Are Natural Fractures in Sandstone Reservoir: Water Wet – Mixed Wet – Or Oil Wet?

Abstract

This study accurately measures the wettability contact angle of native Kuwaiti sandstone reservoir that hosts mixed pore size distributions in both the tight sandstone matrix as well as the natural fracture (NF) embedded in it. Also, this study, effectively, investigates the geometrical size and shape of natural available voids whether matrix voids or NF voids captured in the rock 2D image frame system. Correspondingly, this study is, successfully, measure tight matrix, NF Pore wall, and NF pore opening wettability performance and recovery efficiency contributions inside the sandstone reservoir. A model pore/ grain contact angle wettability is generated. Therefore, this study thrives to enhance new physics that will advance reservoir characterization and production improvement through modeled and measured wettability contact angle. The prepared fresh tight sandstone rock sample in the form of rock fragment is imaged and characterized for porosity, permeability, and wettability contact angle in 2D format utilizing SEM-BSE imaging techniques. The generated images will be quantified using pre-defined logic for wettability contact angle measurement. The data generated will be used to estimate the wettability distribution. Each image captured will be investigated for a magnification of X51 (1 mm Scale). This magnification scale will ensure measurement of all possible pore/ grain petrophysical porosity & permeability features, as well as wettability contact angle of 3 region representations for the tight matrix, the natural fracture pore wall, and the inside fracture void. From measured data and computed logics, the majority portions of natural pore voids and pore-walls are medium-water-wet; however, some fracture-pore-walls show mixed and strongly oil wetting preference. The main factors in the understanding the fracture wettability are pore size distribution and pore morphology that suggests the wettability affinity likelihood. This study shows 3 natural pore regions: tight matrix, natural fracture pore wall, and inside the natural void space. These regions are necessary to characterize wettability behavior for oil production and crude oil reservoir recovery schemes, especially in EOR schemes such as water production and/ or water injection operations. Also, the fracture-to-matrix ratio shows some new interesting features characterizations.