Like HowStuffWorks on Facebook!

How Relief Wells Work

What a Relief: History of Relief Wells

Relief wells have been used since the early 1900s, nearly as long as machines have been tapping underground fossil fuels. Initially, relief wells were drilled vertically near a blowing well and used only to divert pressure from the well. Drilling techniques remained largely unchanged until 1933, when an angled -- or directional -- relief well was used in Texas. Not only did this relief well tap into the oil reservoir below a spouting well, but it also was used to kill the well by pumping water into its original source [source: Wright and Flak].

More improvements came in the 1970s and 1980s, when for the first time a relief well intersected with the underground pipe of a blowing well, thanks to improved detection methods. The era also introduced steerable directional drilling equipment and the use of fluids heavier than oil -- such as synthetic materials or natural materials including guar gum or mud -- to kill gushing wells [source: Wright and Flak]. Today, basic relief well techniques are still not much different from those used in 1933, although sophisticated drilling and detection equipment increase the odds that a relief well will hit its target -- whether that's a 6-inch (15-centimeter) diameter pipe or an underground reservoir [source: Spear]. The relief well either intercepts the original well's piping or taps into the reservoir from which the original well is pulling. It all depends on a rather complicated rubric that factors in, among other things, the probability of a well kill [source: Wright and Flak].

The use of relief wells to stabilize water-soaked earth became popular in the 1940s, when the U.S. Army Corps of Engineers used them to control excess water pressure near the Fort Peck Dam in Montana [source: U.S. Army Corps of Engineers]. This was done by drilling a well into the landward side of an embankment used to keep water from overflowing [source: Lucas]. That same year, relief wells became par for the course when it came to designing and constructing dams [source: U.S. Army Corps of Engineers]. Soon after, water relief wells also were used during residential and commercial construction to divert water or to help lower high water tables that could affect ground stability -- as is still done today [source: Cashman].

Most of the time, water relief wells are drilled as a precaution. When it comes to oil, some advocates recommend taking the same approach by drilling oil relief wells and regular wells simultaneously [source: Drash]. It's an idea that many experts say seems worth considering since relief wells often take two or three months to drill, depending on the depth of their location [source: Rubin]. In fact, a relief well may be finished long after the damage from a blowing well is done.

So, how exactly does a team of workers put a relief well into place? We'll explain it, step-by-step, on the next page.