Abstract
Understanding the distribution of water in organic-rich shales is crucial to quantifying the relationship between oil well productivity and recovery of fracture water, to evaluating or interpreting multiphase flow measurements and simulations for wettability and relative permeability effects and to accurately model storage of hydrocarbons. There exists a widely held view that organic pores are generally hydrocarbon-wetting, while the inorganic porosity is water-wet and forms the primary locations for the trapping and storage of water. Although there is good evidence for this model, recent experimental work indicates that water can potentially be trapped in organic pores as well thereby impacting hydrocarbon reservoir performance. The study of the governing factors controlling the distribution of water in organic rich shales is therefore merited.
This manuscript focuses on a pore-scale study of the distribution of water in organic kerogen shale nanopores. It examines the sensitivity to pore size, degree of kerogen maturity and pore wall roughness on the storage of water. Additionally, the effects of pore filling and phase changes in kerogen nanopores that are a result of the characteristics of nanopore confinement of water are demonstrated. Lastly, we also observe some characteristics of multilayer adsorption.
This study employs organic pore models that bear structural resemblances to well-known kerogen molecular structures in terms of some key properties including surface roughness, complex internal porosity, and material disorder. The role of the degree of maturity of kerogen is modeled by varying the abundance of oxygenated functional groups within the model. The results for different pore sizes are compared to the traditional graphite slit pore model that has previously been adopted as a proxy for kerogen pores to highlight the impact of kerogen maturity and surface roughness on the distribution of water.
