Exploring the connections between injection wells and seismic migration patterns is key to understanding processes controlling growth of fluid-injection induced seismicity. Numerous seismic clusters in Oklahoma have been associated with wastewater disposal operations, providing a unique opportunity to investigate migration directions of each cluster with respect to the injection-well locations. This study focuses on new strategies to identify and quantify lateral migration toward or away from the injection wells. First, a comprehensive migration analysis is described to reach a representative migration vector for each seismic cluster. Next, we propose a new approach to define a well vector associated with multiple injection points, taking into account cumulative injected-volume and the injection-rate volume weighting, and considering also the expansion of the diffusion front. Injected fluids can be associated with an earthquake cluster only if they have sufficient time to reach the location of the cluster. Finally, new directivity migration parameters are introduced comparing the direction of migration and well vectors. Our results suggest a relationship between migration patterns and the cluster-well distances, but unclear relationship with injected volume and equivalent magnitudes. At shorter distances (up to ~13 km), we observe dominantly migration away from injection wells (particularly for distances shorter than ~5 km) that could be attributed to pore-pressure changes. However, we also find an opposite behavior, migration toward the wells, for larger distances, suggesting an increasing influence of poroelastic stress changes. This finding is more stable when considering cumulative injected-volume instead of injection-rate.
|Original language||English (US)|
|Journal||Bull. Seis. Soc. Am.|
|State||Published - 2020|