Analysis of the microseismicity induced by a fluid injection in a granitic rock mass

Abstract

The microseismicity induced by a fluid injection at a depth of 443 m in a granitic rock mass has been monitored with a 16 station network. The location of the five events observed on the near totality of the network suggests that flow away from the well occurred along a preexisting fracture nearly parallel to the maximum horizontal principal stress direction and not along the fractures observed at the wellbore. Focal mechanisms of these events are coherent with shear motions along fissures which intersect the main flow path. A difficulty has been encountered in the determination of source parameters from spectral analysis of signals because of attenuation effects. Indeed, for uncorrected spectra the corner frequency was found to decrease as the source to station distance increased. This demonstrates the effect of attenuation on the signals and therefore the necessity of correcting spectra for attenuation effects before estimating source parameters.

Mechanical and hydraulic coupling of injection-induced slip along pre-existing fractures

“…Injection-induced slip in fractures is understood to be one of the mechanisms causing the microseismicity observed during hydraulic stimulation (Pearson, 1981;Pine and Batchelor, 1984;Talebi and Cornet, 1987;Cornet and Yin, 1995), that has been associated with fluid injection within a number of different geological environments, including geothermal reservoirs (Pearson, 1981;Pine and Batchelor, 1984;Niitsuma et al, 1999;Baisch et al, 2006aBaisch et al, , 2006bMajer et al, 2007), oil/gas reservoirs (Phillips et al, 2002;Rutledge and Phillips, 2003;Rutledge et al, 2004), crystalline rocks (Zoback and Harjes, 1997;Baisch et al, 2002), and active faults (Tadokoro et al, 2000(Tadokoro et al, , 2001. Since induced seismicity and its role in the creation or enhancement of geothermal reservoirs have recently been the subject of debate (Bommer et al, 2006;Majer et al, 2005Majer et al, , 2007, it is to be hoped that a better understanding of the mechanisms of change in fracture permeability associated with induced slip events will provide information of fundamental significance for future interpretations of the relationship between fluid flow and microseismicity.…”

SH Propagator Matrix and Qs Estimates From Borehole- and Surface-Recorded Earthquake Data

“…Hauksson, Teng & Henyey (1987) used a three-level downhole array to study site responses, local quality factors and cut-off frequencies of acceleration spectra. Talebi & Cornet (1987) monitored fluid injection induced microseismicity in a granitic rock mass. Malin et al (1988) analysed velocity spectra and particle motion as a function of depth.…”

Source Parameters of Injection-induced Microseismicity

“…Since the observation of this phenomenon at Denver (HEALY et al, 1968), Rangely (RALEIGH et al, 1972) and Matsushiro (OHTAKE, 1974), similar observations at smaller scales have extended this conclusion to quite smaller microseismic events, particularly when clear evidence of a double-couple source was provided from fault-plane solutions (e.g., CASH et al, 1983;TALEBI and CORNET, 1987). Other types of possible source mechanisms are related to the sudden extension of hydraulic fractures in tension and complex interactions of fluid and solid phases, considered to be at the origin of long-period events that show similar characteristics to volcanic tremors (BAME and FEHLER, 1986).…”