Modeling of the Correlation Between Mineral Size and Shale Pore Structure at Meso- and Macroscales

Inorganic pore structures are critical to understand the oil and gas transport and storage properties of unconventional reservoirs. However, it can be difficult to quantitatively and qualitatively interpret the relationship between the inorganic pore structure and particle arrangement in terms of particle size and the brittle and clay mineral composition of shale. In this paper, artificial core simulations and mathematical modeling were performed to explore the effects of brittle mineral and clay mineral assemblages on shale pore structures. The artificial cores were subjected to computerized tomography and scanning electron microscopy analysis, as well as porosity and permeability testing. The results show that shale porosity and permeability increase with the brittle to clay mineral particle size ratio. This phenomenon is caused by the different arrangements of inorganic minerals in shale when the brittle to clay mineral particle size ratio is < 1 and > 1. A theoretical mathematical model based on mineral arrangement shows that shale permeability can be characterized by the inverse proportional function of mineral particle size. This investigation of shale pore heterogeneities on meso- and macroscales based on artificial cores provides new insights into the simulation of oil and gas transport in micro- to nanoscale pores and the understanding of pore evolution during the first diagenesis stage of shale, which is mainly composed of inorganic minerals.