Granular Calcium Carbonate Reinforced the Cement Paste Cured by Elevated Temperatures

Area of Science:

• Materials Science
• Petroleum Engineering
• Geochemistry

Background:

• Cement paste in heavy oil thermal recovery wells is exposed to sequential harsh conditions: cyclic elevated temperatures, steam, and high-concentration carbon dioxide (CO2).
• Understanding the impact of these conditions on cement properties is crucial for well integrity and longevity.

Purpose of the Study:

• To investigate the effects of cyclic elevated temperature, elevated temperature, and high-concentration CO2 on cement paste properties and microstructure.
• To analyze changes in compressive strength, pore structure, microstructure, and crystal type under different simulated downhole conditions.

Main Methods:

• Cement paste samples were subjected to cyclic elevated temperature, elevated temperature, and high-concentration CO2 (HCC) conditions.
• Compressive strength tests were performed.
• Low-field nuclear magnetic resonance, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize pore structure, microstructure, and mineralogy.

Main Results:

• Elevated temperature curing degraded cement microstructure, increasing pore size and porosity, reducing compressive strength to 21.04 MPa.
• High-concentration CO2 (HCC) exposure led to the formation of vaterite, aragonite, and calcite within pores and cracks.
• CO2-induced carbonation repaired the cement paste, reducing porosity and increasing compressive strength by up to 169% after 28 days.

Conclusions:

• Elevated temperatures negatively impact cement paste integrity, while high-concentration CO2 acts as a self-healing agent.
• The formation of carbonate minerals (vaterite, aragonite, calcite) during CO2 exposure is key to the observed strength enhancement.
• CO2 sequestration within cement offers a potential mechanism for improving wellbore cement durability in thermal recovery operations.