Water Well Journal
Issue link: http://read.dmtmag.com/i/465664
T here's been much discussion about the plumbness and alignment of water wells and how important alignment is for the installation of line shaft pumps. Some aspects of the discussion apply to wells destined to be equipped with submersible pumps. Discussions of well alignment have typically centered on concerns that if the well is too crooked or out of plumb, a pump will not operate properly once it has been installed. The problem, though, with having well alignment stan- dards tied to pump installation concerns is by the time it's time to set the pump, virtually nothing can be done to correct a misalignment problem. This article is about drilling straight boreholes in order to have straighter wells. Plumbness and alignment are combined here for purpose of this piece. There are two components to drilling a straight borehole. The first is setting up the drill rig and using proper drilling tools and techniques. The second is obtaining deviation read- ings of the borehole from plumb while drilling. Knowing if the borehole is drifting away from straight or plumb gives the contractor an opportunity to make corrections before complet- ing a well. Setting It Up Drilling a straight borehole begins with properly and se- curely setting up the drill rig. Some well drillers have set up their drill rig with almost no cribbing or jack supports with— not surprisingly—disastrous results. This is not only courting disaster for losing a rig if the ground shifts, but is hardly a stable platform for drilling a straight borehole. It takes only a small shifting of the earth beneath a jack to topple a rig, and smaller unseen shifts in the ground beneath the rig can cause the borehole to drift off of plumb. Setting up the drill rig with adequate ground support is the first step toward drilling a straight borehole. Frequently checking the plumbness of the drill rig by a bubble level on the table or a transit shot of the mast will tell you if the rig's footing has shifted and the drill string is no longer plumb. Heavy timbers, railroad ties, plates of heavy metal, and even "I" beams can be used to distribute the mass of the drill rig and drill string over a larger area, thus reducing the bear- ing of each jack support on a small point. Setting up a stable platform from which to drill will enhance your chances of drilling a straighter borehole. Having the Tools The next step is choosing the right tools for your job. If the task is to drill a 22-inch-diameter borehole with mud rotary using 4½-inch drill pipe, you probably better begin by drilling a smaller pilot borehole with appropriately sized drill collars or stabilizers, taking alignment readings every 100 feet, and re-drilling or reaming sections anytime the pilot borehole appears to be drifting off plumb. How do you know if it's drifting? There are alignment tools you can run inside your drill pipe telling you if you're not drilling a straight, plumb borehole. Verification of plumb- ness of the borehole can be obtained quickly and easily every hundred feet or so. These are not gyro-driven logging tools, but are driller- operated drift indicators much like the Totco tool shown in Figure 1. Typically described as deviation indicators, these tools can be purchased or rented and indicate borehole devia- tion from vertical. They are driller-operated drift indicators run on a wire line, telling contractors if the drill pipe at the bit is tilted or plumb in the borehole. Users set a timer indicating the delay setting necessary to get the deviation tool lowered down the drill pipe to the drill bit. It's a long, skinny wire line tool that flexes and bends with the drill pipe. When the timer goes off, it drops a plumb bob that strikes a target the driller has put into the device. The Totco target (Figure 2) has concentric circles on a small paper template and receives two punch marks when the plumb bob has been released. The driller sets the timer before sending the tool down the drill pipe on a wire line until it reaches the drill bit. At the scheduled time, the plumb bob drops and makes an indentation in the target as to the frac- tional number of degrees the borehole is out of plumb. The tool is removed and the dots on the target are immedi- ately read. The entire alignment test takes only a few minutes depending on how deep the borehole is at the time. STRAIGHT WELLS continues on page 22 It takes only a small shifting of the earth to topple a rig, and smaller unseen shifts in the ground beneath the rig can cause the borehole to drift off of plumb. Twitter @WaterWellJournl WWJ March 2015 21 ON TARGET Straight wells require straight drilling methods. By Gary L. Hix, RG, CWD/PI A contractor uses a tool to determine if the borehole he is working on is straight and plumb.