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Uses of satellite image, magnetic and gravimetric analysis for early identification of fault reactivation risk - application to Utica field, Ohio

Abstract

The Utica is an unconventional field located in Ohio, the reservoir unit is an organic rich formation from upper Ordovician. This formation across the Appalachian basin from New York state to northeastern Kentucky, it covers 115,000 square miles, with a prospective area about 85,000 square miles. The structure and thickness of this formation are controlled by basement tectonic. In unconventional field’s development, drilling and injected water for hydraulic fracturing near a fault zone can be a major geo hazard. Faults and reactivated faults may act as migration pathway for the fracturing fluid, to lead to the contamination of fresh water aquifer. In Ohio, the 2011 Youngstown event is a clear example of fault reactivation inducing seismicity, early identification of this unknown fault would have allowed to minimize injection at its proximity. The purpose of this study is so to set up a methodology to reduce the risk of reactivating faults during the production of an unconventional field and to preserve fresh water aquifer. Seismic interpretation and imaging may give access to fault structural patterns identification. But, onshore seismic data can be very expensive to acquire at large scale. This study illustrate a method very accessible by using potential (gravimetric and magnetic) and satellite data to improve understanding of the local structural geology and identify faults. Combination of these two datasets constraint main faults locations in the Utica basin answer question which could have only been answer otherwise costly seismic acquisition. The study of the regional tectonic give the main stress orientation, here is ENE-WSW. The combination of the regional study and the geo satellite and potential analysis lead to a more precise identification of the main reactivation risk area by delineated them around faults with an ENE-WSW orientation. To validate this method, the risk area model has been compared to the seismicity history map of the Ohio and to the Youngstown case, an example of fault reactivation inducing seismicity. The correlation between the seismic events and the zones delineated with our approach is very strong, the majority of the seism are located in or around risk areas. So is the correlation with the Youngstown related seismic activity. This validation step show that the main reactivation risk zones could be predict quickly thanks to this kind of study leads with free data and bibliographic references.