BEHAVIOR OF WATER IN NANOPOROUS REGIMES RELEVANT TO SHALE

Complexity in fluid-mineral systems takes many forms including the interaction of dissolved constituents in water, wetting of surfaces, adsorption of dissolved and volatile species, the initiation of reactions, and transport of mobile species into and out of the rock matrix. Indeed, despite the extensive length and time scales over which fluid-mineral interactions can occur, there is the inescapable fact that interfacial phenomena – i.e., mineral surfaces (hydrophobic versus hydrophilic) as well as buried interfaces such as pores, pore throats, grain boundaries, microfractures and dislocations at the atomic scale – control the exchange of matter and impact the nature of multiphase flow and reactive transport in geologic systems. The overall objective of our work is to interrogate the interfacial behavior of fluids restricted to nanoporous regimes or interacting with 2-D solid surfaces relevant to tight formations such as shale. Our study focused on the behavior of water adsorption at elevated temperatures for a variety of engineered proxies and natural nano-porous matrices that compose a significant fraction of a shale. The objectives are three-fold. First, we describe a novel experimental adsorption apparatus capable of interrogating water sorption behavior to 200^oC; second, we explore water adsorption/desorption behavior of several classes of porous materials relevant to shale at temperatures of 105, 150 and 200^oC; and third, we provide examples of how molecular dynamics simulations help describe the structure and dynamics of water under nanoconfenment. Analysis of adsorption results in this range of temperatures is expected to allow for differentiation between key adsorption mechanisms (e.g. capillary condensation vs. multi-layer adsorption) and insights into the ‘hysteresis phase diagram’ for the confined fluid. These results may contribute to our understanding of how hydraulic fracturing fluid (mostly H₂O) imbibe in shale and why recovery of gas and flowback water can beo limited in many formations (e.g., Utica/Pt. Pleasant) that are initially very under saturated with indigenous water.