Application of Young-Laplace with size-dependent contact angle and interfacial tension in shale

Abstract

Shale has been studied extensively since its hydrocarbon recovery became economical, but there are still uncertainties in the applicability of existing models for characterizing its transport properties. A relevant example is the Young-Laplace equation (YL) for interpreting capillary pressure measurements. This study implements its contact angle and interfacial tension as functions of pore throat size to extend its applicability to shale. This study shows a threshold throat size below which implementing size-dependent (actual) properties is crucial. The threshold size is close to 10 nm. The error of the common approach (fixed contact angle and interfacial tension) increases from 5% to 20% where the throat size decreases from 10 nm to 2 nm.This study applies the actual properties to determine the pore throat size distributions of two shale samples. Implementing actual properties influenced the common interpretations from 20% to 50% of the pore volumes of the samples. This study also quantifies the error of the common approach in calculating the pore-throat size. More importantly, it proposes a simple relation that provides a convenient tool for modifying the existing data to determine the actual pore throat size. The results and the simple relation have applications in characterizing the transport properties of shale formations.