Source-Mechanism Studies on Microseismicity Induced by Hydraulic Fracturing

Abstract

While microseismic mapping has proven to be a valuable technology for understanding hydraulic-fracture growth and behavior, the seismic waves generated by the microseismic event also contain information that has potential value for understanding the reservoir, natural fractures, stress state, and fracturing mechanisms. Extracting information from the microseismic data requires the use of a source model, which in its most general form is represented by a symmetric moment tensor having six components. Difficulties arise when attempting to invert for the components of the moment tensor if only a single monitor well is available, but in principle the full moment tensor can be extracted for multiple monitor wells. The primary information derived consists of the slippage-plane orientation, the slip direction, and the moment (strength) of the event. Presumably, these slippages occur on existing planes of weakness, such as natural fractures, bedding planes, or potentially even fracture planes induced by the hydraulic fracture, thus providing information about the reservoir and the process. An approach for performing the moment-tensor inversion is discussed for both single and multiple monitor wells, along with methods to estimate various parameters. Both synthetic and field examples are provided to demonstrate what can be extracted from the data set under various conditions.

The seismo-hydromechanical behavior during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in situ stimulation experiment

“…Welldocumented hydraulic stimulation datasets generally include microseismic observations as well as injection pressures and flow rates and, occasionally, tilt monitoring (Evans, 1983;Warpinski and Teufel, 1997). Although much information can be gained from these datasets, including imaging of microseismic structures (Niitsuma et al, 1999;Maxwell, 2014), energy balance between injected fluids and seismic energy release (Boroumand and Eaton 2012;Zoback et al, 2012;Warpinski, 2013), and source mechanisms (Jupe et al, 1992;Deichmann and Ernst, 2009;Warpinski and Du, 2010;Horálek et al, 2010), the constraints placed on the processes are insufficient to resolve details of the hydromechanical processes that underpin permeability enhancement, flow-path linkage, channeling or the interaction with natural fractures. Many of these processes possibly also depend on rock type.…”

“…Finally, the nature of the microseismicity generated by hydraulic fracturing is not adequately understood. Moment tensor analyses can offer insight into the nature of the failure in a microseismic event (Warpinski and Du, 2010;Eyre and van der Baan, 2015). For example, they can help resolve whether the seismic radiation is primarily generated by shear on preexisting fractures that are intersected by the propagating fracture, with relatively little energy generated by the advancing mode 1 tip of the hydraulic fracture (Sileny et al, 2009;Horálek et al, 2010;Rutledge et al, 2004).…”

Microseismic Imaging of Hydraulically Induced-Fractures in Gas Reservoirs: A Case Study in Barnett Shale Gas Reservoir, Texas, USA

“…Unfortunately few microseismic experiments in Barnett reservoir utilize two monitoring wells. A record of these wells ( Figure 5) was available to the present work for reevaluation in which approximately 30% of the recorded events was selected for detailed interpretation using moment-tensor inversion method described by Reference [31]. To recognize approximate radiation pattern of the microseismic energy a plot of the S/P ratio against the azimuthal position of approximately 100 good events is constructed and a theoretical solution is overlained on (Figure 6).…”

Full-waveform based microseismic source mechanism studies in the Barnett Shale: Linking microseismicity to reservoir geomechanics

“…However, recent studies have shown the existence of non-doublecouple (non-DC) mechanisms for some hydrofracture events (Šílený et al, 2009;Warpinski and Du, 2010). Knowledge of the complete MT, especially the non-DC components, is essential to understand the fracturing process especially the failure mechanisms (Šílený et al, 2009).…”

“…Consequently, the fracture can possibly be opened or closed during the rupture process. Tensile earthquakes have been reported in hydraulic fracturing and fluid injection experiments (Zoback, 2007;Šílený et al, 2009;Baig and Urbancic, 2010;Warpinski and Du, 2010;Song and Toksöz, 2011;Fischer and Guest, 2011). Moreover, field and experimental observations reveal that simple, planar hydraulic fractures, as commonly interpreted in many reservoir applications, are relatively rare (Busetti et al, 2012).…”