Abstract
Oilfield wastewater disposal causes fluid pressure transients that induce earthquakes. Here we show that, in addition to pressure transients related to pumping, there are pressure transients caused by density differences between the wastewater and host rock fluids. In northern Oklahoma, this effect caused earthquakes to migrate downward at ~0.5 km per year during a period of high-rate injections. Following substantial injection rate reductions, the downward earthquake migration rate slowed to ~0.1 km per year. Our model of this scenario shows that the density-driven pressure front migrates downward at comparable rates. This effect may locally increase fluid pressure below injection wells for 10+ years after substantial injection rate reductions. We also show that in north-central Oklahoma the relative proportion of high-magnitude earthquakes increases at 8+ km depth. Thus, our study implies that, following injection rate reductions, the frequency of high-magnitude earthquakes may decay more slowly than the overall earthquake rate.
Highlights
Oilfield wastewater disposal causes fluid pressure transients that induce earthquakes
We tested the implications of this observation by modeling salt water disposal (SWD) operations for a typical highrate (2080 m3 day−1) SWD well in Alfalfa County
1.63 and 1.28 at depths less than 8 km, and systematically decreases to 0.87 between 8 and 10 km depth (Fig. 5b). These results are in general agreement with Mori and Abercrombie[31], who found that the b-value for earthquakes in northern California systematically decreases from 1.28 between 0 and 3 km Injection-induced earthquakes are caused by fluid pressure transients that decrease effective normal stress on optimallyoriented faults
Summary
Oilfield wastewater disposal causes fluid pressure transients that induce earthquakes. Number M2.5+ earthquakes a he recent boom in unconventional oil and gas production across the midcontinent United States caused a sharp increase in the rate of oilfield wastewater production This wastewater is discarded by pumping it into deep geologic formations via salt water disposal (SWD) wells[1,2]. One landmark modeling study found that several high-rate SWD wells in southeast Oklahoma City produced a fluid pressure front that accurately matched earthquake hypocenter locations leading up to the Jones earthquake swarm[8]. This historymatching approach was repeated in more recent studies linking. At pressure and temperature conditions representative of ~5 km depth (50 MPa and 100 °C)
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