The Uniqueness of Microseismic Monitoring

Microseismic monitoring is synonymous with shale gas development in North America: experience with shale plays suggests a high degree of variability in rock properties, subsequent completion effectiveness, and ultimately gas production and EUR. There are several modes of acquisition currently in use to obtain microseismic information which is related to the hydraulic fracturing process. The study reported here focuses on borehole microseismic and attempts to understand the information content in ‘conventional’ monitoring practice available in the industry. It examines the sensitivity to velocity model and uncertainty in derived data and attributes. Four stimulations and two monitor wells provide 12 multi-stage datasets for repeated analysis. Monitoring with a single well tends to produce bias in results towards the observation. Further, we see that a horizontal monitor provides different controls on locations to a vertical monitor, but their combination in a dual-well solution usually produces the more consistent view. As we change the velocity model, we see more variation in located events for the same input data (extent in 3D and possible orientations). The interpretation of these results in terms of hydraulic fracture characterization and effectiveness is therefore non-unique, and this uncertainty should be recognised.