Analysis of the Trajectory of a Hydraulic Fracture near the Seam Working and the Conditions for its Straight-line Growth


Annotation:

Model of the geomechanical state of a disc hydraulic fracture propagating in the solid rocks near the seam working is based on the methods of solid mechanics and fracture mechanics.
Stress field in the coal-rock mass containing in-seam working and growing hydraulic fracture was constructed as a result of solving an elastoplastic problem, in which the area of plasticity is the extremely stressed zones of the edge parts of the seam. The stress field in the edge parts was determined in the course of the numerical solution of three boundary value problems of the seam limiting state. The criteria for the onset of the limiting state are the general criterion of the Coulomb — Mohr limiting state for the formation and a special criterion for the limiting state for its contact with the rock mass. 
By replacing the extremely stressed zones with the stresses acting on their contact with the rock mass, the elastoplastic problem is reduced to the second external boundary value problem of the theory of elasticity, which is solved by the method of boundary integral equations.
At the relatively low fluid pressures in the pumping unit, the trajectory of the hydraulic fracture is a smooth curved line of the small length with a significant deviation of its ends from the direction of the seed crack.
With increasing fluid pressure, the crack length increases, and the deviation from the direction of the seed crack decreases. There are fluid pressures at which the crack propagates in a straight line and practically does not change its original direction. The straight-line trajectory of the crack in the vicinity of the working located at different depths corresponds to a point on the graph of the dependence of the relative length of the crack on the fluid relative pressure. This graph is a straight line.

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DOI: 10.24000/0409-2961-2021-5-18-23
Year: 2021
Issue num: May
Authors:
  • Cherdantsev N.V.
    Cherdantsev N.V.
    Dr. Sci. (Eng.), Chief Research Associate, nvch2014@yandex.ru Federal Research Centre of Coal and Coal Chemistry of SO RAN, Kemerovo, Russia