SWELLING PRESSURE OF MUDSTONE AND ITS RELATIONSHIPS WITH ROCK STRENGTH.

Water and ions in or out of the mudstone have a profound effect on the rock strength, and studying the swelling ability can improve the prediction accuracy of wellbore stability. In this paper, a new equipment has been developed to continuously measure the swelling pressure of the mudstone in different solutions with different ions and different salinities. Moreover, the weight change of mudstone was acquired after the swelling pressure was in a steady state. Furthermore, triaxial compression test was performed to investigate the compressive strength and cohesion of rocks immersed in different water solutions. The results show that the higher the mass concentration of KCl is, the smaller the swelling pressure and the bigger the compressive strength will be. The compressive strength of mudstone contacting with KCl concentration is lower than that of the native mudstone. In addition, it is shown that the compressive strength and cohesion decrease while the swelling pressure increases. The relationship between the swelling pressure and uniaxial compressive strength can be described as an exponential function. Also, the cohesion can be expressed by an exponential function of swelling pressure. [ABSTRACT FROM AUTHOR]