Experimental Investigation of Swelling Properties of Kerogen in Contact with Water

Summary Kerogen constitutes a significant volume of organic-rich mudrocks (ORMs) and affects fluid flow in these tight rocks. However, its interaction in contact with formation and injected water is poorly understood, which can pose challenges in the quantification of hydrocarbon production and reserves, water production, and fracturing fluid flowback in ORMs. In this paper, we elucidate the physicochemical mechanisms governing kerogen-water interactions by measuring water adsorption and desorption isotherms using infrared (IR) spectroscopy methods. The results demonstrated that kerogen exhibits sorption-induced swelling behavior. The water adsorption isotherms revealed significant hysteresis and a sharp increase in adsorption at relative humidity (RH) levels above 60%. Water adsorption on kerogen disrupts hydrogen bonds between kerogen molecules, exposing additional binding sites and loosening the structure. This process facilitates the entry of subsequent water molecules, ultimately leading to the formation of water clusters. Swelling of kerogen molecules can potentially have significant impacts on the production strategies deployed in ORMs. For instance, exposure of the rocks to excess water during hydraulic fracturing can cause additional swelling and blockage of flow pathways. It can also potentially explain excessive water production in some ORM formations and can enhance the prediction of water production by honoring the thermal maturity and chemical structure of kerogen.