Two new technologies became popular after 1980. First, computer-controlled drill bits were used to bend the direction of new wells. Instead of going straight down, the wells could go down until a particular rock formation was reached and then the well could turn and run for miles parallel to the surface. Even if the well was not started exactly over an oil or gas deposit, it became more likely that the well would travel through a deposit at some point along the horizontal part of the well. Second, drillers learned how to fracture the rock next to the completion locations of the well. By making tiny cracks in non-porous rock, oil and gas that was trapped in those dense rock layers could flow into the well, just as if the rock was porous.
Fracking involves forcing a liberal large amount of a mixture of water, sand and special chemicals into the well at great pressure. The mixture has to go somewhere, so it finds the completion locations where there is a gap in the casing pipe and breaks up cracks into the surrounding rock layer. The pressure transmitted through the mixture fluid is like hitting the rock layer with a heavy hammer. If a producer tried to frack a vertical well, it would not produce very much petroleum, because only the oil and gas trapped within just a few feet of the well would be released by the small cracks. However, a horizontal well has many openings in the rock layer, making it possible for one well to release a lot of gas from the new cracks at the series of openings along the horizon portion of the well.
Because this new technology allowed the production of gas from non-porous shale rocks that had previously been considered to be undesirable for oil and gas production, the supply of onshore gas increased and the market price for gas dropped.