How Shale May Form a Sealing Barrier around a Well

Summary When a well is going to be permanently plugged and abandoned, the annulus between casing and rock has to be sealed at least in certain sections of the well, in order to ensure permanent protection against leakage. In some shale sections it has been found that the rock creeps in and closes the annulus completely, without injection of cement. The process of forming a sealing shale barrier around a well is being studied both experimentally and theoretically. A specific version of the hollow cylinder test, the “Shale Barrier Test”, has been designed in order to investigate the barrier forming process and quality of the resulting barrier. The study shows that the formation of shale barriers can be reproduced in downscaled laboratory tests. This allows for studies of the barrier forming process and the efficiency of the resulting seal.