1. Water that accompanies petroleum when it is brought to the surface from oil and gas wells is called “produced water.” From the beginning of the petroleum industry, it has been the practice to separate the produced water and return it to the earth. The injection wells are at depths far below the oil and gas producing wells and any drinking water or irrigation wells.
2. In very recent years, an increase in seismic activity has been correlated with an increase in the injection of wastewater into deep wells.
3. Expanded petroleum production made possible by newer techniques has gained access to formations that have very high volumes of water per barrel of oil. So even though the rate of oil production has been stagnant during recent times, the amount of produced water injected has risen substantially.
4. A credible theory is that the increased volume of wastewater injected into deep wells is “lubricating” existing faults, and thereby releasing the energy manifest as earthquakes. To be clear, there is no direct link to hydraulic fracturing (“fracking”), which is conducted much closer to the surface, other than the fact that it has made production from new, higher-water formations viable.