Flow patterns of a resin repair material in a vertical wellbore microannulus

Abstract

We studied the repair of a simulated wellbore microannulus between cement and steel using a resin repair material. The experimental configuration consisted of a rough cement surface and a transparent acrylic plate on top of it to serve as a surrogate for steel as it has similar wetting characteristics for the fluids of interest in this study. The microannulus was repaired in a vertical configuration, so the buoyant, capillary, hydrostatic and viscous forces affected the repair. The interaction among those forces determined the flow patterns that developed as the resin was injected into the microannulus and the efficiency of the repair. The microannulus was first saturated with water, and then resin repair material without hardener was injected at the bottom of the microannulus until it arrived at the top of the microannulus (“breakthrough”). The injection of the repair material was conditionally stable since the resin was less dense than water, but more viscous. If the injection velocity was great enough, the resin would effectively displace the water; if not, buoyant forces dominate, and flow became unstable. In addition, the aperture distribution of the microannulus added the complexity of varying capillary forces. The experiments revealed a wide range of behaviors as a function of injection velocity, from pulse flow with apparent saturation of resin at breakthrough of only 4.4% at low velocities to a much more compact displacement at higher velocities, achieving a 67.8% apparent saturation at breakthrough.