Earthquakes caused by injecting fluids underground similar to a tectonically active oil field

The extraction of gas and oil generates wealth – it can significantly boost the GDP of any country. But water is also extracted with hydrocarbons, often re-injected into the ground for disposal. Unfortunately, large-scale fluid injection can result in earthquakes1, which could lead to the termination of extraction before the full economic potential of the oil field is realized. In Nature, Hager and colleagues describe a multidisciplinary process for managing earthquake risk in an active oil field, maintaining the economic viability of a field that uses fluid injection to get rid of water, while reducing the potential for seismic activity strong enough to be felt by humans.

Worldwide extraction of hydrocarbons from both natural gas and petroleum liquids has increased steadily (see go.nature.com/3hnqdat) since the mid-1980s (although the COVID-19 pandemic has halted this long-term trend). The water generated during the process must be treated, recycled or disposed of, because it is saline and polluted with hydrocarbons and other organic and inorganic compounds3. Moreover, wastewater production tends to increase with the maturation of the oil field. This effect, combined with the continued increase in hydrocarbon extraction, means that wastewater disposal is an increasing global challenge.

Although most earthquakes are caused by tectonic forces, they can also occur by injecting fluids into rock, most commonly when fluids penetrate pre-existing faults. A concomitant increase in fluid pressures reduces the frictional resistance to slip, which in turn can reactivate the fault and trigger an earthquake (Fig. 1). The injection of fluids and the extraction of hydrocarbons can also cause significant changes in underground volume or mass that exert stresses on nearby and pre-existing faults, leading to seismic activity. In the past few years, various regions have experienced significant changes in earthquake frequency patterns due to large-scale fluid injection—including Oklahoma in the United States, the Sichuan Basin in China, and the Western Canada sedimentary basin. Such changes have been observed for fluid injection associated with dewatering and hydraulic fracturing (fracking)8.

Figure 1 | The mechanisms by which earthquakes can occur is by injecting fluids into oil and gas fields. a, Crude oil and gas extracted from a producer well contains polluted wastewater, which is often dumped underground by way of an injection well. If the collected wastewater is connected to a nearby fault, increasing the fluid pressure in the fault can reduce the frictional resistance to slip—which can reactivate the fault and cause an earthquake. Tectonic forces (red arrows) can contribute to this process. b, Fluid injection and hydrocarbon extraction can also cause significant changes in volume or mass that exert stresses (blue arrows) on core faults, leading to seismic activity. Hager and colleagues2 report a computational model of the Val d’Agri oil field in Italy that combines multiple data sources to simulate the effects of fluid injection and tectonic activity on seismic activity in that region. They use the model to estimate the maximum amount of fluid injection that can be tolerated without causing earthquakes strong enough for humans to feel. (Quoted from reference 1.)

Fluid flow simulations are typically used to investigate correlations between seismic patterns and fluid injection. This approach provides insight into the underlying drivers of earthquake occurrence in tectonically calm regions. However, fluid simulations alone are probably insufficient for developing earthquake management strategies, particularly in regions where tectonic earthquakes are common, because the predominant cause in such regions is explicitly ignored.

Hagar et al. They developed a multidisciplinary approach to earthquake mitigation in the Italian Val d’Agri field, which is located in a tectonically active region. Val d’Agri is the largest onshore oil field in Western Europe. Extraction began in 1993, and the field now accounts for more than half of Italy’s oil production. Wastewater disposal began in 2006 and resulted in about 300 small seismic events (a local maximum of 2.2, which is too small to be felt). Historically, an average of about four tectonic earthquakes of magnitude equal to or greater than 5.5 (strong enough to shake and possibly damage buildings) occur every century within 100 km of the fluid injection site. So what is a safe injection rate – that is, it is unlikely to result in significant seismic activity?

The authors developed a multi-step, process-based approach to address this question. First, they produced a 3D structural model of the Val d’Agri region, 80 × 50 × 10 km in size, containing 22 known major faults, surface topography, the top of the hydrocarbon reservoir and the rocks that enclose it. The model contains the entire Val d’Agri oil field and includes 24 active hydrocarbon production wells. Fluid flow is coupled with geomechanical processes in the model to replicate the effects of external tectonic forces, hydrocarbon extraction, and fluid injection from 1993 to 2016. Model parameters were estimated and calibrated using several data sources, including GPS data, well pressure records and inversion seismology (which uses seismic waves). reflexology to determine the structure of the Earth’s interior).

Next, the authors created a smaller 3D model, 13 x 13 x 15 km, comprising 17 faults and the producing wells in that region. This model focuses on a fluid injection well in an oil field and the associated earthquake sites. The dual modeling of fluid flow and geomechanical processes was again carried out using the larger model to constrain the behavior of the smaller model at its limits. Then the smaller model was used to assess the local stress and slip conditions at faults over time.

Simulations show that pressures have stabilized in most of the area around the injector well, because hydrocarbon extraction has reduced fluid pressure and thus increased slip resistance on most faults. On the contrary, the fluid penetrated a crack near the injector well, causing small earthquakes observed in that region. The authors then combined the smaller model output with earthquake physics models. They found that the results matched available observations of fluid flow within the hydrocarbon reservoir and observed seismic patterns – including dependence on past injection rates for the location, timing and evolution of earthquakes. The calibrated model indicates that a fluid injection rate of 2,000 m3/day, which is equivalent to 50% of the current total wastewater production, is unlikely to result in an appreciable seismicity above the tectonic background rate, while it is increasingly likely that Small events occur at rates above 2500 and 3000 m3/day.

Hager and his colleagues’ work is unusual for several reasons. Their method depends on the availability of detailed data and specialized knowledge of many aspects of the region and its wells. Unfortunately, it is unusual to have such detailed information. The authors’ findings are the product of a very fruitful partnership between academia and industry. As such, the results provide insights that may lead to the development of new industrial practices for managing and mitigating earthquakes from hydrocarbon extraction.

For example, a constant case of induced seismicity is the Groningen field in the Netherlands, which is the largest gas field in Europe. A gradual rise in seismic activity since 1991 in this region has caused property damage and led to increasingly frank public discontent, leading to the decision to end extraction in 2022. This would leave about 20% of the recoverable gas, worth about €70 billion (83 US$ billion), in the ground (see go.nature.com/3blwz2c). Applying Hager and colleagues’ method to this region may enable extraction of residual gas without causing further damage.

If the authors’ approach can be extended to include seismic activity associated with hydrocarbon extraction, in addition to those associated with wastewater injection, it may help to manage and mitigate associated environmental impacts if used in early stage earthquakes. Their method may also be suitable for managing earthquakes associated with carbon dioxide capture and engineered geothermal systems.

Phenomena associated with hydrocarbon extraction are often controversial13, but Hager et al. They developed a process for managing and mitigating one of the most important adverse effects: induced earthquakes. We hope this will help the oil and gas industry manage the balance between the economic viability and environmental impacts of extraction.

conflict of interest

The author receives research funding from the hydrocarbon industry.

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