Water Well Journal
Issue link: http://read.dmtmag.com/i/655200
Michael: Rock or soil type is also a factor. The easiest drilling for directional rigs is a compact silty sand, but aquifers are found in a range of material types from boulders and cobbles to fractured bedrock. These can also be drilled, but sometimes with difficulty which can significantly increase the price. Gary: Lithology determines the type of drilling technique. So if it is in hard rock, one has to use air hammer. We do water rotary in softer formations. WWJ: What factors determine whether this method can be used? Gary: This is done in hilly and mountainous areas where one can drive the drill rig up to the hillside and drill horizontally. They can be drilled from 50 feet to 1000 feet and more. This is not directional drilling where rigs start out at an angle, go a certain depth, and then go horizontal. The well is drilled hor- izontal from the start. David: We drill slant wells, 12-foot diameter and larger, mainly for water supply wells in river basins. Since most of our wells are drilled next to the river, there are many factors to consider. There are setback issues—you have to deal with reg- ulatory agencies drilling in a floodplain. There's places on the Mississippi River where there's granite on both sides—we know there's gravel in the river bed but how do you get to it? Obviously vertical won't work, so you go horizontal. We sometimes do 6-inch test pilot wells to determine whether it will work. Michael: Depth of the well is an issue since it takes some hor- izontal distance to get to the desired depth. If your well is going to be 30 feet deep, it will take about 150 feet to achieve that depth, which is generally not an issue. However, if you wanted to put a well 500 feet deep, you would need to angle down for a horizontal distance of about 2500 feet to achieve your depth. Most sites don't have that much space available. The production requirements of the well can also be a fac- tor. If a large volume of water must be produced, it will drive the diameter of the well casing and screen, as well as the pump that must be used. There are limitations on screen diam- eter and well length that relate to the capacity of the drill rig being used for the installation. WWJ: What are some uses for angled wells? Michael: We primarily do environmental remediation work and have numerous examples of vertical well installations that did not effectively clean up the site, which was then success- fully remedied shortly after the installation of horizontal sys- tems. We installed a small horizontal system for a community on the Western Slope of the Rocky Mountains in Colorado where their primary water source was a spring on the side of a moun- tain. A horizontal well was installed that extended the spring piping and increased their flow. A vertical well would not even have been suitable in this situation since the system had no power available for pumps, and the horizontal well drained by gravity. Gary: Most jobs we get to drill horizontal wells, we have tried to drill vertically and found no water. It is more of a "last re- sort" approach. David: Our customers utilize this technology for water supply wells, generally either for municipal water supply or fracking water supply. I R D N A T TI D 5 - TI S T I N U G N LLI I et .n s e ri t s u d rin o l y a s@t e al s , O a uls . • T e v s A u h t an h X t r o 5 N 1 0 6 s e stri u d rin o l y a t t r visi o a n c o i t a m r re info o r m o F et .n s e ri t s u d rin o l y a t 30 1 4 K 7 et .n s , 1 0 3 -7 6 6 2 - 8 1 9 all: WWJ April 2016 31 Twitter @WaterWellJournl ANGLED WELLS continues on page 32