Abstract
It is crucial to ensure that stored CO2 does not leak into the atmosphere. As the last step in the Carbon Capture and Storage (CCS) process, CO2 is injected into underground formations, and it should remain stored there for eternity. However, when reusing old petroleum wells for CO2 storage, defects in the cement sheath, such as microannuli or radial cracks, might be present from production operations such as shut down/startups or from the injection process itself. Thus, causing a possible leak path for CO2 through the cement. Upon reaction with CO2 the cement carbonates, and this carbonation process may in fact seal the cracks in the cement. This so-called self-healing effect has been studied experimentally for many years, but, to the best of our knowledge, none of these studies were performed with realistic well geometries with cracked cement sheaths.
An advanced experimental setup has been developed to study the sealing process of realistic cracks in the cement sheath by flowing CO2 through radial cracks and investigate the effect of flow rate and exposure time for different cement systems. The setup consists of a modular based downscaled section of a wellbore with rock, cement, and casing, and allows for a confining pressure up to 100 bar around the rock. Pressure cycling experiments are performed on the cement sheath by increasing the pressure from inside the casing, causing realistic radial cracks in the cement sheath. When these cracks are connected axially through the sample, they provide a leak path for fluids through the cement. This novel setup allows for a direct exposure of the bottom of a microannuli or radial crack with CO2, and thus measure the flow through the cracks and study the possible healing effects by CO2. The novelty of the setup lies in a movable support of the cement sheath. The first position allows a firm support for the cement upon curing, and the second, at a lower level opens the ports for CO2 exposure and exposes the full bottom surface of the cement sheath. The cracks in the cement sheath were visualized using μ-CT both prior to and after CO2 experiments.
The paper describes in detail the novel laboratory setup and the applicability of the setup.
An advanced experimental setup has been developed to study the sealing process of realistic cracks in the cement sheath by flowing CO2 through radial cracks and investigate the effect of flow rate and exposure time for different cement systems. The setup consists of a modular based downscaled section of a wellbore with rock, cement, and casing, and allows for a confining pressure up to 100 bar around the rock. Pressure cycling experiments are performed on the cement sheath by increasing the pressure from inside the casing, causing realistic radial cracks in the cement sheath. When these cracks are connected axially through the sample, they provide a leak path for fluids through the cement. This novel setup allows for a direct exposure of the bottom of a microannuli or radial crack with CO2, and thus measure the flow through the cracks and study the possible healing effects by CO2. The novelty of the setup lies in a movable support of the cement sheath. The first position allows a firm support for the cement upon curing, and the second, at a lower level opens the ports for CO2 exposure and exposes the full bottom surface of the cement sheath. The cracks in the cement sheath were visualized using μ-CT both prior to and after CO2 experiments.
The paper describes in detail the novel laboratory setup and the applicability of the setup.