Passiveseismicmethodsforhydraulicfracturemonitoring:Resolvingfracturenetworks,slowslipandearthquakenucleationprocesses

DavidW.Eaton1,MirkovanderBaan2,MasonMacKay1,EnricoCaffagni3andMeganZecevic1

1DepartmentofGeoscience,UniversityofCalgary2DepartmentofPhysics,UniversityofAlberta

3InstitutfürMeteorologieundGeophysik.UniversitätWienHydraulic fracturing or stimulation methods are widely used for enhancing the permeability ofunconventionalhydrocarbonor geothermal reservoirs. Passive seismicmonitoring,using surfaceordownholesensorarrays,issometimesusedtomonitorthedistributionandcharacteristicsofinduced(micro)earthquakes. Within the process zone near the injection site, much of the recordedmicroseismicity is inferred to arise from activation of slip or tensile opening along pre-existingfractures,duetotheeffectsofbothporepressureandstressperturbations.Thereisongoingdebateabout whether this is also accompanied by slow-slip rupture processes, analogous to some faultsystems. In rare cases, basement faults have been activated by hydraulic fracturing, leading toinduced earthquakes. The applicationof template based-methods for event detection and locationareeffectiveforilluminatingfracturenetworksandunderstandingthedeformationprocessesinducedby the hydraulic stimulation. Similar techniques show promise for resolving small-scale nucleationprocessesassociatedwithfaultactivation.Perspectiveviews(left)anddepthsections(right)showingmicroseismicityfromthefirst4treatmentstagesofhydraulicfracturinginalow-permeabilityreservoir(EatonandCaffagni,2015,FirstBreak,33(7),49-55).Panels A and B show the results from initial commercial processing; C,D show results using a matchedfilteringmethod.

Acknowledgement: This work was supported by the Natural Sciences and Engineering Research Council ofCanada(NSERC)andbysponsorsoftheMicroseismicIndustryConsortium(www.microseismic-research.com).