Water Sorption and Distribution Characteristics in Clay and Shale: Effect of Surface Force

Abstract

Characteristics of sorption and distribution of water in nanoporous shale are topics of great interest to evaluate unconventional reservoirs. Also, a study of surface force of water/solid interaction at nanoscale is significant for understanding the storage of initial water and the fate of residual treatment liquid in shale systems. In this work, the thickness and stability of water film were investigated by vapor sorption experiments on clay and shale samples. Meanwhile, an approach based on surface forces (disjoining pressure), which resulted in the instability of adsorbed film transition into condensed bulk liquid, was developed to describe molecule/pore wall interactions. Our experimental results directly demonstrated the occurrence of capillary condensation in hydrophilic clay minerals; however, water would not entirely fill in shale nanopores even under high-moisture conditions. This remarkable finding is mainly due to the inaccessibility of water molecules to micropores of hydrophobic organic matter. In addition, the water distribution characteristics are also significantly influenced by pore scale. Under a moist condition with certain relative humidity (e.g., RH = 0.98), the water distributed in hydrophilic inorganic pores with different sizes was mainly classified as (i) capillary water in small pores (e.g., <6–7 nm) and (ii) water film in large pores (e.g., >6–7 nm). In contrast, the surface repulsion prevents water condensing and likely results in a monolayer water film sorption in hydrophobic organic pores (e.g., θ = 100°). Therefore, in an actual shale system with initial moisture content, the inorganic microporosity totally blocked by water might be incapable of gas transport or storage, while the hydrophobic organic pores mainly provide effective space for gas accumulation.

Investigation of the controlling rock petrophysical factors on water phase trapping damage in tight gas reservoirs

“…High irreducible water saturation can generally be associated with the smaller pore throat radius after drainage . The size of larger pore channels is reduced due to the water film while some smaller pore channels are totally occupied by water .…”

“…High irreducible water saturation can generally be associated with the smaller pore throat radius after drainage. 39 The size of larger pore channels is reduced due to the water film while some smaller pore channels are totally occupied by water. 40 The effect of water film on effective pore throat channel size can be described using the formula r e = r − h, where r e is the gas flow pore throat channel and h is water film thickness.…”

Wetting Behavior of Tight Rocks: From Core Scale to Pore Scale

“…The effect of surface forces (acting between two interfaces) on the stability of the liquid film coating the solid surface becomes more important when the size of pore‐throat decreases to less than 100 nm (Chaturvedi et al, ; J. Li et al, ). In unconventional resources (e.g., tight oil formations and shales), the wettability evaluation becomes more challenging (Binazadeh et al, ; Roshan et al, ; H. Singh, ) since (i) a significant portion of pores has the throat radius less than 1 μm and (ii) there exists a wide spectrum of components with different wetting affinities such as organic matter and clays.…”

“…The effect of surface forces (acting between two interfaces) on the stability of the liquid film coating the solid surface becomes more important when the size of pore-throat decreases to less than 100 nm (Chaturvedi et al, 2009;J. Li et al, 2016).…”

Ion Diffusion Behavior between Fracturing Water and Shale and Its Potential Influence on Production

“…In view of the performance of shale hydraulic fracturing methods, a large amount of fracturing fluid (generally more than 30%) is retained in shale formations after flow back [3]. The interaction between water and shale plays an important role in large-scale hydraulic fracturing [4][5][6]. Water has an enormous influence on the mechanical behaviors [7], effective flow channels [8], flow-back methods [9], and gas production patterns [10] of unconventional reservoirs.…”