Experimental Inspection of the Influence of Chemical Osmosis on Shale Swelling and Subsequent Wellbore Stability

Abstract

Linear swelling and gravimetric ions and water uptake tests were experimentally conducted to examine the effectiveness of osmotically extracting water out of shale in the presence of dilute and concentrated salt solutions. In addition, vast data on shale’s membrane efficiency were collected from the literature to aid in this work. The main findings of this study confirmed that water transported into shale by diffusion osmosis may negate the benefits of water extraction out of shale by chemical osmosis. This is in line with previously reported results which suggested that shale acts as a nonideal leaky semipermeable membrane which allows ions to pass through. In addition, it was shown that shale swelling could occur due to diffusion osmosis and may dominate the swelling behavior of shale when it interacts with concentrated solutions. It was also shown that ion type and concentration could affect the amount of swelling that may be experienced by shale when exposed to salt solutions. Data from this work recommends incorporating dilute salt solutions in the make-up of drilling fluids to ensure that water extraction out of shale by chemical osmosis overtakes water flow into shale by diffusion osmosis. In addition, a critical salt concentration must be determined above which diffusion osmosis becomes dominant. The findings of this study can help us better understand the interaction between shale and drilling fluids and to improve drilling fluids design.