Extraction of Coal, Oil, and Natural Gas

Coal sits in seams close enough to the surface or underground that it can be dug or mined directly. Oil and natural gas are different: they're often trapped in rock pores too tight for them to flow out on their own. Hydraulic fracturing solves this for shale gas. A well is drilled down, then often turns horizontal to travel through the gas-bearing shale layer. Water mixed with sand and chemicals is pumped down at extremely high pressure, enough to crack the dense rock. The sand grains wedge into those new cracks, propping them open after the pressure is released. Gas trapped in the rock now has a path to flow through the cracks, into the well, and up to the surface.

Offshore drilling reaches oil differently. A platform anchors over the site, and a well bore is drilled down through kilometers of seawater, then further through rock, down to a reservoir. Steel casing lines the well to keep it stable and to separate the oil and gas from surrounding rock and groundwater. If that casing fails near a fracking site, fluids or gas can migrate into aquifers, contaminating drinking water with chemicals or methane. This is the main environmental risk tied to extraction itself, separate from burning the fuel.

This topic sets up why extraction has costs beyond carbon emissions: fracking uses huge volumes of water and can trigger small earthquakes, while drilling and transport create spill risk. The next topics in the unit price these costs against the energy gained, using efficiency and conversion math to compare fossil fuels to alternatives.