3D Numerical Mineral Mechanical Modeling of Fracture Propagation in Complex Reservoirs Rocks at Microscale

<p>Improved efficiency of hydraulic fracturing (HF) operations in complex reservoir rocks requires producing an extensive network of secondary fractures alongside the main fractures. The goal of the presented research is to find optimal stress-strain conditions yielding the most extensive network of secondary fractures at the microscale. The scope includes integrating results of microstructural characterization of tight gas reservoir rock samples and geomechanics. The study addresses the problem of hydraulic fracture optimization by suggesting stress-strain conditions to maximize fracture branching and, therefore, to optimize the drainage zone. We use a multidisciplinary approach including experimental data obtaining and numerical simulations. The first step is preparing a consistent set of 2D and 3D digital rock (DR) microscale models describing the experimental geometry, mineral composition and spatial distribution of mechanical properties of real rock samples. Geomechanical and petrophysical laboratory testing provide calibration/validation data for the DR models. Lab experiments include compressive and tensile strength testing coupled with digital image correlation, and X-ray computed tomography, 2D scanning electron microscopy coupled with mineralogy mapping. The preparation of DR models involves advanced 2D-to-3D and 3D-to-3D image registration techniques. The second step is a simulation of stress-strain states and fracture propagation in the models. We build simulation grids based on the mineral model and use a commercial mechanical simulator to simulate the fracture propagation at a microscale at given stress conditions. We applied the above approach to one of the most promising gas formations located in West Siberia, Russia. The reservoir rock features low permeability and pore dimensions down to tens of nanometers. Simulations delivered fracture networks for different loading conditions at the microscale. Simulation of typical geomechanical conditions allowed choosing reasonable stress-strain conditions that sustain the highest degree of formation fracturing. The research results may be applied to unconventional plays by increasing the efficiency of HF operation and maximizing production from isolated pore systems via establishing voids connectivity in the near-wellbore zone. The knowledge of the optimal stress-strain state for a near-wellbore zone will set the goal for HF propagation modeling at a wellbore scale. Using the approach, a geomechanical modeler would focus on designing main fractures, sustaining required stress-strain conditions in its vicinity, and thus producing the maximal amount of secondary microfractures. The results novelty is related with the simulation of 3D fracture propagation in highly heterogeneous reservoirs rocks taking into account its void space structure and fabric in geometry closest to real conditions.</p>