Induced seismicity issue grows
You might think that induced seismicity is a growing topic in our industry and, of course, you would be spot on. But recently, the conversation has turned back in time. According to Alicia Chang of the Associated Press, published in the Nov. 1 issue of the Houston Chronicle, new research suggests that oil and gas drilling, more than eight decades ago, might have triggered earthquakes in the Los Angeles area, including a 1933 quake in Long Beach that killed 115 people and toppled structures, including schools.
In the study by the United States Geological Survey (USGS), seismologist Sue Hough and colleague Morgan Paige assembled a list of quakes in the area between 1915 and the early 1930s, together with drilling data from that period. Their analyses produced 13 instances, in which seismic events might have been related to drilling and production. The full findings appear in the Bulletin of the Seismological Society of America.
![Fig. 1. Stress map of Texas, showing maximum horizontal stress (SHmax) orientations and faulting regime, categorized using the Aφ system of Simpson [1997] (see text for details). Basin boundaries are from the U.S. Energy Information Administration. The Rio Grande Rift boundary was compiled from Seager and Morgan [1979] and Perry et al. [1987]. Source: State of stress in Texas: Implications for induced seismicity, Jens-Erik Lund Snee and Mark D. Zoback, Department of Geophysics, Stanford University, Stanford, Calif., 2016.](/media/5567/wo1216-advisor-section-pike-fig-01.jpg)
A bit more startling is a paragraph in Chang’s article noting that, earlier this year, “Cliff Frohlich, a senior research scientist at the University of Texas at Austin, found that earthquakes resulting from oil and gas operations in Texas have been happening since 1925, much earlier than previously thought.”
As you all know, the trend in induced seismicity has continued and broadened. And, as it has broadened, and continues to broaden, so has the public’s belief that there is a strong correlation between oilfield activities (primarily fracturing) and induced earthquakes. As noted at an induced seismicity workshop at New Mexico Tech in 2014, this is at odds with the “science community’s more cautious, evidence-based approach, which mostly sees brine injection wells as the problem, in the few places that problems exist.”
The resolution of these misconceptions, in the workshop’s estimation, requires a continued presentation of solid science, together with the gathering of more scientific details. Fortunately, that is what is happening. Below, two examples of solid scientific research into induced seismicity are discussed.
One of those studies was undertaken by Jens-Erik Lund Snee and Mark D. Zoback in the Department of Geophysics at Stanford University. An interesting aspect of the research was the creation of a detailed “stress map” of Texas. Stress measurements gathered in the study “reveal a complex but spatially coherent stress field in Texas, which allowed” the researchers “to better understand the triggering mechanisms of past earthquakes and characterize the seismic hazard across the area.”
The authors concluded that, “although Texas is relatively seismically quiescent, several recent earthquakes are suspected to have been triggered by industrial (read oil and gas) activities (near Snyder/Cogdell, Karnes City/Fashing, the Dallas-Fort Worth metroplex and Timpson). These earthquakes have nodal plane geometries consistent with the observed stress field, indicating that they are occurring on faults that are already likely to be active.”
Snee and Zoback’s research is complemented nicely by Frolich’s work, much of it focused on the areas that Snee and Zoback investigated. Further work in the arena—focused primarily on the Permian basin—has been undertaken by Harold Gurrola, professor of seismology in the Department of Geosciences at Texas Tech University, among others.
The similarity in foci and conclusions among these sources was integrated well by Brandon Mulder in the Nov. 14, 2015, issue of the Midland Reporter-Telegram. In it, Frohlich notes that “nearly two-thirds of all Texas earthquakes have occurred in/near petroleum fields, or near injection disposal wells.
“The linear pattern of the quakes in the areas indicates a fault system known as the Llano Front, according to Gurrola, that runs from about Van Horn, through Snyder and up to central Oklahoma, where hundreds of quakes have stirred Oklahoma City.” That fault system, and others, are ripe for activation. As Gurrola put it in the Reporter-Telegram article, “with a really big earthquake, you’re really talking when, not if. If a 7.0 happens because of fluid injection, it was going to happen anyway. If a 3.0 happens because of fluid injection, it might not have happened.”
With some 144,000 brine injection wells receiving about 47 MMbpd, the public dialogue on the issue of induced seismicity is not nearly finished, but there is hope. A recent study by Nicholas van der Elst of the U.S. Geological Survey shows that the gravitational forces between the sun and moon can trigger a special kind of earthquake on the San Andres Fault. So, I say we blame the heavens. 
