Microseismic events are monitored to understand the geometry of hydraulically induced fractures. In this paper, a geomechanical microseismic simulator that includes natural fractures is developed to (1) evaluate source information based on improved nonlinear solvers, (2) extend the solvers to solve large-scale fracturing problems, and (3) fully integrate 3-D geomechanical models with microseismic data for better interpretation.
A 3-D hydraulic fracturing simulator with fracture mechanics, fluid flow and the interaction between hydraulic and natural fractures in one system of equations is used to generate simulated microseismic events for a fracturing treatment. The limited far-field displacement (LFFD) method, is used to generate expected microseismic events. These are then compared with measurements and used to infer the geometry of the created fracture network. A computationally efficient forward and inversion model is used to conduct fracture diagnostics for source parameters. An inversion kernel function is defined to update estimated data and search for the optimal parameters that can provide the best match to the observed data.
Results for fracture diagnostics demonstrate insightful and interesting characteristics of both source mechanisms and nonlinear solvers served by the kernel function. The agreement between predicted microseisms and measured microseismic results is significantly improved by using either a particle swarm method assisted by two observation wells or the integration of particle swarm and Fmincon methods with one observation well. We observe a clear impact of natural fractures on the geometry and spatial distribution of microseismic events, which tend to be triggered along planes of weakness. We show how the configuration of observation wells affects focal mechanism estimations, since the determination of a reliable focal mechanism solution from multiple possibilities needs more coverage from observation wells.
The geomechanical microseismic simulator provides a tool to conduct fracture diagnostics and unveil high-resolution details of source mechanisms during hydraulic fracturing treatments.
Hydraulic fracturing is an essential technology for hydrocarbon and geothermal resources in naturally fractured formations. Usually, complex fracture networks, such as those observed in cores and mine-back experiments, are formed due to the abundance of pre-existing natural fractures in naturally fractured formations (Raterman et al., 2017; Gale et al., 2021). During the formation of these complex fracture networks, hydraulic fractures can alter stresses and pore pressures and induce some level of microseismicity (Albright and Pearson, 1982; Fehler, 1989; Warpinski et al., 2013). Microseismic monitoring, one kind of far-field monitoring, has been widely used to provide information about the generated fracture network. In this paper, an integrated geomechanics-fluid flow-seismicity model (forward model) is developed to evaluate source information based on improved nonlinear solvers and extended to solve large-scale fracturing problems.