Abstract
Abstract Barrier materials are essential to avoid uncontrolled migration of fluids in wells. In this paper we review laboratory setups developed over the past decade, focusing on the challenges and the main results. Cement systems based on Portland G cement are still widely used, but new materials are constantly developed to adapt to increasingly demanding field conditions. Laboratory tests provide a cost-effective way to develop and test new barrier materials, specifically for the annulus. Several independent groups have built down-scale setups to study annular barrier materials. Each setup aims to test the barrier material in conditions as close as possible to field conditions. We first describe and compare the different setups, focusing on their features, advantages, limitations and give examples of the results, and compare them with similar setups from the literature. The interactions between a formation, an annular material and the casing opt for many different outcomes regarding sealability. Casing eccentricity or the presence of drilling fluid at the formation wall are some examples of situations where the annular material might exhibit lower performance. However, another important parameter is the ratio between the rock/cement mechanical properties. Large ratios of Unconfined Compressive strength (UCS) and Youngs Modulus leads to higher propensity for creation of flow paths in the annulus. Flow (permeability) testing of these samples illustrate the dynamic behavior of the flow path(s) and how the micro annulus sizes are influenced by the level of the applied confinement pressure around the casing, and by the level of the pressure inside the casing. The evaluation of the flow path geometries using X-ray CT show how complex these geometries appear in "real" systems. This finding further highlights the importance of proper validation/calibration of any flow rate model or calculator. The evaluation also shows that the typical flow paths develop from existing defects. The work presented shows the development of various down-scale setups made with the objective of understanding the behavior of annular barrier materials upon effects such as temperature and pressure cyclic changes. The results illustrate the importance of continuing development of testing facilities to ensure that wells are constructed using optimized barrier materials.