To understand the interactions between shale rocks and aqueous drilling fluids, the spontaneous imbibition of water phase into shale pore systemsneeds to be investigated. It is important to study the shale-fluid interactions to mitigate problems associated with drilling shale formations using water-based drilling fluids. Spontaneous imbibition experiments have been frequently conducted to assess the flowback and recovery for reservoir engineering applications. In this paper, the literature has been reviewed in an attempt to link the work that has been carried out in that area to study the water filtrate invasion of drilling fluids into shale rocks while drilling.
Over the years, different techniques and instruments have been used to study the spontaneous imbibition into shale rocks including: spontaneous imbibition device, which is basically analytical balance to measure the weight changes as imbibition progresses, pulse decay permeameter, scanning electron microscopy, X-ray tomography and nuclear magnetic resonance. To aid in analyzing and interpreting the results, the rocks are characterized in terms of: surface area, porosity, permeability and wettability. Fluids that have been used as the imbibing medium included: water, oil, brines, and surfactants.
Three imbibition mechanisms have been revealed by literature: capillarity, osmotic diffusion, and water adsorption. These mechanisms can be distinguished when imbibed water volume is plotted against time where the imbibition rate differs for three distinct regions. Factors that were found to have impact on imbibition process include: capillary pressure, porosity, pore size distribution, pore connectivity, effective permeability, presence of fractures, bedding, mineral composition and clay content, fluid type, and properties and depositional environment (marine or continental).