Investigating Stress Path Hysteresis in a CO2 Injection Scenario Using Coupled Geomechanical-fluid Flow Modelling

Abstract

A successful CO2 storage project will require large volumes of CO2 to be injected into storage at industrial rates in a reliable and secure manner, the operators of the project must also be able to demonstrate the accuracy of modelling predictions for storage to both the regulators and public. Leakage from storage will compromise both the capacity estimates of the storage capacity, and the perceived security of the project even if the leakage is transient. Fluid induced fractures caused by injection of CO2 above the fracture pressure of the formation will control the volume of CO2 a storage reservoir can hold, and will control the rate of CO2 injection; therefore the estimation of the pressure at which a formation will fracture is a key consideration in the modelling of a storage project. Field evidence of fracture pressures from reservoirs in the North Sea show evidence that the fracture pressure upon reinjection into a field is often lower than predicted by conventional approaches. This study presents a coupled geomechanical-fluid flow model modeling injection into a depleted field, the model exhibits hysteretic stress path behavior demonstrating a case of potential overestimation of fracture pressure. This study is the initial stage in a full sensitivity analysis of the material model parameters controlling stress path hysteresis including model geometry effects.