Discrete Element Modeling Applied to Laboratory Simulation of Near-Wellbore Mechanics

Abstract

Simulation results of near-wellbore failure phenomena are presented from a joint experimental-numerical study directed at developing a robust numerical simulation capability for the exploration and prediction of near-wellbore mechanics. An experimental procedure was developed for the laboratory simulation of slurry injection. A true-triaxial vessel, which applied realistic, three-dimensional stress conditions, was used to perform slurry injection into Berea sandstone. Under anisotropic horizontal stress conditions, vertical hydraulic fractures initiated and propagated in the direction of the maximum horizontal stress. Under isotropic horizontal stress conditions, multiple vertical fractures were induced and propagated in random orientation. A computationally efficient numerical model based on the discrete element method (DEM) is described and applied to simulate various wellbore phenomena. Radially graded, two-dimensional DEM models of the near-wellbore region were created of bonded disk elements. Source DEM elements were used to simulate fluid pressurization of the model borehole. The structural damage in the DEM models was analyzed using histograms of the angular distribution of bond damage. Results obtained for various stress states showed qualitative reproduction of the gross failure mechanisms associated with both hydraulic fracturing and borehole breakout.