Simultaneous microseismic event localization and source mechanism determination

Abstract

Microseismic monitoring has become a tool of choice for the development and optimization of oil and gas production from unconventional reservoirs. The primary objective of (micro) seismic monitoring includes localization of (micro) seismic events and characterization of their source mechanisms. Most seismic events are of a nonexplosive nature, and thus, there are waveform (polarity) differences among receivers. Specifically, double-couple sources represented a challenge for migration-based localization techniques. We developed and applied a new migration-type location technique combined with source mechanism inversion that allowed for constructive interference of signal in seismic waveforms. The procedure included constructing image functions by stacking the amplitudes with compensated polarity changes. The compensation weights were calculated by using moment tensor inversion. This method did not require any picking of arrivals at individual receivers, but it required receivers to be distributed in multiple azimuths and offsets. This made the technique suitable for surface or near-surface monitoring, in which a low signal-tonoise ratio (S/N) can be overcome by stacking. Furthermore, the advantage of this technique was that in addition to the position in time and space, we also determined the source mechanism. We determined with numerical tests that the proposed technique can be used for detection and location of events with S/Ns as low as 0.05 at individual (prestacked) receivers. Furthermore, we found that other source mechanism parameters such as magnitude, volumetric, or shear components of the source mechanism were not suitable for the location. Finally, we applied the proposed technique to a microseismic event of moment magnitude −0.3 induced during the hydraulic fracturing treatment of a gas shale reservoir in North America.

Full Waveform Seismological Advances for Microseismic Monitoring

“…This approach was later successfully adopted for the investigation of regional seismicity in different regions (Guilhem & Dreger, 2010;Tsuroka, Kawakatsu, & Urabe, 2009). Following this general idea, a growing number of recent works attempt to achieve a similar joint inversion of location and moment tensor for microseismic events (Anikiev, Valenta, Stanek, & Eisner, 2014;Chambers, Dando, Jones, Velasco, & Wilson, 2014;Gharti, Oye, K€ uhn, & Zhao, 2011;Kawakatsu, 1998;Krieger, 2011;Vera Rodriguez, Sacchi, & Gu, 2012;Weber, 2006;Zhebel & Eisner, 2012), revealing the extreme interest in this type of applications for microseismicity monitoring and characterization. In fact, although a joint detection, location, and source parameter inversion modeling high-frequency signals is very demanding and requires the simultaneous determination of many unknowns, the large size of microseismic monitoring networks and the often available 3D network geometries are helpful to resolve this challenging inversion problem.…”

Velocity model optimization for surface microseismic monitoring via amplitude stacking

“…To study the impact of noise on the two methods, we added the low frequency noise which is similar to the effective signal frequency to synthetic data to generate S/N = 0.1 (Fig. 7), where S/N is defined following Zhebel and Eisner (2015): i.e.…”

“…In recent years, migration-based amplitude stacking techniques for microseismic monitoring from the surface have been gradually developed (Anikiev et al, 2007, Lu and Zeng, 2012, Zhebel and Eisner, 2015, Chambers et al, 2014. These techniques do not require first arrival picks at individual receivers, and can resolve velocity models using data with much lower S/N values than those of borehole arrays.…”

“…Changes in fracture pressure, which are related to hydraulic fracture stimulation, cause a series of microseismic events in the reservoirs around the perforation shot (Warpinski et al, 2005). We can evaluate the fracturing effects (Eisner et al, 2010;Maxwell et al, 2010;Maxwell and Urbancic, 2002;Phillips et al, 2002) and determine the fracture propagation trend and source mechanism (Anikiev et al, 2014;Trifu et al, 2000;Zhebel and Eisner, 2015) using microseismic location and monitoring technology. However, efficient resource extraction requires accurate reservoir characterization, a key component of which is accurate locations of microseismic events.…”

Weighted-elastic-wave interferometric imaging of microseismic source location

“…The simulation parameters are space of 2.5 m, time interval of 0.5 ms, and a 60 Hz ricker wavelet function, which is a horizontally excited force source. Owing to the source size that is much smaller than the fracture length, we use point sources to simulate the microseismic sources (Zhebel and Eisner, 2012). In the two numerical experiments, the source is located at point (250 m, 250 m) and monitored by surface and downhole arrays with 51 geophones.…”