CO₂ geological storage: Microstructure and mechanical behavior of cement modified with a biopolymer after carbonation

¹ Engineering Faculty, Universidad Nacional de la Patagonia San Juan Bosco, 9004 Comodoro Rivadavia, Chubut, Argentina.
² Navier, Ecole des Ponts, Univ Gustave Eiffel, CNRS, Marne-la-Vallée, France.
³ E.T.S.I. Caminos, Universidad Politécnica de Madrid, Prof. Aranguren 3, 28040 Madrid, Spain.

^* Corresponding author: d.manzanal@upm.es

Abstract

Large amounts of CO₂ could be stored underground in deep rock reservoirs and could help reducing emissions into the environment. Carbon geo-storage technologies have several years in development and new techniques and materials are being studied to make this procedure more effective and less expensive. The risk of leakage from geological reservoirs to other rock formations or even towards the surface means that long-term behavior must be carefully studied. The carbonation of the cement used for sealing the wellbore may compromise the borehole integrity. In light of this problem, this work aims to analyze the poromechanical behavior of cement with and without a new additive in a CO₂ environment. Bacterial nanocellulose is a biopolymer that modifies important cement properties such as compressive strength, thermal behavior and hydration degree. Two cement types were studied: class G cement and modified class G cement with bacterial nanocellulose. These samples were submitted to a supercritical CO₂ environment (temperatures higher than 32 °C and pressures higher than 8 MPa) during 30 days. Mercury intrusion porosimetry and uniaxial compressive strength tests were performed on these samples to study the effect of carbonation. Both types of cement are affected after carbonation by reducing compressive strength and Young’s modulus (E), however, the strength of modified cement was reduced by 8%, while non-modified cement was reduced by 20%.