Advanced High-Temperature Lightweight Foamed Cements for Geothermal Well Completions

Abstract

Foamed cement slurries that were prepared by mixing a cementitious material having a Class H cement to silica flour ratio of 1.0 in conjunction with a alpha olefin sulfate foam surfactant and a coconut diethanolamide foam stabilizer were exposed in an autoclave at a temperature of 300°C and a hydrostatic pressure of 2,000 psi (13.79 MPa). One lightweight slurry having a density of 9.61 lb/gal (1.15 g/cc) yielded a cellular cement having a compressive strength at 24 hr of >1,000 psi (6.9 MPa) and a water permeability of 10/-3 darcys. The factors responsible for the attainment of these mechanical and physical properties were identified to be well crystallized truscottitie phases and a uniform distribution of discrete fine bubbles. The addition of graphite fiber reinforcement for the cement matrix significantly suppressed any segregation of foam caused by thermal expansion of the air bubbles and further improved the mechanical characteristics of the cured cements.