Methodology for obtaining contact angles in rock sample images using image processing and polynomial fitting techniques

Abstract

Abstract Estimating the contact angle in very complex rock pores presents some challenges to accurately identify the fluid–rock contact surface. This work presents a methodology to estimate the contact angle formed by the brine–rock and the brine–oil interfaces on processing high-resolution images provided by micro-CT scan. We focus the discussion on the limitations of the most popular computational techniques used to determine the contact angle and discuss how to select a practical way to evaluate it. The method consists of four steps: (1) processing the images to determine each fluid present in the image, (2) selection of the pixels that will be part of the contact interface of fluids and the contact point, (3) fitting polynomial equations for each interface and selection of the equation that gives the lowest error, (4) estimation of the contact angle based on the more appropriate polynomial equation. The contact angle is calculated based on the slope of the interfaces’ tangents at the contact point. Several types of approaches were tested to determine the contact interface and the contact point. In order to evaluate the applicability of our method, we use an analytically generated image and rock sample images. Potential errors between the angle obtained from the analytically generated image and the angle calculated from the method show the impact of the right selection of pixels during the image processing step. High sensitivity is also observed for the tangent values in the presence or absence of pixels from the rock sample analysis.

Keywords

• Contact angle
• Image processing
• Oil recovery