Use of Hollow Glass Spheres in Lightweight Cements - Selection Criteria

摘要

Cementing across highly depleted zones and weaker formations requires low density cement systems capable of reducing the hydrostatic pressure of the fluid column during cement placement. If wellbores encounter weak or depleted zones, standard cement cannot be used because the bottom-hole pressure will exceed the pressure gradient and cement will be lost to the formation. Service companies offer cement solutions made light enough to circulate in such situations while retaining the ability to withstand down- hole conditions and maintaining adequate compressive strength to meet regulatory guidelines. Lightweight cements can be achieved using water extension, foamed cement or lightweight microspheres. This paper focuses on the use of lightweight microspheres as density reducing agents. Preliminary experimental data comparing different grades of hollow microspheres is discussed. Cement slurries containing hollow glass spheres and other lightweight hollow microspheres were evaluated while still liquid and after cured. While still liquid the cement slurries were characterized in terms of effective density as a function of pressure. After being cured at room conditions, the resulting cement specimens were characterized in terms of compressive strength. Experimental data suggests that cement compressive strength is mostly independent of the lightweight microsphere strength and strongly dependent on the cement load. Guidelines on the selection of the appropriate microsphere grade are also presented.