Because of their distinct characteristics, such as mineralogical and microstructural heterogeneity, complex pore structures, and nano-scale pores, making use of high-resolution images has been a developing trend to understand shale microstructure and fluid flow at the desired scale. In this study, we use focused on ion beam-scanning electron microscope (FIB-SEM) image stack obtained from Eagle Ford formation to model two-phase fluid flow and evaluate the impact of connectivity loss on relative permeability curves. Three-dimensional (3D) pore structure constructed from two-dimensional (2D) image is first analyzed for static petrophysical characteristics, with further fluid flow modeled using the Lattice Boltzmann Method (LBM) to determine single phase permeability as well as two-phase relative permeability curves. Finally, the pore connectivity is quantified based on Euler-Poincare Characteristics (EPC) as a function of sample size and further analyzed for correlation with calculated parameters. Results show that the total porosity of the studied sample is around 12.5 % which reduces slightly with increasing sample size. In contrast, the connected porosity decreases by more than 50% when the sample size is around 6 μm. Moreover, single phase permeability calculated from LBM simulations is around 1.17 μd for the whole sample and the calculated permeability values are decreasing significantly with increasing sample size; i.e. 15000 times reduction is observed when the sample size is at 6 μm. Furthermore, results indicate that relative permeability curves are also a strong function of pore connectivity as well as sample size, whereas residual saturation is mostly a function of pore body to throat ratio and impact of pore connectivity is minimal. More interestingly if the images are analyzed in backward sequences then increase in porosity, connected porosity, and permeability is observed. The results from this study will provide new insights for learning about nano-scale pore structure characteristics and improve reservoir simulation of shale reservoir.

Impact of pore connectivity on two-phase relative permeability in shale formations

2019 Spring National Meeting

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