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Microseismic Event Location Trend and Their Relationship With Sequence Stratigraphy

Abstract

Microseismic event distribution is commonly interpreted as the geometry of a fracture network growth due to hydraulic fracturing. The event number, distribution pattern, and events cloud geometry are keys to evaluate the efficiency of the fracturing job. For this study, the interpretation of the relationship between microseismic event and sequence stratigraphy is based on the microseimic location data obtained by a ground survey while hydraulic fracturing of one horizontal well targeting the Woodford Shale (Devonian-L Mississippian, Oklahoma). The microseimic data has already been processed as 12 stages 1,552 events in total with reliable signal-to-noise ratio. A 4 square mile sequence stratigraphic framework was built by gamma ray log and scanned-cutting's XRF (X-ray fluorescence) profiles from a nearby vertical well and the hydraulic fracturing treatment well. Brittle and ductile zones were identified based on stratigraphic framework and Young's modulus/Poisson ratio. After filtering out the events outside of the Woodford interval, the distribution of microseismic events reveals that the events which represent growth patterns of fractures preferentially develop along the bed dipping trend and SHmax (maximum horizontal stress) direction of N78°E. About 60 percent of events or accumulated magnitude (calculated magnitude 3D model) are located within a Highstand System Tract and the number of events within brittle zones is twice the number as those within the ductile zones. This result indicates that there is a relationship between microseimic events location and regional stratigraphic framework of the Woodford Shale; fractures extend further horizontally and with higher density vertically within brittle zones and the Highstand System Tract. Asymmetric bi-wing event clouds at stage 5 and stage 6 of the horizontal well prove anisotropy exists on both sides of the wellbore. Future horizontal drilling is recommended to extend along SHmin which is S12°E and landing at the lower section of the TST.