Effect of Fluid Contact Angle of Oil-Wet Fracture Proppant on the Competing Water/Oil Flow in Sandstone-Proppant Systems

Abstract

Ceramic fracture proppants are extensively used for enhancing the recovery of fossil energy and geothermal energy. Previous work has reported the attracting-oil-repelling-water (AORW) property of oil-wet proppants at the faces of fractures. Because of the lack of a method for measuring the contact angle of proppant packs, the terms water-wet proppant and oil-wet proppant were defined based on observations of liquid droplets on the surfaces of proppant packs without quantitative measurement. An innovative method was developed in this study to determine the contact angles of fracture proppant packs. The effect of the oil contact angle of the oil-wet fracture proppant pack on the competing water/oil flow from sandstone cores to the packs was investigated. It was found that, for a given fracture proppant pack, the sum of the water contact angle and oil contact angle measured in the liquid–air–solid systems is less than 180°, i.e., the two angles are not supplementary. This is believed to be due to the weak wetting capacity of air to the solid surfaces in the liquid–air–solid systems. Both water and oil contact angles should be considered in the classification of wettability of proppant packs. Fracture proppant packs with water contact angles greater than 90° and oil contact angles significantly less than 90° can be considered as oil-wet proppants. Reducing oil contact angles of oil-wet proppants can increase capillary force, promote oil imbibition into the proppant packs, and thus improve the AORW performance of proppants. Fracture proppant packs with water contact angles less than 90° and oil contact angles less than 90° may be considered as mixed-wet proppants. Their AORW performance should be tested in laboratories before they are considered for well fracturing operations.