Project Description
Well integrity plays a fundamental role in ensuring safe and sustainable subsurface operations, with cementing being essential for maintaining zonal isolation and preventing unwanted fluid migration throughout the well lifecycle. The role of well cementing has evolved significantly beyond its conventional application in oil and gas production wells. Today, cement barriers are increasingly required for CO₂ capture and storage (CCS) and underground gas storage, including hydrogen. Unlike conventional production wells, these applications demand reliable containment over extended periods while exposing the cement to reactive fluids, cyclic injection and withdrawal, pressure and temperature variations, and changing mechanical stresses. These conditions introduce new challenges related to cement degradation, permeability, cracking, and loss of cement–casing or cement–formation bonding, making long-term cement integrity a key research focus. In CCS wells, the interaction of CO₂ with water forms carbonic acid, initiating reactions with calcium-bearing cement phases and progressively altering the cement mineralogy and microstructure. The resulting dissolution, leaching, and possible secondary mineral precipitation can modify porosity and pore connectivity, potentially affecting the mechanical strength and structural stability of the cement. From a transport perspective, these reactions can either enhance leakage pathways through increased permeability and diffusivity or, under favourable conditions, promote self-sealing/self-healing through mineral precipitation within pores and microcracks. For underground hydrogen storage, cement integrity faces a different set of challenges. Unlike CO₂, hydrogen is less chemically reactive with hydrated cement phases, while its small molecular size and high mobility raise concerns regarding diffusion and permeation through the cement matrix and existing defects. Repeated injection and withdrawal cycles introduce pressure and stress fluctuations that may promote microcracking, debonding, or the development of microannuli at cement interfaces, potentially increasing gas transport. In addition, interactions between hydrogen, formation fluids and cement phases may contribute to long-term material alteration. Evaluating cement integrity for CCS and hydrogen storage requires an integrated assessment of its microstructural, transport, mechanical, and interfacial behavior. Microscopic analyses can reveal degradation, mineral precipitation, and microcracking, while permeability and capillary breakthrough pressure measurements under varying pore pressure, temperature, and overburden stress can characterize the cement’s sealing and transport properties. At the well scale, cement–casing bonding and scaled-down well configurations can be used to investigate debonding, microannulus formation, and potential leakage pathways under representative pressure conditions. These investigations can be further combined with cyclic pressure and mechanical loading to reproduce repeated injection–withdrawal operations and assess the long-term integrity of the cement barrier.
Funding
Transformation des Energiesystems Niedersachsen (TEN.efzn)