Abstract
When designing the cement slurry for casing string cementing in geothermal boreholes, the appropriate thermal conductivity is selected. In the zone of geothermal water, where thermal energy is collected, cement slurry is used, from which the cement sheath has high thermal conductivity. On the other hand, the remaining part of the opening is sealed with slurry, from which the cement sheath will reduce thermal energy losses through appropriate thermal insulation. Cement slurry with appropriate thermal insulation includes light insulating materials. However, the use of such additives is very problematic as they are fractionated due to their low density. Therefore, measures should be taken to prevent fractionation of the cement slurry for sealing geothermal boreholes. This article presents the results of research on fractionation of cement slurries for sealing geothermal boreholes. 12 slurries were used for the tests. Six of them are based on class A cement, and six based on class G cement. This action shows the differences in fractionation depending on the binder used. However, the main area of research is determining the effectiveness of counteracting fractionation by the means used for this purpose. As a result of the conducted works, a very good improvement of the cement slurry stability is obtained after the introduction of xanthan gum, as well as filtration perlite. These measures prevent fractionation, so that the cement slurry has a homogeneous structure, and the cement sheath provides the required thermal insulation in the geothermal well.
Highlights
Geothermal energy shows constant availability and stability regardless of changing weather conditions
To obtain a low degree of thermal conductivity, light additives are used to fill the cement slurry [16,17,18,19]. This is a challenge for engineers due to the restrictive requirements for cement slurries intended for sealing geothermal boreholes
The base cement slurry consists of cement, water and a defoaming agent which is a mixture of unsaturated fatty acid esters and refined hydrocarbons
Summary
Geothermal energy shows constant availability and stability regardless of changing weather conditions. To obtain a low degree of thermal conductivity, light additives are used to fill the cement slurry [16,17,18,19] This is a challenge for engineers due to the restrictive requirements for cement slurries intended for sealing geothermal boreholes. The fractionating cement slurry has a reduced density in the upper part of the borehole, and creates a cement sheath structure of such cement slurry, which has a high anisotropy This is very disadvantageous in geothermal boreholes, because the lower part of the borehole has inadequate thermal insulation. It allows you to determine the density of the cement slurry at individual points (top, middle, bottom) It is a very important measurement on the basis of which necessary modifications can be made to the composition of the cement slurry. Cement slurry of reduced density is designed, which is homogeneous and suitable for sealing geothermal boreholes
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