An experimental study of the swelling behaviour of mudrocks in the presence of water-based mud systems

Swelling behaviour of three different mudrocks (London Clay, Oxford Clay and Fuller's Earth) of varying composition, geological ages, degree of lithification, organic matter and expandable clay contents have been investigated in the presence of water-based mud systems (KCl/CMC, Polyamine, Polyamine + glycol and PHPA + glycol) plus water to identify the factors controlling the swelling behaviour of shales. The results show that the degree of swelling is not directly correlatable with the proportion of swelling clay minerals in the mudrocks. Based on the experimental results, the swelling behaviour of the mudrocks depends on the composition, geological history and degree of lithification of the mudrocks. Well lithified smectite-rich mudrock was found to show less swelling than less well lithified mudrocks with lesser amounts of swelling clays. Organic matter rich mudrock showed a greater degree of swelling than those with little organic matter, suggesting that organic matter may also influence the swelling behaviour. This investigation provides a better understanding of the swelling behaviour of mudrocks by introducing the concept of the combined action of physico-chemical and mechanical swelling processes.