Large-Scale Chemically Pulsed Fracturing Stimulation of Unconventional Reservoir Using Hybrid FEM-DEM Approach

Abstract

In this paper, FDEM simulation approach was used to simulate the chemically-induced pulse fracturing of a large-scale wellbore confined by far field stresses. The mesh near wellbore is refined to maximize the model resolution in the critical regions, while coarser mesh elements are used in the regions away from the borehole to minimize the run time. The buildup of gas pressure generated by the reactive chemicals injected inside the borehole is applied to the borehole surface as a time-dependent surface pressure. Simulation showed that mixed tensile and shear fractures initiate from the borehole extending randomly towards the maximum horizontal stresses. These fractures continue to nucleate and eventually form an elliptical-shaped fracture region around the borehole. As the model undergoes more mechanical damage, shearing along the tip of the created fractures generate new shear fractures. As the pressure loading propagates, radial fracture is created and extended to into the model domain. Explicit deformation of rock near the wellbore is observed during the drilling process. The computational cost of large-scale dynamic simulation can be prohibitive. In this study the chemically pulsed fracturing processes in a large reservoir is investigated using FDEM approach, which optimizes the computational load while still accurately capturing an explicit deformation response of large rock rocks in the near-well regions using DEM and elastic dynamic response of rocks in the far-field using FEM.