract

Structural and geomechanical models of the CO2CRC Otway Project's Paaratte Formation are presented in advance of the proposed Otway Project time-lapse seismic monitoring of plume stabilisation test. The main goal of this experiment is to detect and monitor a CO2 plume in a saline aquifer using 4D seismic techniques and subsequently confirm plume stabilisation. The modelling results show that the likelihood of injection induced fault reactivation is exceedingly small, due to the very small pressure increases associated with injection (∼0.05MPa at the faults after about 100 days of injection). The potential for CO2 flow across the main reservoir-cutting faults was quantified using the shale gouge ratio algorithm. Results indicate that the faults should be sealing to some degree and should therefore restrict the lateral movement of CO2. A dynamic simulation characterizing the potential for CO2 flow vertically through the Naylor South splay fault indicates that a very limited volume of CO2 gas would migrate up the fault. According to dynamic simulations of a deliberately leaky fault, CO2 is only able to migrate 10s of metres vertically after 100 years, which is still more than 350m below the top of the Paaratte Formation. This study is not only important as it provides a peer reviewed workflow for risking a carbon capture and storage (CCS) experiment, but geophysical observations during the experiment will also allow the assumptions and models to be tested in the field and various model parameters to be calibrated. Structures sealed by faults are extremely common for hydrocarbon accumulations, and will also be for CCS, and thus fault modelling will be a vital part of site characterisation.