Research On Ultra Light Weight Hollow Glass Microspheres Cement For High Temperature Geothermal Wells

The temperature of geothermal wells is usually higher than the conventional oiland gas wells. High temperature will cause reduction in compressive strength knownas strength retrogression and shorten its thickening time in cementing job. The secondmajor challenge is lost circulation caused by highly permeable reservoirs, lostcirculation is a very serious problem, because of the expense associated with thecement lost into the formation. In some serious region of lost circulation, it can notmeet technical requirements by using normal light weight cement. In addition,underbalanced drilling technology was utilized in some special formation, ultra lightweight cement was also used in cementing job, some formations need to usethe cement which has a slurry density as low as1.0g/cm3.The most common method of creating light weight cement designs in thegeothermal industry is the use of high-strength microspheres (HSM). This paperintroduce the design difficulties of the microsphere ultra light weight cement for hightemperature geothermal wells. Based on a detailed survey of literature, class G oilwell cement and silica flour were used as the basic cement.Secondly, we analysiscommon light weight materials including bentonite, fly ash, microsilica, floating bead,gas and hollow glass microspheres and corresponding cement in order to knowtheir properties and application. At last, we choose a domestic high performancehollow glass microspheres T46as the light weight material of ultra light weightcement for high temperature geothermal wells. Hollow glass microspheres show highpressure resisting capability and show obviously effect that density can be reduced to1.10g/cm3. The system was in an unstable state owning to abundant lighteningmaterial, so microsilica with fine particle size was added to the system,which can befurther filled cement paste pore, forming a more dense cement paste, significantlyincreased the strength and stability of the slurry.The design of ratio between microsilica and hollow glass microsphere is byemploying the Andersen particle packing model. Water cement ratio is confirmed bytesting water requirement of hollow glass microspheres and microsilica, forming a system of ultra light weight cement which has a density varies form1.0g/cm3to1.4g/cm3. The slurry density, thickening time, API fluid loss, free fluid and compressivestrength of the designed cement are measured and analyzed. Phase identification anddevelopment of microstructure were studied by X-ray diffraction and scanningelectron microscope.The results show that the ultra light weight hollow glass microspheres cementrevealed some good properties, such as a higher compressive strength and lower APIfluid loss. Additionally, results from phase identification and development ofmicrostructure shows that hydrothermal reaction products includes quartz, hydratedcalcium silicate and tobermorite phases, this makes the system has an excellentcomprehensive properties.