Effects of the laminated-structure and mixed wettability on the oil/water relative permeabilities and oil productions in shale oil formations

Abstract

Shale oil formations are highly heterogeneous laminated systems containing organic matter (OM). In this study, oil/water flow in laminated shale oil formations are investigated from the pore-scale perspective using the lattice Boltzmann method (LBM). The effects of the pore size and wettability heterogeneities including different pore sizes, contents of OM, wettabilities of OM, and OM distributions on oil/water flow are analyzed. The relative permeability curves of water and oil are calculated and then substituted into the model of numerical simulations to analyze the variations of oil production for each case. Results showed that the relative permeabilities of the mudstone and sandstone laminae are different, and that using the average relative permeabilities of the two laminae can lead to significant errors in the calculation of oil production. With the content and the hydrophobicity of OM increasing and with OM locating in the middle of the mudstone, more oil occupies the pore space around OM and thereby increases the relative permeability of oil (kro) in the mudstone, but conversely decreases kro in the sandstone, which in turn affects the proportions of oil production through the mudstone and sandstone.