In a series of stages of creating insulation in a well in the form of a cement ring, the most critical and least studied is the stage of the beginning of the hardening of the cement slurry behind the casing. It is proved that during this period the pressure of the solution column at the bottomhole decreases and conditions arise for the influx of reservoir fluids into the well and the formation of behind-the-casing flows. It is difficult to simulate these processes in the laboratory, and it is expensive to observe in the well. Therefore, mathematical modeling can be a significant addition to their understanding.
In the article, solutions are given to boundary value problems of an equation describing the process of the fall of the “hydrostatic” pressure of cement slurries in a well with impermeable walls even when the cement mortar column hardens in contact with the permeable formation with a given pressure of fluid. Using the formulas obtained, the pressure distribution curves of the cement slurry over the depth of the well and over time were constructed according to which pressure gradients operating during the waiting on cement period in the annular space of the well were calculated. The criteria for the resistance of cement slurries to the introduction of formation fluid in them to the formation of behind-the-casing flows through hardening cement mortar are formulated. Comparison of pressure gradients acting in the well with the criteria for cement slurry resistibility allows calculating the size of the zones of suffusion fracture of the structure of cement suspensions by formation fluid in the annular space during waiting on cement.
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