Grouting of well leakage and migration pathways using colloidal silica: a preliminary experimental investigation

Hydrocarbon well decommissioning and abandonment require the long-term sealing of potential fluid migration pathways. Current grouting technologies based on the use of cementitious grouts may not be able to achieve proper penetration and sealing of migration pathways, this resulting in an environmental risk due to the migration of hydrocarbons or other well fluids out of the well and into the environment.
Colloidal silica (CS) based grouts differ from traditional cement grouts due to their low viscosity (similar to water), and their excellent penetrability governed by the size of the silica nanoparticles (~15nm). As a result, CS grouts have the potential to seal migration pathways (i) at cement/casing or casing/cement interfaces where the cement bond is compromised, and (ii) due to micro-channels and micro-annuli within the cement annulus. This study presents a preliminary laboratory investigation to demonstrate the suitability of CS grout for the purpose of creating multiple barriers within hydrocarbon wells. To this end, CS grout was injected into fractured cement cores using a high pressure/high temperature core-holder apparatus to simulate target downhole scenarios. Microstructural analysis (micro-CT scanning) prior and post treatment were conducted to image the spatial distribution of the grout within the fracture network. The effectiveness of the treatment was measured by evaluating i) the core permeability before and after treatment with CS, and ii) the unconfined compressive strength of treated cement cores.