Factors Influencing the Surface Expressions of Perforation Shots

A Fayetteville shale stimulation concurrently monitored using a surface seismic array and a wide aperture downhole array is analysed in order to develop a better understanding of the factors influencing the surface expression of perforation shots using a combination of data processing and forward modelling. The perforation shots typically give rise to multiple compressional and shear wave arrivals. A comparison of observed and modelled arrivals reveals the importance of two geological parameters: a 1.6 degree subsurface dip, which had been neglected in previous studies, and a strong Thomsen anisotropy in the Fayetteville shale, typically between 40% and 50%. Of equal importance are shot generated waves (tube waves) travelling through the treatment well which interact with plugs remaining in the well and give rise to secondary high amplitude, low frequency, seismic events. These arrivals, which are related to source, propagation and treatment operation effects, need careful separation and interpretation in order to allow the reliable derivation of velocity models for surface microseismic monitoring.