Mechanisms of water adsorption into partially saturated fractured shales: An experimental study H. Roshan a,⇑ , S. Ehsani b , C.E. Marjo c , M.S. Andersen a , R.I. Acworth a a Connected Waters Initiative Research Centre, School of Civil and Environmental Engineering, University of New South Wales, 110 King St, Manly Vale, NSW 2093, Australia b QGC-BG Group Company, Brisbane, Australia c Mark Wainwright Analytical Centre, University of New South Wales, Sydney, Australia highlights  Fracture permeability of shales varies with salinity.  Chemically induced micro-fractures are less likely to occur at subsurface condition.  Contact angle of shale-solution system is highly salinity-dependent.  Hydration processes dictate flow direction in unsaturated shales. article info Article history: Received 23 August 2014 Received in revised form 3 July 2015 Accepted 6 July 2015 Available online 10 July 2015 Keywords: Fractured shales Hydraulic fracturing fluid Hydration/dehydration Partially saturated shales Organic-rich shale abstract The physico-chemical processes of water adsorption into water saturated shale rocks have been extensively studied in the past. However, the physico-chemical processes of water uptake into partially saturated shales, such as water loss to fractured organic-rich shales during hydraulic fracturing, are poorly understood which in turn has raised serious technical and environmental concerns. Therefore, we ran a series of experiments on partially saturated calcareous shale samples, with measured total organic carbon (TOC) of 1.935% and mean vitrinite reflectance (Ro) of 0.52%, to identify the potential mechanisms involved in the water uptake. The physico-chemical properties such as mineral and elemental compositions, initial water saturation and contact angles of solutions with different concentra- tions were measured. Free and confined adsorption tests were then performed on both the intact and artificially fractured shale samples. The experimental results of this study are explained by two proposed mechanisms; capillary hydration and surface–osmotic hydrations that can combine to influence the amount of water uptake into partially saturated shales. The results show that the crack initiation is a strong function of confining stress and cracks are formed parallel to weak structures of the rock (bedding planes and laminations). The results also reveal that the mineral hydration controls the permeability (and consequently water flow) of existing fractures within the shale sample. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Shales are finely laminated rocks with properties that are char- acterised by their mineral components and structure, cation exchange capacity, specific surface area and water saturation. These rocks, potentially containing hydrocarbon resources, have long been the focus of environmental and energy studies. For instance, shale formations have been suggested as good candidates for nuclear waste disposal [1] where the environmental concern of waste leakage has demanded an extensive study of shale thermo- dynamic behaviour in recent years. Furthermore, shales are often encountered during drilling operations and cause severe borehole stability issues [2] and as a result, research has been continually carried out to characterise the properties of shale rocks. However, previous studies have been mainly focused on water sat- urated inorganic shales [3] or partially saturated unconsolidated clays [4]. The ever increasing world demand for energy has inspired the development of unconventional deep shale gas and oil reservoirs http://dx.doi.org/10.1016/j.fuel.2015.07.015 0016-2361/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: h.roshan@unsw.edu.au (H. Roshan). Fuel 159 (2015) 628–637 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel