Correlations between formation properties and induced seismicity during high pressure injection into granitic rock

• Published in: Engineering geology Vol. 175; pp. 74 - 80
• Main Authors: McClure, Mark W., Horne, Roland N.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 10-06-2014; Elsevier
• Subjects: Applied sciences; Buildings. Public works; Exact sciences and technology; Fault development; Geotechnics; Geothermal; Induced seismicity; Rate and state friction; Soil mechanics. Rocks mechanics; Structure-soil interaction; Water injection; Fault development; Induced seismicity; Water injection; Geothermal; Rate and state friction; Project evaluation; Rock mechanics; Hydraulics; Stimulation; Fault; Seismicity; Granite; High pressure; Induced earthquake; Friction; Geothermy
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2014.03.015

We reviewed published results from six projects where hydraulic stimulation was performed in granitic rock. At each project, fractures in the formation were well-oriented to slip at the injection pressures used during stimulation. In all but one case, thousands of cubic meters of water were injected, and in every case, flow rates on the order of tens of liters per second were used. Despite these similarities, there was a large variation in the severity of induced seismicity that occurred in response to injection. At the three projects where induced seismicity was significant, observations at the wellbore showed evidence of well-developed brittle fault zones. At the three projects where induced seismicity was less significant, observations at the wellbore indicated only crack-like features and did not suggest significant fault development. These results suggest that assessments of the degree of fault development at the wellbore may be useful for predicting induced seismicity hazard. We cannot rule out that the differences were caused by variations in frictional properties that were unrelated to the degree of fault development (and it is possible that there is a relationship between these two parameters). The projects with more significant seismicity tended to be deeper, and if this is a meaningful correlation, it is unclear whether depth influenced seismic hazard through the degree of fault development, frictional properties, or some other variable. The results of this paper are not conclusive, but they suggest that there may be significant opportunity for future research on identifying geological conditions that increase induced seismicity hazard.
•Review of induced seismicity during hydraulic fracturing in granite at 6 sites•Severity of seismicity varies widely. Correlated to the degree of fault development•Another explanation may be variance in frictional properties.