Effects of Uncertainties in Fault Interpretations on Pressure Depletion and CO2 Storage Injection at Horda Platform, Offshore Norway

Abstract

Fractures and faults may serve as important barriers or conductors to fluid flow and pressure propagation in the underground. When injecting CO2 into a reservoir for underground storage, the pressure changes in the subsurface can potentially affect large areas, depending on reservoir characteristics and injected volumes and rates. Similarly, production of fluids (i.e. oil and gas production) can have a far-reaching influence on pressure and knowledge about the existence and properties of faults and fractures is important for understanding and controlling pressure in CO2 injection projects. In this paper, we focus on testing how the sealing properties of interpreted faults will affect fluid flow and CO2 injection over production time scale. In particular, we aim to test the effect of the uncertainty in interpretation of relay zones along large fault systems. Simulations have been carried out on a dataset from the Horda Platform and northern part of the Stord Basin, offshore Norway. We address the potential effect of pressure depletion in the Troll oil and gas field on the Smeaheia area which has been considered for CO2 underground storage. This is done by varying the sealing properties of the faults and by testing the effect of assuming extended faults in two relay zones along the N-S striking Vette Fault System. Reservoir simulations show that assuming sealing relay ramp structures will have a major impact on pressure development in the target injection area caused by the pressure depletion in the Troll Field and the injection of 150 Mt CO2 in Smeaheia. With sealing relay zones along the Vette Fault, the pressure in the Smeaheia area will be higher and less affected by the Troll Field depletion, and thereby the gas plume and gas saturation will affect a smaller area, compared to assuming open or semi-sealing faults.