Integrity of Drilling Fluid As Primary Barrier for CCS Wells

The primary barrier in the well during drilling is the drilling fluid, both in terms of hydrostatic pressure from the fluid column, its frictional pressure drop resistance and the influence from the drilling fluid for mitigating reservoir fluid influx. Accordingly, it is of crucial importance that threats to this barrier are understood. When drilling infill wells for carbon capture and storage (CCS), a potential threat to this barrier is the risk of influx of already stored CO₂ from the formation. This is a situation that must be understood as the geological storage of CO₂ is scaled up in order to contribute to achieving climate goals.

While there is substantial experience and knowledge in the industry on interactions between natural gas and drilling fluids, far less is known about the effects of CO₂ of the drilling fluids and how this affects the barrier properties of the fluid. In order to increase the understanding of the risk of primary barrier collapse, laboratory studies of drilling fluids exposed to CO₂ are performed. Challenges to the primary barrier integrity and possible mitigations are discussed in light of the results.