Water Well Journal

March 2016

Water Well Journal

Issue link: http://read.dmtmag.com/i/643500

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Page 48 of 85

W hen one refers to "straight hole drilling" what is one really referring to? It should be a set of well-written specifications that includes a plumbness and alignment section. Plumbness and alignment are two completely different aspects and both may affect the performance of the well or the ability of the drilling contractor to complete the well in a manner acceptable by today's standards. First, plumb or plumbness refers to the deviation from a 100% true vertical line. The Merriam-Webster definition of plumb is "exactly straight down or up: in a perfectly vertical position." Why is this important in a well? If the well is not truly plumb, the pump when installed will lean up against the side of the casing. This is especially true for line shaft turbines. If a sub- mersible is installed, plumbness is critical to prevent the sub- mersible wire from being rubbed against the side of the casing and wearing a hole in the jacket of the cable, thus causing the pump to short out. With a line shaft turbine, a shaft runs from the motor on top of the well to a set of bowls below; an out of plumb well will cause stress to be placed on the bearings and cause pre- mature failure of the pump shafts. Starting Right When one starts the construction of a new well, it is vitally important to start the new wellbore plumb. There are many ways to do this. A method we have used and found successful is to create a "table" in the drill that allows for various sizes of round stabi- lizers to be guided through as the hole is being started. This setup is only applicable to top-head drills. The size of the well one is going to drill will dictate the table opening for the stabilizer. Our rigs have table guides from 6.625 inches to 18 inches and we will use a table guide for the applicable size of stabilizer. For example, if we are going to start a 12.25-inch hole, we will use a stabilizer that is 11.75 inches outside diameter. When we start the hole, we install the stabilizer into the table guide and put a 4-foot level on the stabilizer on various sides of it and move the jacks until the stabilizer is level on all sides. We then drill the hole down to a point where the stabi- lizer is below the table and then install the appropriate-size table guides based on the drill rod diameter. Depending on the formation we are drilling through, we may switch stabilizers to a bladed stabilizer if we are drilling through unconsolidated formations, or switch to a twisted sta- bilizer if we are drilling through consolidated formations. Starting the hole in this manner doesn't guarantee a truly plumb well, and almost all wells are not truly plumb as it is nearly impossible to achieve a truly straight well. The stan- dard requirement for most specifications is to allow for the deviation from plumb up to two-thirds the diameter of the well casing per 100 feet of depth. For example, if you are drilling a 10-inch well, you will be allowed to be off at 100 feet 6.6 inches from plumb, and at 200 feet depth 13.2 inches from plumb. Using stabilizers with heavy drill collars as part of the body of the stabilizer will help keep the hole plumb as the weight of the drill string is then pulled by gravity to keep the hole in a plumb manner. Some other key tips in keeping your well in plumb is to prevent using pulldown on your drill if at all possible. Pull- down pushes the bit down the wellbore and this can and will most likely put your well out of plumb. We worked on one well that was 25 feet out of plumb at 750 feet! This well was drilled using pulldown and was subsequently abandoned by the owner who had a new well drilled. Staying in Line Let's focus on the cousin of plumbness: alignment. Alignment is, in short, the ability to keep the hole in line to allow the full clearance of a 40-foot dummy, ½-inch diameter less than the borehole size, to be lowered the full length of the borehole to the deepest depth the pump will be set, or in some cases, a liner. This specification was written to ensure a large diameter pump bowl section and column pipe could be set into the well without binding or becoming stuck in the borehole. STRAIGHT HOLE DRILLING Plumbness and alignment can affect the performance of a well system. DRAWING FROM THE WELL GARY SHAWVER, MGWC Plumbness and alignment may affect the ability of the drilling contractor to complete the well in a manner acceptable by today's standards. 46 March 2016 WWJ waterwelljournal.com

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