The vast majority of tight oil and shale gas formations in the US are using horizontal wells for production, according to the Energy Information Administration (EIA).

About 15 years ago, horizontal wells made up 15% of crude output and 14% of natural gas production in shale plays. In 2018, that percentage jumped to 96% and 97%, respectively.

Horizontal wells surpassed the number of vertical wells in US shale formations in 2017. Although around 88,000 vertical wells continue producing, the EIA said the wells are “considered marginal, or stripper, wells, which will continue to produce small volumes until they become uneconomic.”

The use of horizontal wells in tight oil and shale gas plays became the dominant source of production in 2008 and 2010, respectively, the EIA said.

In the prolific Permian shale play of west Texas and south-east New Mexico, vertical wells accounted for about half of output as late as 2014. By 2018, that figure had dropped to 7%.

In the Appalachian basin, the Marcellus shale gas formation now produces almost entirely - 99% - from horizontal wells.

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Horizontal wells dominate