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

Abstract

This study accurately measures the wettability contact angle of native sandstone reservoir that hosts varied pore size distribution in both sandstone matrix and a natural fracture. Also, successfully, investigates the size and shape of natural various available of pores in the rock and their wettability performance and recovery efficiency contributions inside the sandstone reservoir. A model pore/ grain contact angle wettability is yielded, and this study thrives to understand their new physics that will advance reservoir characterization and production improvement.

The prepared tight sandstone rock samples in the form of rock fragment will be imaged and characterized for porosity, permeability, and permeability 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 to ensure all possible features wettability size and number representations for the matrix as well as the natural fracture to matrix relationships.

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 likely affinity. This study shows 3 natural pore regions: tight matrix, natural fracture pore wall, and inside the natural void space. These regions are necessary to be wettability characterized for oil production and crude oil reservoir recovery schemes, especially in EOR or water production and water injection operations. Also, the fracture-to-matrix ratio also shows some new interesting features characterizations.