Research on surface modified vitrified microbeads for enhanced geothermal insulation cement

Abstract:

Using thermal insulation cement in the upper non reservoir section of geothermal extraction wells will be beneficial for increasing outlet temperature and improving energy utilization efficiency. Vitrified microbeads have been widely used in building exterior wall insulation due to their advantages of light weight， low cost and low thermal conductivity. However， due to its poor adhesion between the passivated surface and the cement matrix， the strength of the composite cement decreases linearly with the increase of its dosage. This article uses methods such as acid corrosion， high-temperature burning and spraying silane coupling agents to carry out surface modification of vitrified microspheres， and uses the modified vitrified microspheres to prepare geothermal insulation cementing cement. The surface morphology of vitrified microspheres before and after modification was characterized， the effects of modified and unmodified microspheres on the strength， hydration products， and interface morphology between microspheres and cement matrix were studied by micro testing methods such as SEM， XRD， etc. The following conclusion can be drawn： for microspheres with lower density， when mixed with cement of equal mass， the cement matrix does not cover the surface of the microspheres enough， resulting in a rapid decrease in the strength of the cement stone after its addition； After curing at 60 ℃， the compressive strength of the modified vitrified microsphere cement increased by 173.5%， and the addition of magnesium fluorosilicate further enhanced the strength； After modification， the increase in surface roughness of microbeads promotes the adhesion of hydration products， enhances the activity of microbeads involved in the overall hardening process of cement， and improves the bonding between cement matrix and microbead surface， collectively improving the strength of cement stone.

Key words:geothermal extraction well;wellhead temperature;vitrified microbeads;silane coupling agent;surface modification