Microcapsule Transport in Transparent Rough Fractures for EGS Fracture Modification

Abstract

Polymer-based injectates delivered by microcapsules are being evaluated as a means to modify fracture permeability to limit preferential flow that can lead to thermal short-circuiting. The microcapsules are sized so they enter only the larger, problematic fractures and rupture at elevated temperatures anticipated in the reservoir to deliver the polymer at the desired location. We report on experiments to understand microcapsule transport and determine the fracture size below which microcapsules are excluded from entry, i.e., the blocking function, for a rough fracture. Flow visualization experiments were conducted to study the flow of microcapsules using water as the carrier fluid in transparent, horizontal rough fractures. The fracture characteristics (aperture, connectivity) was varied by both normal and shear displacement. A camera was used to record movement of the particles in the fractures. Microcapsule passage through, retention in, and exclusion from the fracture were measured. Image analysis methods were used to track microcapsule movement and interpret the amount of fracture blocking that occurs as a function of fracture characteristics and microcapsule size.