Managing the Risks of Triggered Seismicity

It is well known that throughout the central and eastern U.S. there has been a marked increase in seismicity since 2009, at least some of which appears to increased wastewater injection.  No area has seen a greater increase in seismicity than Oklahoma. In this paper, we investigate whether, in practice, the utilization of information on stress orientation, relative stress magnitudes and the orientation fault can be used to identify the locations of potentially active faults. With such information, it is possible to make a determination of areas to avoid when evaluating sites of potential wastewater injection wells. While there are a number of sites where in situ stress data has been successfully used to identify potentially active faults, we are investigating whether this methodology can be implemented throughout a state utilizing the types of information available in areas of oil and gas development.  As an initial test of this concept, we have been compiling stress orientation data from wells throughout Oklahoma provided by private industry. Fifty new high quality data points, principally drilling-induced tensile fractures observed in image logs, result in a greatly improved understanding of the stress field in much of the state. A relatively uniform ENE direction of maximum compressive stress is observed, although stress orientations (and possibly relative stress magnitudes) differ in the southern and southwestern parts of the state. Our proposed methodology is being tested on the near-vertical NE-trending fault that produced at least one of the M 5+ earthquakes in the Prague, OK sequence in 2011, the Meers fault in southwestern OK, that produced a M~7 reverse faulting earthquake about 1100 years ago and several other areas of active faulting.