The use of a new ultra low density admixture has been developed which, when used in blends of Portland, Pozzalanic and Gypsumcements, produces cementing slurries with properties of low density and high compressive strength. This material also results in cements having unusually low levels of thermal conductivity.
This paper discusses the results of two years of application in the Canadian oilwell cementing industry. Descriptions of various applications of the material aregiven. These include offshore applications, applications in severe lost circulation areas requiring very low thermal conductivity, and its use in cementing large diameter low collapse strength fibreglass casing in an unusual experimental thermal recovery project in one of the heavy oil areas.
The problem of accurately measuring the water to cement ratio in a slurry where the slurry density approaches water is considered.
In 1979, HSMS admixture (High Strength Micro-Spheres), was introduced to the Canadian oilwell cementing industry. The material, consisting of hollow ceramicspheres, offered new thresholds in the design of light weight cement slurries.
The light weight and pressure resistant nature of HSMS has allowed the exploitation of the material for several difficult applications. The first is cementing through or above weak zones which are subject to breakdown and lost circulation. This advantage of low hydrostatic pressure has been utilized in cementing offshore wells in the Sable Island area, and also in the area east of St. John's, Newfoundland. Applications requiring low hydrostatic pressures in Alberta have been through the Woodbena, Beaverhill Lake, and Slave Point formations in the Peace River area of northwestern Alberta, as well as in cementing the shallow lower Cretaceous Sands of eastern Alberta and western Saskatchewan. Projects along the Alberta-Saskatchewan border have largely been associated with thermal recovery schemes. Various blends of Class G cement. HSMS and silica flour for high temperature strength stability have been used. Fig. 1 shows the locations in western Canada where major use has been made of HSMS.
HSMS are hollow, thermally fused spheres. Because they are hollow, the admixture is subject to a progressive change in effective density as the pressure resistance of individual spheres is exceeded. Table 1 presents their effective density and absolute volume QS it function of pressure.
Particle size distribution is presented in Table 2. It will be noted that 89.5% of the spheres are in the 62 – 250 µm range.
The low specific gravity of HSMS, when combined with portland cement and other additives. produce cement slurries as light as 960 kg/m3.
Much lab work has been done to test the compressive strengths of HSMS blends. While the possible blends are nearly infinite in number, it is informative to compare compressive strengths of HSMS cements with conventional cements within the common density range of the two types.
Table 3 presents comparative compressive strength data for several different blends. It can be seen that within a given density range, HSMS provides 24 hour compressive strengths ranging from 1503 to 4001.
