Seismicity in the Oil Field

Seismicity in the Oil Field by Vitaly V. Adushkin. Vladimir N. Rodionov. Sergey Turuntaev. Institute of Dynamics of Geospheres,. Russian Academy of Sciences, 2000. Much of this article originally appeared in the Schlumberger Russian version of the Oilfield Review, Neftegasovoye Obozreniye 5, no.1 (Spring 2000): 4:15. Results in this article were based on data obtained by the local seismic network of Stock Joint Company “Tatneft.” The authors thanks I.A. Iskhakove, head of the TNGF seismic crew and K.M. Mirzoev, chief of the Tatarstan seismic survey, who provided the catalogue of seismice events and the produced and injected fluid volumes data. The support from “Tafneft” and the Russion Foundation for Basic Research (RFBR project #98-05-64547) is gratefully acknowledged.

The gas field was discovered in 1956 and production began in 1962. Over the next 14 years, roughly 600×106 m3 of water, or 106 ton per km2, were injected. …

Beginning in 1976, a series of large earthquakes was recorded. The first significant earthquake occurred on April 8, 1976 at a distance of 20 km [12 miles] from the Gazli gasfield boundary. The earthquake magnitude measured 6.8. Just 39 days later, on May 17, 1976, another severe earthquake occurred 27 km [17 miles] to the west of the first one. The magnitude of the second earthquake was 7.3. Eight years later, on March 20, 1984, a third earthquake occurred 15 km [9miles] to the west of the second earthquake, with a magnitude of 7.2. … Aftershocks occurred in a volume surrounding the three hypocentres. These earthquakes are the strongest of all the known earthquakes in the plain of Central Asia. …

There was no clear relationship between the location of the earthquake hypocenters and any previously known active tectonic structures.

Closer investigation showed that the earthquakes had created new faults.

… In all these cases, the result of human interference was to change the state of stress in the surrounding volume of earth. If the stress change is big enough, it can cause an earthquake, either by fracturing the rock mass—in the case of mining or underground explosions—or by causing rock to slip along existing zones of weakness.

The situation in regions of hydrocarbon recovery is not always well understood: in some places, extraction of fluid induces seismicity; in others, injection induces seismicity.

Even minor actions can trigger strong seismicity.

… The amassed data indicate that the Gazli earthquakes were triggered by the exploitation of the gas field.

In regions of high tectonic potential energy, hydrocarbon production can cause severe increases in seismic activity and trigger strong earthquakes, as in Gazli, Uzbekistan.

In regions of lower tectonic stress, earthquakes of that magnitude are less likely, but relatively weak earthquakes could occur and damage surface structures.

[Refer also to:

Producer admits fracking causes “very small earthquakes” ]

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