An Experimental Investigation of the Impact of Diffusion Osmosis and Chemical Osmosis on the Stability of Shales

Wellbore instability in shales is the most challenging and costly issue in drilling operations. Wellbore instability in shales can be attributed to many factors, some of which have been well studied and documented. However, the physicochemical and mechanical properties alterations in shales that eventually lead to wellbore failure have been largely ignored. Water and ion movements in and out of shales play a major role in the alteration of the physicochemical and mechanical properties of shales, thus leading to wellbore instability problems and possible hole collapse. Water and ions can move in and out of shales by many mechanisms, including, but not limited to, diffusion osmosis, chemical osmosis, convective flow, and capillary suction. This work presents experimental data analyzing the impact of chemical osmosis and diffusion osmosis on water and ion movements when shale interacts with drilling fluids. The adopted experimental work minimized the effect of convective flow and capillary suction. Results show that water movement is not only controlled by chemical osmosis (water activity) as previously thought but is also influenced by diffusion osmosis. This insight provides information and guidelines to optimize drilling fluids to effectively control and mitigate wellbore instability when drilling through troublesome shale.