Shear-wave splitting and attenuation analysis of downhole microseismic data for reservoir characterization of the Montney Formation, Pouce Coupe, Alberta

Two microseismic waveform analysis methods were performed for reservoir characterization of the Montney Formation at Pouce Coupe, Alberta. Microseismic events recorded on two downhole arrays during the hydraulic fracture stimulation of three production wells formed the dataset for both methods.;The first method involved the calculation of shear-wave attenuation factors through a comparison of observed and expected P/Sh amplitude ratios. The method was anticipated to help infer the presence of fluid-filled fractures however a number of limitations were identified. The assumption of a single source mechanism introduced significant uncertainty to the expected amplitude ratios. This uncertainty becomes increasingly amplified as source-vectors approach the modeled nodal planes, resulting in a strong azimuthal bias to the shear-wave attenuation factors. The accuracy of this method was also degraded by not accounting for variable baseline attenuation of the P- and Sh-waves. Future success with this method will likely require simultaneous surface and downhole microseismic monitoring such that source-mechanisms can be accurately determined for each event.;The second method performed was a microseismic shear-wave splitting analysis. A total of 48,987 3C seismograms yielded 1,136 reliable splitting measurements. Measurements indicate at least orthorhombic symmetry within the Pouce Coupe reservoir consisting of horizontally layered fabric and two near-vertical natural fracture sets roughly parallel and perpendicular to S HMax. This interpretation corroborates previous image log analysis from nearby Farrell Creek Field as well as focal mechanism and surface shear-wave splitting studies at Pouce Coupe.;A strong temporal correlation was observed between shear-wave splitting measurements and completion data. A continued increase in the magnitude of splitting during hydraulic stimulation coupled with a rotation of the fast polarization indicate that reservoir anisotropy becomes dominated by near-vertical hydraulic fractures roughly parallel to SHMax. Temporal observations made perpendicular to SHMax display a similar but less significant response at the onset of the completion process. This may suggest activation of the natural fracture set perpendicular to SHMax, but limited propagation of any hydraulic fractures in that direction.;This study highlights the value as well as some of the practical challenges associated with microseismic waveform analysis for reservoir characterization purposes. Future improvement of semi-automated analysis techniques that are adaptive to the waveform characteristics of individual source-receiver records will help make the most of large microseismic datasets for such purposes.