An Experimental Investigation on the Impact of Diffusion Osmosis, Chemical Osmosis, and Capillary Suction on Shale Alteration

摘要

Well bore instability in shales can be the most challenging and costly issue in drilling operations. Well bore instability in shales can be attributed to many factors, some of which have been well studied and documented. However, the physicochemical and mechanical property alterations in shales, which eventually lead to well bore failure, have been largely ignored. The movement of water and ions in and out of shales plays a major role in the alteration of the physicochemical and mechanical properties of shales. Water and ions can move in and out of shales by many mechanisms. The mostly agreed on mechanisms that are responsible for water and ion movement in and out of shales are diffusion osmosis, chemical osmosis, convection (e.g., hydraulic flow), and capillary suction. This article presents experiments used to analyze the effects of chemical osmosis, diffusive osmosis, and capillary suction on water and ion movement when shale interacts with drilling fluids. Results show that water movement is not only controlled by chemical osmosis (water activity), but is also influenced by diffusive osmosis and capillary suction. The immersion of shale into fluids changes the chemical composition of the shale due to ion movement, and thus its physicochemical and mechanical properties are altered. The gravimetric-swelling test is used in the laboratory to acquire a better understanding of the relationship between water flow, ion flow, and shale swelling. Insights gained from this study provide information used to optimize drilling fluids to effectively control or mitigate well bore instability when drilling through shale.