Receptura zaczynu lekkiego do uszczelniania otworów w strefie niskich ciśnień złożowych

In the technology of sealing casing columns in a borehole, sometimes it is necessary to use cement slurry with reduced density. This occurs most often during sealing of the borehole in the low reservoir pressure zone. To design lightweight cement slurry, an addition of filler material is used, the density of which is much lower than the density of cement. However, the presence of such an additive in the structure of fresh cement slurry may sometimes cause destabilization of the system manifested by excessive fractionation, as a result of which light particles migrate to the upper parts of the cement slurry and heavy cement grains sink to the bottom. In addition, cement slurries containing light additives also show reduced values of mechanical parameters, greater porosity and capacity for gas migration, which may disqualify a given cement slurry for use in borehole conditions. In order to eliminate these adverse changes occurring in the structure of both fresh and hardened lightweight cement slurry, admixtures are used to significantly improve the technological parameters of the designed recipe. Appropriate selection, both quantitative and qualitative, of selected agents makes it possible to eliminate the cement slurry fractionation, as a result of which it is possible to obtain a homogeneous structure of the fresh cement slurry, and the cement sheath formed after setting will demonstrate the isotropic properties of the tested mechanical parameters. In addition, additives and low molecular weight admixtures allow sealing of the cement sheath matrix in such a way that the compressive strength is significantly improved and the value of permeability and porosity is reduced. The article discusses the results of research on the development of lightweight cement slurry recipes intended for scaling of openings in the zone of low reservoir pressures. As a control sample, a recipe was selected that had been used in well conditions. This cement slurry was selected for modification due to the lack of sedimentation stability. The following recipes contained various amounts of filling materials. As light additives, filter perlite, aluminosilicate microsphere and glass microsphere were used. However, two forms of silica were used to improve sedimentation stability and obtain appropriate mechanical parameters: a colloidal sodium silicate solution and hydrophilic nanosilica. The designed cement slurry recipes were characterized by appropriate technological parameters and sedimentation stability. The modifications introduced to the cement slurries allowed to achieve a homogeneous microstructure of the hardened cement slurry and an increase in the value of mechanical parameters was obtained. The developed group of recipes can be used to seal openings in the low reservoir pressure zone at a temperature of about 30°C and a pressure of about 3 MPa.