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.