With the use of multi-fractured horizontal wells (MFHWs) now commonplace for the development of low-permeability (tight) and shale reservoirs, a premium has been placed on hydraulic fracture characterization methodologies that can be used to improve development efficiency. There are now multiple techniques that can be used to characterize hydraulic fractures during and after the stimulation treatment. Time-lapse seismic offers advantages over more conventionally-used microseismic because surveys can be collected before, during, and after stimulation treatment, providing the opportunity to observe reservoir system changes during the treatment. Further, seismic surveys can be more carefully designed because they don’t rely on passive signals from the reservoir. Finally, time-lapse seismic can be used to evaluate reservoir system changes in three dimensions and at larger scales than microseismic.
In this study, the impact of hydraulic fractures generated during stimulation treatment of two MFHWs on time-lapse seismic data is evaluated. The target reservoir is a low-permeability siltstone in the Montney Formation, western Canada. The objectives of this study are several-fold: 1) to analyze time-lapse multi-component seismic data collected during stimulation treatment in order assess the orientation and spatial position of hydraulic fractures; 2) to analyze compressional and shear velocity changes in the reservoir due to hydraulic fractures by performing time-lapse seismic inversion; 3) to compare different time-lapse seismic attributes to determine which ones are most consistent with independent fracture characterization methods, and 4) to evaluate the effect of flowback on seismic data.
This study demonstrates that time-lapse seismic attributes can be used to evaluate induced fracture location and orientation in the study area. It is further illustrated that PS seismic data are effective for characterizing the fractured regions due to the incorporation of shear wave (S) data along with compressional wave (P) data. Shear wave splitting maps provided partially consistent results with those of microseismic and other methods used to characterize the hydraulic fractures. Importantly, modeling performed herein demonstrates how velocities vary during flowback. The results of this study have important implications for the characterization of fractured zones in tight reservoirs.
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