Numerical Study of the Influences of Dynamic Loading and Unloading Rates on Fracturing
Conference Paper
Overview
Research
Identity
Other
View All
Overview
abstract
ABSTRACTDynamic loading offers the potential to induce densely connected fractured pore space over large bulk volumes of impermeable rock. An understanding of the impacts of the dynamic loading and unloading rates on the resulting fracturing can guide the design of discharge technologies. This work numerically investigates the dependence of the extent of fracturing on dynamic loading characteristics. We reconcile a high-fidelity model (finite-discrete element method with nonlinear fracture mechanics) with experimental observations. The model is subsequently used to simulate various loading scenarios spanning laboratory to field scale conditions.INTRODUCTIONIn contrast to hydraulic fracturing, high-energy dynamic loads generate radial fractures which are not influenced by formation stress anisotropy. This removes the need for determining the in-situ stress orientation, which is a necessary factor in designing horizontal wells that undergo multiple hydraulic fracturing treatments. This study aims to investigate the effect of different dynamic load functions on seismic fracturing.One way to create high-energy dynamic loads is to use explosives (e.g., Grady et al. (Grady et al., 1980), Banadaki et al. (Banadaki, 2010), Zhang et al. (Zhang et al., 2017), and Jeong et al. (Jeong et al., 2020)). Explosives generate loading pulses with a maximum peak pressure that can exceed 1 GPa and a rise time of the pressure waveform on the order of 1 to 2 microseconds. Experiences using explosives are well-documented and span applications in various materials like granite, shale, and PMMA. The body of reported experiments shows that the extent of crack propagation depends on the energy released by the explosive charge, although a quantitative understanding of this relationship remains elusive for formations in the deep subsurface which cannot be observed directly or with great resolution. Another type of technology delivers the dynamic load using shock waves created in liquid. Hamelin et al. (Haimson and Fairhurst, 1967), Maurel et al. (Maurel et al., 2010), Chen et al. (Chen et al., 2012), and Xiao et al. (Xiao et al., 2018) for instance, applied Pulsed Arc Electrohydraulic Discharges (PAED) to produce shock waves in water. These loading profiles typically involve a longer time for the load to reach its peak. Moreover, in the case of laboratory experiments, reflections of shock waves from the finite samples may create extra fractures. To study the potential of formation fracturing at the field scale, large sample sizes, a wide variety of high energy loadings, and accurate diagnostics are needed. Given the challenge and costs of such extensive experimentation, numerical simulation can offer a useful alternative to narrow down the range of pulses to be investiated.
