A Practical Method for Measuring the Liquid Contact Angle of Fracture Proppant Pack

Abstract

Abstract There is lack of a reliable method to determine the liquid contact angle of fracture proppant to characterize its surface wetting property due to the non-flat surface of proppant particle. The objective of this paper is to present and use a new method for determining the liquid contact angle of proppant pack for proppant selection in fracturing oil and gas wells. The water contact angles given by the new method are similar to the contact angles found in literature for the water-air-stainless steel 304 system and the water-air-copper system. The difference is 3%~3.5%, indicating that the new method is valid for determining liquid contact angles on the smooth surfaces of solids. The new method was compared with the sessile drop method for four water-particle pack systems where stable drops were established. The difference in estimated liquid contact angles is between 0.41% and 7.12%, indicating that the new method is valid for determining the liquid contact angles on the rough surfaces of particle packs. The new method was applied to estimating the water and oil contact angles on the surfaces of packs of 11 commercial fracture proppants. Comparison of derived water and oil contact angles suggests that all these proppants are oil-wet proppants. Two proppants are considered more water-wet than other proppants because of their lower water contact angles. Although one proppant was claimed by its manufacturer as oil-wet proppant, its low water contact angle suggests that it is a water-wet proppant. It was observed that liquid contact angle of proppant pack is not sensitive to proppant size for given types of proppants in the range of proppant size tested. The new method requires only drop volume and the wet diameter/area of the proppant pack to derive liquid contact angle. Even a liquid drop sinks into a proppant pack, the contact angle can still be estimated if the wet diameter/area is measurable. The new method may not be accurate in situations where the proppant particle size is so large that the liquid drop sinks into the pore space of the pack without leaving a circular wet area at the pack surface. Further investigations are needed to establish the critical size of the particle size. The liquid contact angles given the new method are dynamic contact angles if the liquid drops are not in thermodynamic equilibrium. The results are good only for comparison of surface-wetting behavior of particles, not for scientific but engineering uses.