The authors substantiated a need of evaluation the influence of thermobaric conditions on the rheological properties of magnesian cement slurries in oil and gas well casing with water-soluble salts. It is shown that measuring only slurry consistency and thickening time is not enough for estimating this influence. Measuring rheological properties, which are used for hydraulic calculations of cementing process, is necessary for choosing an optimum regime of oil-well slurry replacement in the annular space. For magnesian oil-well cement slurries, which rheological behavior is described by Bingham – Shvedov model, these properties are plastic viscosity and yield point.
A review of studies on the processes that occurs in oil-well cement slurries with temperature and pressure variation is accomplished. Methods and results of laboratory research, considered the influence of temperature and pressure on rheology of magnesian oil-well cement slurries, are adduced. Ranges of factors are chosen based on real conditions in oil wells where magnesian oil-well cements are used and on opportunities of instrumental base. The range of the temperature was 10-30 °C, for pressure – 0.1-14 MPa. Comparative results of evaluation of the influence of factors on rheology of portland and magnesian cement slurries are shown. It is established that temperature variation influences the rheological properties of magnesian oil-well cement slurries more than pressure variation. It is necessary to take into account both of these factors for choosing valid optimum regime of oil-well slurry replacement in annular space of well.
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