Oil fields used to employ people only during the drilling phase. Once in production, they're mostly unattended. The classic oil field is a spread-out collection of pumpjacks running endlessly with nobody around.

Fracking operations, though, are complicated. There's usually a sizable site from which directional drilling spreads out underground. There's water, sand, and hydrochloric acid going down the holes, and mixed oil, gas, and sludge coming up. Lots of trucking activity.[1]

[1] https://www.fractracker.org/resources/oil-and-gas-101/explor...