Permeability and Self-Healing Behavior of Alkali Activated Geopolymers for Well Cementing Applications

Abstract

Geopolymers, also identified as alkali-activated materials (AAM), are alternative well-cementing materials with a lower carbon footprint than traditional ordinary Portland cement (OPC). Geopolymers are formed by combining an aluminosilicate precursor, such as fly ash (FA), with an alkaline activator solution. Among their merits is an ability to self-heal after becoming damaged, which can be exploited to restore permeability, sealing ability, zonal isolation, and well integrity in wells that suffer from cracking, fracturing, or debonding in their annular cement sheaths and abandonment plugs.This study investigates the self-healing ability of various alkali-activated Class F fly ash-based geopolymers. Liquid sodium hydroxide (LSH), liquid sodium silicate (LSS), and solid sodium silicate (SSS) were used as activators for the preparation of geopolymer specimens, while Class H OPC was used as the control material. Permeability was characterized using pressure transmission tests (PTT). The tested samples were of different compositions, curing ages (7-day and 28-day), damage stages (pristine, damaged after freeze-thaw cycling, self-healed after post-damage curing), and damage severity (low, medium, and high). Fourier-transform infrared-spectroscopy (FTIR) and loss on ignition (LOI) tests were performed to examine the geopolymer reaction over time, in an attempt to relate the various permeability results to the geopolymerization process. The experimental results show that geopolymers possess low permeability, comparable to – or lower than – OPC, and that effective permeability restoration occurs in geopolymers, even after high degrees of damage. The implication of this work is that geopolymers are promising alternative barrier materials to OPC with a superior ability to guarantee low barrier permeability and appropriate zonal isolation, keys to wellbore integrity over the entire lifecycle of wells, even if those wells suffer from damage.

Keywords: Fly ash (FA), geopolymer, alkali-activators, self-healing, OPC alternative, zonal isolation