Abstract
Fluid leakage through abandoned wells may lead to a major release of hydrocarbons or stored CO2 in the atmosphere. To detect potential leakage and assess well and plug integrity, monitoring systems such as optical fibers can be integrated in the well barriers. The placement of optical fibers in cement plugs may however increase the risk of leakage, as it may induce leakage path formation in well barriers. This paper presents an investigation on the risk of leakage path formation by the placement of optical fibers in well barriers, using a laboratory setup, where a cement plug is placed in a 2’’ diameter steel casing. The first tests were performed with a standard Portland G cement without additives, with two optical fibers centered in the plug. Major leakage is measured, and we observed that leakage paths are located at the interfaces: cement-casing interface and fiber-cement interface. However, due to the small size of the fiber interface compared to the casing, the leakage caused by the fiber is negligible compared to the leakage at the casing-cement interface. To obtain more conclusive results, we studied the effects of several parameters. First, the type of cement: we replaced standard Portland G cement with expansive cement to improve the cement’s bonding to the interfaces. We observed that in the presence of optical fibers, the leakage rate in the cement plug increases considerably. Next, we studied the impact of the fibers placement and observed that, despite some variability, placing the fibers in the center is more detrimental to the sealability of the plug than placing them along the casing wall.