A review of shale swelling by water adsorption

Due to the improvement of drilling and recovery techniques, shale gas exploration has developed rapidly over the past ten years, and problems that have arisen have attracted increasing attention. Swelling of shale with the adsorption of water is one of the leading problems for shale gas exploration, as it causes wellbore instability and shale formation collapse. The main objective of this study is to investigate the relationship of factors that influence shale swelling. On the basis of previous studies, three factors - initial water content, clay fraction and confined pressure - were selected for analysis. In order to further understand the speed of shale swelling, investigations of specimens with different initial water/moisture contents swelling in water/humid conditions are summarized. The results show that water adsorption creates higher swelling volume than moisture adsorption and the maximum swelling speed occurs at an initial water content of about 14%. To measure swelling potential, a multiple linear regression model is developed to obtain an equation to predict shale's swelling potential. According to the regression results, shale swelling is negatively linearly related to initial water content and logarithmic confined pressure, and is correlated linearly with clay fraction.