Mathematical simulation of clay swelling due to water imbibition

Clay minerals are commonly encountered in the drilling for oil and natural gas and have the potential to expand considerably when they come into contact with drilling fluids. Clay swelling is a significant issue in the drilling industry, leading to a number of borehole stability problems. This thesis develops a mathematical hydromechanical model to simulate the deformation due to swelling during capillary suction of water in unsaturated clays. The model builds on an existing framework associated with coal shrinkage during coalbed methane extraction. Sorption of water in the model is represented by a Langmuir isotherm and a swelling strain term has been derived by adapting the theory of linear poroelasticity. The results show that for a clay plug with a low initial effective saturation (Se0=0.001) the amount of swelling correlates with clay content. These modelled results were compared with experimental swelling curves for two pure clay plugs and showed that, although the final swelling points converged, the swelling curves evolved at different rates. These findings indicate that further research is required before this model can be used to simulate clay swelling with a high degree of accuracy.