A geomechanical approach to solving the horizontal wells stability problem and increasing well productivity based on the physical modeling of deformation and filtration processes in the vicinity of the well is presented. The modeling was performed on a unique experimental facility Triaxial Independent Load Test System (TILTS) created at the Institute for Problems in Mechanics of the RAS. The importance of taking into account of the strength and filtration rock properties anisotropy is demonstrated on the example of Filanovsky field reservoir rock. The tests of rock specimens showed that rocks having the isotropic elastic properties and outward appearance can have significant anisotropy of strength and filtration properties. In this regard, fracture conditions of horizontal well vary for different circuit points, the fracture of a horizontal borehole begins in the areas near the intersection of well contour with the vertical plane. The rock permeability in the horizontal plane was significantly higher than in the vertical direction. Modeling of decompression process in horizontal downhole using TILTS revealed that the occurrence of non-uniform stress conditions in the vicinity of the well when creating a depression in its bottom may result to a substantial change in permeability in this zone – both to a decrease or an increase. The very significant permeability increase mainly observed in the test specimens corresponding to their location in the points of intersection of the contour of a horizontal well and a vertical plane.
The studies lead to the important conclusions regarding the selection of the prioritized strength and filtration properties of reservoir rocks to be determined experimentally under creating and filling in the geomechanical model of the deposit. Currently used traditional set of data is based on the assumption of an isotropic elastic and strength properties of rocks (Young's modulus, Poisson's ratio, the Mohr-Coulomb or Drucker-Prager strength constants, etc.). The facilities which based on the Karman principle mainly used to determine these characteristics, but they do not allow to create real stress conditions arising in the formations in the vicinity of the well. At the same time, deformation, strength and filtration properties of rocks depend intrinsically on the level and type of stresses created in the formation. Conclusions and forward recommendations to ensure the stability of rocks in the bottomhole zone of reservoir, find the maximum of allowable depression and well production can be quite remote from reality if the strength rock properties anisotropy, as well as the dependence of the filtration properties on stresses, will not be taken into account. And the central objectives to reduce risk and enhance efficiency in well production will not be achieved.
